Progressive Purkinje Cell Degeneration in tambaleante Mutant Mice Is a Consequence of a Missense Mutation in HERC1 E3 Ubiquitin Ligase

The HERC gene family encodes proteins with two characteristic domains: HECT and RCC1-like. Proteins with HECT domain shave been described to function as ubiquitin ligases, and those that contain RCC1-like domains have been reported to function as GTPases regulators. These two activities are essential in a number of important cellular processes such as cell cycle, cell signaling, and membrane trafficking. Mutations affecting these domains have been found associated with retinitis pigmentosa, amyotrophic lateral sclerosis, and cancer. In humans, six HERC genes have been reported which encode two subgroups of HERC proteins: large (HERC1-2) and small (HERC3-6). The giant HERC1 protein was the first to be identified. It has been involved in membrane trafficking and cell proliferation/growth through its interactions with clathrin, M2-pyruvate kinase, and TSC2 proteins. Mutations affecting other members of the HERC family have been found to be associated with sterility and growth retardation. Here, we report the characterization of a recessive mutation named tambaleante, which causes progressive Purkinje cell degeneration leading to severe ataxia with reduced growth and lifespan in homozygous mice aged over two months. We mapped this mutation in mouse chromosome 9 and then performed positional cloning. We found a GuA transition at position 1448, causing a Gly to Glu substitution (Gly483Glu) in the highly conserved N- terminal RCC1-like domain of the HERC1 protein. Successful transgenic rescue, with either a mouse BAC containing the normal copy of Herc1 or with the human HERC1 cDNA, validated our findings. Histological and biochemical studies revealed extensive autophagy associated with an increase of the mutant protein level and a decrease of mTOR activity. Our observations concerning this first mutation in the Herc1 gene contribute to the functional annotation of the encoded E3 ubiquitin ligase and underline the crucial and unexpected role of this protein in Purkinje cell physiology.

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2-(4-IODO-2,5-DIMETOXIFENIL)-N-[(2-METOXIFENIL)METIL]ETAMINA OU 25I-NBOME: CARACTERIZAÇÃO QUÍMICA DE UMA DESIGNER DRUG

Drug trafficking and the introduction of new drugs onto the illicit market are one of the main challenges of the forensic community. In this study, the chemical profile of a new designer drug, 2-(4-iodine-2,5-dimethoxyphenyl)-n-[(2-methoxyphenyl)methyl]etamine or 25I-NBOMe was explored using thin layer chromatography (TLC), ultraviolet-visible spectrophotometry (UV-Vis), attenuated total reflection with Fourier transform infrared spectroscopy(ATR-FTIR), gas chromatography mass spectrometry (GC-MS) and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR MS). First, the TLC technique was effective for identifying spots related to 25C-, 25B- and 25I-NBOMe compounds, all with the same retention factor, Rf ≈ 0.50. No spot was detected for 2,5-dimethoxy-4-bromoamphetamine, 2,5-Dimethoxy-4-chloroamphetamine or lysergic acid diethylamide compounds. ATR-FTIR preserved the physical-chemical properties of the material, whereas GC-MS and ESI-MS showed better analytical selectivity. ESI(+)FT-ICR MS was used to identify the exact mass (m/z428.1706 for the [M + H]+ ion), molecular formula (M = C18H22INO3), degree of unsaturation (DBE = 8) and the chemical structure (from collision induced dissociation, CID, experiments) of the 25I-NBOMe compound. Furthermore, the ATR-FTIR and CID results suggested the presence of isomers, where a second structure is proposed as an isomer of the 25I-NBOMe molecule.

The Integrin Tail: A Tale of Cell Motility and Division

Integrin transmembrane receptor functions are regulated by adaptor molecules binding to their alpha and beta subunit intracellular domains, or tails, thus affecting integrin traffic and adhesion during e.g. cell motility. Interestingly, many cellular proteins function in both cell motility and cell division, thus raising the possibility that integrins might be involved in regulating the cell cycle. A thorough understanding of cell division is essential in cell biology and in human malignancies. It is well established that failures to complete cell cycle can give rise to genetically unstable cells with tumorigenic properties. Transformed cells promote the disruption of intercellular adhesions such as tight junctions, and this correlates with the onset of cell motility, invasion and unfavorable prognosis in cancer. In this study, we analyzed integrin regulation, mediated by adaptor binding to the  subunit tail, during cell motility and cell division. We revealed a novel molecular mechanism by which Rab21, through association with the integrin alpha subunits, drives integrin endosomal traffic during mitotic phases. In addition, we found indications for this finding in vivo, as RAB21 gene deletions were mapped in ovarian and prostate cancer samples. Importantly, the multinucleated phenotype of cultured ovarian cancer cells could be reverted by Rab21 overexpression. In this thesis work, we also show how the tight junction protein ZO-1 unexpectedly interacts with the 5 integrin cytoplasmic domain in the lamellipodia to promote cell motility and at the cleavage furrow to support separation of the daughter cells. The alpha5-ZO-1 complex formation was dependent on PKC which regulates ZO-1 phosphorylation and its subcellular localization. In addition, by an in situ detection method, we showed that a subset of metastatic human lung cancers expressed the alpha5beta-ZO-1 complex. Taken together, we were able to identify new molecular pathways that regulate integrin functions in an alpha tail-mediated fashion. These findings firmly suggest that genetic alterations in integrin traffic may lead to progression of tumorigenesis as a result of failed cell division. Also, the interplay of integrins and ZO-1 in forming spatially regulated adhesive structures broadens our view of crosstalk between pathways and distinct adhesive structures that can be involved in cancer cell biology.

Novel Players in the Integrin Signaling Orchestra: TCPTP and MDGI

Metastases are the major cause of cancer deaths. Tumor cell dissemination from the primary tumor utilizes dysregulated cellular adhesion and upregulated proteolytic degradation of the extracellular matrix for progeny formation in distant organs. Integrins are transmembrane adhesive receptors mediating cellcell and cellmatrix interactions that are crucial for regulating cell migration, invasion, proliferation, and survival. Consequently, increased integrin activity is associated with augmented migration and invasion capacity in several cancer types. Heterodimeric integrins consist of an alpha - and beta-subunit that are held together in a bent conformation when the receptor is inactive, but extension and separation of subdomains is observed during receptor activation. Either inside-out or outside-in activation of receptors is possible through the intracellular molecule binding to an integrin cytoplasmic domain or extracellular ligand association with an integrin ectodomain, respectively. Several regulatory binding partners have been characterized for integrin cytoplasmic beta-domains, but the regulators interacting with the cytoplasmic alpha-domains have remained elusive. In this study, we performed yeast two-hybrid screens to identify novel binding partners for the cytoplasmic integrin alpha-domains. Further examination of two plausible candidates revealed a significant coregulatory role of an integrin alpha-subunit for cellular signaling processes. T-cell protein tyrosine phosphatase (TCPTP) showed a specific interaction with the cytoplasmic tail of integrin alpha1. This association stimulated TCPTP phosphatase activity, leading to negative regulation of epidermal growth factor receptor (EGFR) signaling and diminished anchorage-independent growth. Another candidate, mammary-derived growth inhibitor (MDGI), exhibited binding to several different integrin cytoplasmic alpha-tails through a conserved GFFKR sequence. MDGI overexpression in breast cancer cells altered EGFR trafficking and caused a remarkable accumulation of EGFR in the cytoplasm. We further demonstrated in vivo that MDGI expression induced a novel form of anti-EGFR therapy resistance. Moreover, MDGI binding to α-tails retained integrin in an inactive conformation attenuating integrin-mediated adhesion, migration, and invasion. In agreement with these results, sustained MDGI expression in breast cancer patients correlated with an increased 10-year distant disease-free survival. Taken together, the integrin signaling network is far from a complete view and future work will doubtless broaden our understanding further.

The Influence of Diet and Microbes on Colonic Immune Regulation and their Implications on Type 1 Diabetes

Dietary and microbial factors are thought to contribute to the rapidly increasing prevalence of T1D in many countries worldwide. The impact of these factors on immune regulation and diabetes development in non-obese diabetic (NOD) mice are investigated in this thesis. Diabetes can be prevented in NOD mice through dietary manipulation. Diet affects the composition of intestinal microbiota, which may subsequently influence intestinal immune homeostasis. However, the specific effects of anti-diabetogenic diets on gut immunity and the explicit associations between intestinal immune disruption and type 1 diabetes onset remain unclear. The research presented herein demonstrates that newly weaned NOD mice suffer from a mild level of colitis, which shifts the colonic immune cell balance towards a proinflammatory status. Several aberrations can also be observed in the peritoneal B cells of NOD mice; an increase in activation marker expression, increased trafficking to the pancreatic lymph nodes and significantly higher antigen presenting cell (APC) efficiency towards insulin-specific T cells. A shift towards inflammation is likewise observed in the colon of germ-free NOD mice, but signs of peritoneal B cell activation are lacking in these mice. Remarkably, most of the abnormalities in the colon, peritoneal macrophages and the peritoneal B cell APC activity of NOD mice are abrogated when NOD mice are maintained on a diabetes-preventive, soy-based diet (ProSobee) from the time of weaning. Dietary and microbial factors hence have a significant impact on colonic immune regulation and peritoneal B cell activation and it is suggested that these factors influence diabetes development in NOD mice.

Ultrastructural calli analysis of Inga vera Willd. subsp. Affinis (DC.) T.D. Penn

Subcellular changes are relevant to understand plant organogenesis and embryogenesis in the early stages of cell development. The cytology during cell development in tissue culture is however still poorly characterized. This study aimed to characterize the ultrastructural differences related to callogenesis of anthers, ovaries, leaf and nodal segments of Inga vera Willd. subsp. Affinis (DC.) T.D. Penn. Flower buds, nodal segments and leaves were disinfected and inoculated in test tubes containing MS medium with 3% sucrose and 4.5µM 2.4-D, except for leaf callogenesis, where 9µM of this auxin was used, and for the callogenesis of anthers and ovaries, where the culture medium was enriched with 0.25% activated charcoal and 90µM PVP. After 45 days in culture medium, the anther, ovary, leaf and nodal segment calli were fixed in Karnovisky and prepared for visualization by scanning and transmission electron microscopy. Ultrastructural differences were observed among the callus cells of anthers, ovaries, segments and leaves. There was no evidence of somatic embryo formation in the anther, leaf and nodal segment calli, in spite of some embryogenic characteristics in the cells. The ovary calli, with indications of embryo formation, seem to be the most responsive explant source for embryogenesis.

The Dual Role of HIF Hydroxylase PHD3 in Cancer Cell Survival

Most advanced tumours face periods of reduced oxygen availability i.e. hypoxia. During these periods tumour cells undergo adaptive changes enabling their survival under adverse conditions. In cancer hypoxia-induced cellular changes cause tumour progression, hinder cancer treatment and are indicative of poor prognosis. Within cells the main regulator of hypoxic responses is the hypoxia-inducible factor (HIF). HIF governs the expression of over a hundred hypoxia-inducible genes that regulate a number of cellular functions such as angiogenesis, glucose metabolism and cell migration. Therefore the activity of HIF must be tightly governed. HIF is regulated by a family of prolyl hydroxylase enzymes, PHDs, which mark HIF for destruction in normoxia. Under hypoxic conditions PHDs lose much of their enzymatic activity as they need molecular oxygen as a cofactor. Out of the three PHDs (PHD1, 2 and 3) PHD2 has been considered to be the main HIF-1 regulator in normoxic conditions. PHD3 on the other hand shows the most robust induction in response to oxygen deprivation and it has been implied as the main HIF-1 regulator under prolonged hypoxia. SQSTM1/p62 (p62) is an adaptor protein that functions through its binding motifs to bring together proteins in order to regulate signal transduction. In non-stressed situations p62 levels are kept low but its expression has been reported to be upregulated in many cancers. It has a definitive role as an autophagy receptor and as such it serves a key function in cancer cell survival decisions. In my thesis work I evaluated the significance of PHD3 in cancer cell and tumour biology. My results revealed that PHD3 has a dual role in cancer cell fate. First, I demonstrated that PHD3 forms subcellular protein aggregates in oxygenated carcinoma cells and that this aggregation promotes apoptosis induction in a subset of cancer cells. In these aggregates an adaptor protein SQSTM1/p62 interacts with PHD3 and in so doing regulates PHD3 expression. SQSTM1/p62 expression is needed to keep PHD3 levels low in normoxic conditions. Its levels rapidly decrease in response to hypoxia allowing PHD3 protein levels to be upregulated and the protein to be diffusely expressed throughout the cell. The interaction between PHD3 and SQSTM1/p62 limits the ability of PHD3 to function on its hydroxylation target protein HIF-1alpha. Second, the results indicate that when PHD3 is upregulated under hypoxia it protects cancer cells by allowing cell cycle to proceed from G1 to S-phase. My data demonstrates that PHD3 may either cause cell death or protect the cells depending on its expression pattern and the oxygen availability of tumours.

JNK, a versatile regulator of kinesin-1 transport and cytoskeleton dynamics

C-Jun N-terminal kinase (JNK) is traditionally recognized as a crucial factor in stress response and inducer of apoptosis upon various stimulations. Three isoforms build the JNK subfamily of MAPK; generally expressed JNK1 and JNK2 and brain specific JNK3. Degenerative potency placed JNK in the spotlight as potential pharmacological option for intervention. Unfortunately, adverse effects of potential drugs and observation that expression of only JNK2 and JNK3 are induced upon stress, restrained initial enthusiasm. Notably, JNK1 demonstrated atypical high constitutive activity in neurons that is not responsive to cellular stresses and indicated existence of physiological activity. This thesis aimed at revealing the physiological functions of JNK1 in actin homeostasis through novel effector MARCKS-Like 1 (MARCKSL1) protein, neuronal trafficking mediated by major kinesin-1 motor protein and microtubule (MT) dynamics via STMN2/SCG10. The screen for novel physiological JNK substrates revealed specific phosphorylation of C-terminal end of MARCKSL1 at S120, T148 and T183 both ex vivo and in vitro. By utilizing site-specific mutagenesis, various actin dynamics and migrations assays we were able to demonstrate that JNK1 phosphorylation specifically facilitates F-actin bundling and thus filament stabilisation. Consecutively, this molecular mechanism was proved to enhance formation of filopodia; cell surface projections that allow cell sensing surrounding environment and migrate efficiently. Our results visualize JNK dependent and MARCKSL1 executed induction of filopodia in neurons and fibroblast indicating general mechanism. Subsequently, inactivation of JNK action on MARCKSL1 shifts cellular actin machinery into lamellipodial dynamic arrangement. Tuning of actin cytoskeleton inevitably melds with cell migration. We observed that both active JNK and JNK pseudo-phosphorylated form of MARCKSL1 reduce actin turnover in intact cells leading to overall diminished cell motility. We demonstrate that tumour transformed cells from breast, prostate, lung and muscle-derived cancers upregulate MARCKSL1. We showed on the example of prostate cancer PC-3 cell line that JNK phosphorylation negatively controls MARCKSL1 ability to induce migration, which precedes cancer cell metastasis. The second round of identification of JNK physiological substrates resulted in detection of predominant motor protein kinesin-1 (Kif5). Mass spectrometry detailed analysis showed evident endogenous phosphorylation of kinesin-1 on S176 within motor domain that interacts with MT. In vitro phosphorylation of bacterially expressed kinesin heavy chain by JNK isoforms displayed higher specificity of JNK1 when compared to JNK3. Since, JNK1 is constitutively active in neurons it signified physiological aspect of kinesin-1 regulation. Subsequent biochemical examination revealed that kinesin-1, when not phosphorylated on JNK site, exhibits much higher affinity toward MTs. Expression of the JNK non-phosphorable kinesin-1 mutant in intact cells as well as in vitro single molecule imaging using total internal reflection fluorescence microscopy indicated that the mutant loses normal speed and is not able to move processively into proper cellular compartments. We identify novel kinesin-1 cargo protein STMN2/SCG10, which along with known kinesin-1 cargo BDNF is showing impaired trafficking when JNK activity is inhibited. Our data postulates that constitutive JNK activity in neurons is crucial for unperturbed physiologically relevant transport of kinesin-1 dependant cargo. Additionally, my work helps to validate another novel physiological JNK1 effector STMN2/SCG10 as determinant of axodendritic neurites dynamics in the developing brain through regulation of MT turnover. We show successively that this increased MT dynamics is crucial during developmental radial migration when brain layering occurs. Successively, we are able to show that introduction of JNK phosphorylation mimicking STMN2/SCG10 S62/73D mutant rescues completely JNK1 genetic deletion migration phenotype. We prove that STMN2/SCG10 is predominant JNK effector responsible for MT depolymerising activity and neurite length during brain development. Summarizing, this work describes identification of three novel JNK substrates MARCKSL1, kinesin-1 and STMN2/SCG10 and investigation of their roles in cytoskeleton dynamics and cargo transport. This data is of high importance to understand physiological meaning of JNK activity, which might have an adverse effect during pharmaceutical intervention aiming at blocking pathological JNK action.

Integrins on the move

Cancer is a leading cause of death worldwide accounting for 13% of all deaths in 2005. The spread of cancer and formation of metastases is the major cause of mortality among cancer patients. The spread of cancer is based on the cancer cell’s ability to break away from the surrounding tissue and to migrate into new areas in the body. The ability of cells to bind its surroundings and to move is controlled by the mechanical cell surface adhesion receptors called the integrins. Integrins have a critical role in cell adhesion, cell motility and tissue homeostasis. By communicating with ECM, integrins transmit signals from the surrounding environment inside the cell and modulate the function of many important signalling pathways involved in cell survival, development, gene expression, proliferation, motility and cytoskeletal organization. During cell migration integrin-matrix adhesions are formed in front of the cell while rear-adhesions are released during migration. Integrins are endocytosed from the plasma-membrane into the cytoplasm and partly recycled back to new adhesion sites in a process called integrin trafficking. Also, the cell cytoskeleton and protrusions are important in cell migration. Finger-like actin protrusions called filopodia display an interesting cancer relevant cooperation with integrins that is required for cell migration. The expression and function of integrins changes markedly as cells acquire carcinogenic properties. Changed integrin function is partly responsible for detachment of tumor cells from neighbouring cells and for providing enhanced invasive capabilities for tumor cells to disseminate. Similarly, the formation of filopodia is increased in cancer. High myosin-10 expression is related to poor outcome in breast cancer and increased cell migration. The proper function of myosin-10 induced filopodia needs association with β1 integrins. The importance of integrin trafficking and filopodia formation is becoming increasingly more recognized in cancer. This thesis focusses on the role of integrins, integrin trafficking and myosin-10 induced filopodia cancer cell migration.

Fluorescence-based imaging of cellular defect in lysinuric protein intolerance (LPI)

Fluoresenssiperusteiset kuvantamismenetelmät lysinurisen proteiini-intoleranssin (LPI) soluhäiriön tutkimuksessa Lysinurinen proteiini-intoleranssi on suomalaiseen tautiperintöön kuuluva autosomaalisesti peit¬tyvästi periytyvä sairaus, jonka aiheuttaa kationisten aminohappojen kuljetushäiriö munuaisten ja ohutsuolen epiteelisolujen basolateraalikalvolla. Aminohappojen kuljetushäiriö johtaa moniin oirei¬siin, kuten kasvuhäiriöön, osteoporoosiin, immuunijärjestelmän häiriöihin, oksenteluun ja runsaspro¬teiinisen ravinnon nauttimisen jälkeiseen hyperammonemiaan. LPI-geeni SLC7A7 (solute carrier family 7 member 7) koodaa y+LAT1 proteiinia, joka on basolateraali¬nen kationisten ja neutraalien aminohappojen kuljettimen kevyt ketju, joka muodostaa heterodimee¬rin raskaan alayksikön 4F2hc:n kanssa. Tällä hetkellä SLC7A7-geenistä tunnetaan yli 50 LPI:n aiheut¬tavaa mutaatiota. Tässä tutkimuksessa erityyppisiä y+LAT1:n LPI-mutaatiota sekä yhdeksän C-terminaalista polypep¬tidiä lyhentävää deleetiota kuvannettiin nisäkässoluissa y+LAT1:n GFP (green fluorescent protein) -fuusioproteiineina. Tulokset vahvistivat muissa soluissa tehdyt havainnot siitä, että 4F2hc on edel¬lytyksenä y+LAT1:n solukalvokuljetukselle, G54V-pistemutantti sijaitsee solukalvolla samoin kuin vil¬lityyppinen proteiini, mutta lukukehystä muuttavia ja proteiinia lyhentäviä mutantteja ei kuljeteta solukalvoon. Lisäksi havaittiin, että poikkeuksena tästä säännöstä ovat y+LAT1-deleetioproteiinit, joista puuttui korkeintaan 50 C-terminaalista aminohappoa. Nämä lyhentyneet kuljettimet sijaitsevat solukalvolla kuten villityyppiset ja LPI-pistemutanttiproteiinit. Dimerisaation osuutta kuljetushäiriön synnyssä tutkittiin käyttämällä fluorescence resonance energy transfer (FRET) menetelmää. Heterodimeerin alayksiköistä kloonattiin ECFP (cyan) ja EYFP (yellow) fuusioproteiinit, joita ilmennettiin nisäkässoluissa, ja FRET mitattiin virtaussytometri-FRET -menetel¬mällä (FACS-FRET). Tutkimuksissa kaikkien mutanttien havaittiin dimerisoituvan yhtä tehokkaasti. Kul¬jetushäiriön syynä ei siten ole alayksiköiden dimerisaation estyminen mutaation seurauksena. Tutkimuksessa havaittiin, että kaikki mutantti-y+LAT1-transfektiot tuottavat vähemmän transfektoi¬tuneita soluja kuin villityyppisen y+LAT1:n transfektiot. Solupopulaatioissa, joihin oli tranfektoitu lu¬kukehystä muuttava tai stop-kodonin tuottava mutaatio havaittiin suurempi kuolleisuus kuin saman näytteen transfektoitumattomissa soluissa, kun taas villityyppistä tai G54V-pistemutanttia tuottavas¬sa solupopulaatiossa oli pienempi kuolleisuus kuin saman näytteen fuusioproteiinia ilmentämättö¬missä soluissa. Tulos osoittaa mutanttiproteiinien erilaiset vaikutukset niitä ilmentäviin soluihin, joko suoraan y+LAT1:n tai 4F2hc:n kautta aiheutuneina. LPIFin SLC7A7 lähetti-RNA:n määrä ei merkittävästi poikennut villityyppisen määrästä fibroblasteissa ja lymfoblasteissa. SLC7A7:n promoottorianalyysissä oli osoitettavissa säätelyalueita geenin 5’ ei-koo¬daavalla alueella sekä ensimmäisten kahden intronin alueella. LPI-taudin tautimekanismin kannalta keskeisin tekijä on kuitenkin aminohappokuljetuksen häiriö, jonka vaikutuksesta näistä aminohapoista riippuvaiset prosessit elimistössä eivät toimi normaalisti. Havaittu virheellinen y+LAT1/4F2hc kuljetuskompleksin sijainti edellyttää lisätutkimuksia sen mahdol¬lisen kliinisen merkityksen selvittämiseksi.

Regulation of cell fate by c-FLIP phosphorylation

Programmed cell death is an important physiological cellular process that maintains homeostasis and protects multicellular organisms from diseases. Apoptosis is the principal mode of cell death, which eliminates unwanted cells and an enormous effort has been made to understand the molecular mechanisms of the signaling pathway and its regulatory systems. Irregular apoptosis often has life-threatening consequences to humans, including cancer, autoimmune diseases and degenerative diseases. In cancer for example, cell death is an attractive target to eradicate uncontrollably proliferating cells that have disregard pro-apoptotic signaling. Targeted therapeutic approaches are not as effective as once expected, since now we know that the cell death pathways are not sole entities in cells, but are highly associated with various cellular processes. Proteins that regulate apoptosis can also control non-apoptotic signaling pathways. For example, c-FLIP is a protein that can either inhibit or promote caspase-8 activation, which is required to induce apoptosis. Not only has c-FLIP opposing effects on initiating apoptosis, but it also regulates various pro-survival signaling pathways in the cell. It is well known that protein expression level is a determinant of how c-FLIP can regulate different signaling pathways, but other regulatory mechanisms potentially affecting the role of c-FLIP are less well understood. This work addresses novel insights into the mechanisms of c-FLIP post-translational modifications and their functional consequences. We have identified that phosphorylation is an important inception for subcellular localization of c-FLIP, thereby dictating which apoptotic and non-apoptotic signaling pathways c-FLIP could regulate to promote cell survival. Furthermore, we have constructed mathematical models to unite independent studies to establish more systematic c-FLIP signaling pathways to understand the dynamics of extrinsically-induced apoptosis.

Virulence properties of Aggregatibacter actinomycetemcomitans biofilm and characterisation of its putative cytokine exploitation

Biofilms are surface-attached multispecies microbial communities that are embedded by their self-produced extracellular polymeric substances. This lifestyle enhances the survival of the bacteria and plays a major role in many chronic bacterial infections. For instance, periodontitis is initiated by multispecies biofilms. The phases of active periodontal tissue destruction and notably increased levels of proinflammatory mediators, such as the key inflammatory mediator interleukin (IL)-1beta, are typical of the disease. The opportunistic periodontal pathogen Aggregatibacter actinomycetemcomitans is usually abundant at sites of aggressive periodontitis. Despite potent host immune system responses to subgingival invaders, A. actinomycetemcomitans is able to resist clearance attempts. Moreover, some strains of A. actinomycetemcomitans can generate genetic diversity through natural transformation, which may improve the species’ adjustment tothe subgingival environment in the long term. Some biofilm forming species are known to bind and sense human cytokines. As a response to cytokines, bacteria may increase biofilm formation and alter their expression of virulence genes. Specific outer membrane receptors for interferon-γ or IL-1β have been characterised in two Gram-negative pathogens. Because little is known about periodontal pathogens’ ability to sense cytokines, we used A. actinomycetemcomitans as a model organism to investigate how the species responds to IL-1beta. The main aims of this thesis were to explore cytokine binding on single-species A. actinomycetemcomitans biofilms and to determine the effects of cytokines on the biofilm formation and metabolic activity of the species. Additionally, the cytokine’s putative internalisation and interaction with A. actinomycetemcomitans proteins were studied. The possible impact of biofilm IL-1beta sequestering on the proliferation and apoptosis of gingival keratinocyte cells was evaluated in an organotypic mucosa co-culture model. Finally, the role of the extramembranous domain of the outer membrane protein HofQ (emHofQ) in DNA binding linked to DNA uptake in A. actinomycetemcomitans was examined. Our main finding revealed that viable A. actinomycetemcomitans biofilms can bind and take up the IL-1β produced by gingival cells. At the sites of pathogen-host interaction, the proliferation and apoptosis of gingival keratinocytes decreased slightly. Notably, the exposure of biofilms to IL-1beta caused their metabolic activity to drop, which may be linked to the observed interaction of IL-1beta with the conserved intracellular proteins DNA binding protein HU and the trimeric form of ATP synthase subunit beta. A Pasteurellaceaespecific lipoprotein, which had no previously determined function, was characterized as an IL-1beta interacting membrane protein that was expressed in the biofilm cultures of all tested A. actinomycetemcomitans strains. The use of a subcellular localisation tool combined with experimental analyses suggested that the identified lipoprotein, bacterial interleukin receptor I (BilRI), may be associated with the outer membrane with a portion of the protein oriented towards the external milieu. The results of the emHofQ study indicated that emHofQ has both the structural and functional capability to bind DNA. This result implies that emHofQ plays a role in DNA assimilation. The results from the current study also demonstrate that the Gram-negative oral species appears to sense the central proinflammatory mediator IL-1beta.

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