Nuclear Factor-κB (NF-κB) Regulates Proliferation and Branching in Mouse Mammary Epithelium

The nuclear factor-κB (NF-κB) family of transcription factors has been shown to regulate proliferation in several cell types. Although recent studies have demonstrated aberrant expression or activity of NF-κB in human breast cancer cell lines and tumors, little is known regarding the precise role of NF-κB in normal proliferation and development of the mammary epithelium. We investigated the function of NF-κB during murine early postnatal mammary gland development by observing the consequences of increased NF-κB activity in mouse mammary epithelium lacking the gene encoding IκBα, a major inhibitor of NF-κB. Mammary tissue containing epithelium from inhibitor κBα (IκBα)-deficient female donors was transplanted into the gland-free mammary stroma of wild-type mice, resulting in an increase in lateral ductal branching and pervasive intraductal hyperplasia. A two- to threefold increase in epithelial cell number was observed in IκBα-deficient epithelium compared with controls. Epithelial cell proliferation was strikingly increased in IκBα-deficient epithelium, and no alteration in apoptosis was detected. The extracellular matrix adjacent to IκBα-deficient epithelium was reduced. Consistent with in vivo data, a fourfold increase in epithelial branching was also observed in purified IκBα-deficient primary epithelial cells in three-dimensional culture. These data demonstrate that NF-κB positively regulates mammary epithelial proliferation, branching, and functions in maintenance of normal epithelial architecture during early postnatal development.

Phenserine regulates translation of β-amyloid precursor protein mRNA by a putative interleukin-1 responsive element, a target for drug development

The reduction in levels of the potentially toxic amyloid-β peptide (Aβ) has emerged as one of the most important therapeutic goals in Alzheimer's disease. Key targets for this goal are factors that affect the expression and processing of the Aβ precursor protein (βAPP). Earlier reports from our laboratory have shown that a novel cholinesterase inhibitor, phenserine, reduces βAPP levels in vivo. Herein, we studied the mechanism of phenserine's actions to define the regulatory elements in βAPP processing. Phenserine treatment resulted in decreased secretion of soluble βAPP and Aβ into the conditioned media of human neuroblastoma cells without cellular toxicity. The regulation of βAPP protein expression by phenserine was posttranscriptional as it suppressed βAPP protein expression without altering βAPP mRNA levels. However, phenserine's action was neither mediated through classical receptor signaling pathways, involving extracellular signal-regulated kinase or phosphatidylinositol 3-kinase activation, nor was it associated with the anticholinesterase activity of the drug. Furthermore, phenserine reduced expression of a chloramphenicol acetyltransferase reporter fused to the 5′-mRNA leader sequence of βAPP without altering expression of a control chloramphenicol acetyltransferase reporter. These studies suggest that phenserine reduces Aβ levels by regulating βAPP translation via the recently described iron regulatory element in the 5′-untranslated region of βAPP mRNA, which has been shown previously to be up-regulated in the presence of interleukin-1. This study identifies an approach for the regulation of βAPP expression that can result in a substantial reduction in the level of Aβ.

Phytochrome Regulates Gibberellin Biosynthesis during Germination of Photoblastic Lettuce Seeds1

Germination of lettuce (Lactuca sativa L.) seed is regulated by phytochrome. The requirement for red light is circumvented by the application of gibberellin (GA). We have previously shown that the endogenous content of GA1, the main bioactive GA in lettuce seeds, increases after red-light treatment. To clarify which step of GA1 synthesis is regulated by phytochrome, cDNAs encoding GA 20-oxidases (Ls20ox1 and Ls20ox2, for L. sativa GA 20-oxidase) and 3β-hydroxylases (Ls3h1 and Ls3h2 for L. sativa GA 3β-hydroxylase) were isolated from lettuce seeds by reverse-transcription polymerase chain reaction. Functional analysis of recombinant proteins expressed in Escherichia coli confirmed that the Ls20ox and Ls3h encode GA 20-oxidases and 3β-hydroxylases, respectively. Northern-blot analysis showed that Ls3h1 expression was dramatically induced by red-light treatment within 2 h, and that this effect was canceled by a subsequent far-red-light treatment. Ls3h2 mRNA was not detected in seeds that had been allowed to imbibe under any light conditions. Expression of the two Ls20ox genes was induced by initial imbibition alone in the dark. The level of Ls20ox2 mRNA decreased after the red-light treatment, whereas that of Ls20ox1 was unaffected by light. These results suggest that red light promotes GA1 synthesis in lettuce seeds by inducing Ls3h1 expression via phytochrome action.

A Novel Gene, pmgA, Specifically Regulates Photosystem Stoichiometry in the Cyanobacterium Synechocystis Species PCC 6803 in Response to High Light1

Previously, we identified a novel gene, pmgA, as an essential factor to support photomixotrophic growth of Synechocystis species PCC 6803 and reported that a strain in which pmgA was deleted grew better than the wild type under photoautotrophic conditions. To gain insight into the role of pmgA, we investigated the mutant phenotype of pmgA in detail. When low-light-grown (20 μE m−2 s−1) cells were transferred to high light (HL [200μE m−2 s−1]), pmgA mutants failed to respond in the manner typically associated with Synechocystis. Specifically, mutants lost their ability to suppress accumulation of chlorophyll and photosystem I and, consequently, could not modulate photosystem stoichiometry. These phenotypes seem to result in enhanced rates of photosynthesis and growth during short-term exposure to HL. Moreover, mixed-culture experiments clearly demonstrated that loss of pmgA function was selected against during longer-term exposure to HL, suggesting that pmgA is involved in acquisition of resistance to HL stress. Finally, early induction of pmgA expression detected by reverse transcriptase-PCR upon the shift to HL led us to conclude that pmgA is the first gene identified, to our knowledge, as a specific regulatory factor for HL acclimation.

Ras Regulates the Polarity of the Yeast Actin Cytoskeleton through the Stress Response Pathway

Polarized growth in yeast requires cooperation between the polarized actin cytoskeleton and delivery of post-Golgi secretory vesicles. We have previously reported that loss of the major tropomyosin isoform, Tpm1p, results in cells sensitive to perturbations in cell polarity. To identify components that bridge these processes, we sought mutations with both a conditional defect in secretion and a partial defect in polarity. Thus, we set up a genetic screen for mutations that conferred a conditional growth defect, showed synthetic lethality with tpm1Δ, and simultaneously became denser at the restrictive temperature, a hallmark of secretion-defective cells. Of the 10 complementation groups recovered, the group with the largest number of independent isolates was functionally null alleles of RAS2. Consistent with this, ras2Δ and tpm1Δ are synthetically lethal at 35°C. We show that ras2Δ confers temperature-sensitive growth and temperature-dependent depolarization of the actin cytoskeleton. Furthermore, we show that at elevated temperatures ras2Δ cells are partially defective in endocytosis and show a delocalization of two key polarity markers, Myo2p and Cdc42p. However, the conditional enhanced density phenotype of ras2Δ cells is not a defect in secretion. All the phenotypes of ras2Δ cells can be fully suppressed by expression of yeast RAS1 or RAS2 genes, human Ha-ras, or the double disruption of the stress response genes msn2Δmsn4Δ. Although the best characterized pathway of Ras function in yeast involves activation of the cAMP-dependent protein kinase A pathway, activation of the protein kinase A pathway does not fully suppress the actin polarity defects, suggesting that there is an additional pathway from Ras2p to Msn2/4p. Thus, Ras2p regulates cytoskeletal polarity in yeast under conditions of mild temperature stress through the stress response pathway.

Role for the class A macrophage scavenger receptor in the phagocytosis of apoptotic thymocytes in vitro.

Numerous immature thymocytes undergo apoptosis and are rapidly engulfed by phagocytic thymic macrophages. The macrophage surface receptors involved in apoptotic thymocyte recognition are unknown. We have examined the role of the class A macrophage scavenger receptor (SR-A) in the engulfment of apoptotic thymocytes. Uptake of steroid-treated apoptotic thymocytes by thymic and inflammatory-elicited SR-A positive macrophages is partially inhibited by an anti-SR-A mAb and more completely by a range of scavenger receptor ligands. Thymic macrophages from mice with targeted disruption of the SR-A gene show a 50% reduction in phagocytosis of apoptotic thymocytes in vitro. These data suggest that SR-A may play a role in the clearance of dying cells in the thymus.

An estrogen receptor pathway regulates the telogen-anagen hair follicle transition and influences epidermal cell proliferation.

The hair follicle is a cyclic, self renewing epidermal structure which is thought to be controlled by signals from the dermal papilla, a specialized cluster of mesenchymal cells within the dermis. Topical treatments with 17-beta-estradiol to the clipped dorsal skin of mice arrested hair follicles in telogen and produced a profound and prolonged inhibition of hair growth while treatment with the biologically inactive stereoisomer, 17-alpha-estradiol, did not inhibit hair growth. Topical treatments with ICI 182,780, a pure estrogen receptor antagonist, caused the hair follicles to exit telogen and enter anagen, thereby initiating hair growth. Immunohistochemical staining for the estrogen receptor in skin revealed intense and specific staining of the nuclei of the cells of the dermal papilla. The expression of the estrogen receptor in the dermal papilla was hair cycle-dependent with the highest levels of expression associated with the telogen follicle. 17-beta-Estradiol-treated epidermis demonstrated a similar number of 5-bromo-2'-deoxyuridine (BrdUrd) S-phase cells as the control epidermis above telogen follicles; however, the number of BrdUrd S-phase basal cells in the control epidermis varied according to the phase of the cycle of the underlying hair follicles and ranged from 2.6% above telogen follicles to 7.0% above early anagen follicles. These findings indicate an estrogen receptor pathway within the dermal papilla regulates the telogen-anagen follicle transition and suggest that diffusible factors associated with the anagen follicle influence cell proliferation in the epidermis.

A developmental switch in lymphocyte homing receptor and endothelial vascular addressin expression regulates lymphocyte homing and permits CD4+ CD3- cells to colonize lymph nodes.

IN adult mice, the dominant adhesion molecules involved in homing to lymph nodes are L-selectin homing receptors on lymphocytes and the peripheral lymph node addressins on specialized high endothelial venules. Here we show that, from fetal life through the first 24 hr of life, the dominant adhesion molecules are the mucosal addressin MAdCAM-1 on lymph node high endothelial venules and its counterreceptor, the Peyer's patch homing receptor, integrin alpha 4 beta 7 on circulating cells. Before birth, 40-70% of peripheral blood leukocytes are L-selectin-positive, while only 1-2% expresses alpha 4 beta 7. However, the fetal lymph nodes preferentially attract alpha 4 beta 7-expressing cells, and this can be blocked by fetal administration of anti-MAdCAM-1 antibodies. During fetal and early neonatal life, when only MAdCAM-1 is expressed on high endothelial venules, an unusual subset of CD4 + CD3- cells, exclusively expressing alpha 4 beta 7 as homing receptors, enters the lymph nodes. Beginning 24 hr after birth a developmental switch occurs, and the peripheral node addressins are upregulated on high endothelial venules in peripheral and mesenteric lymph nodes. This switch in addressin expression facilitates tissue-selective lymphocyte migration and mediates a sequential entry of different cell populations into the lymph nodes.

Cross talk between cell death and cell cycle progression: BCL-2 regulates NFAT-mediated activation.

BCL-2-deficient T cells demonstrate accelerated cell cycle progression and increased apoptosis following activation. Increasing the levels of BCL-2 retarded the G0-->S transition, sustained the levels of cyclin-dependent kinase inhibitor p27Kip1, and repressed postactivation death. Proximal signal transduction events and immediate early gene transcription were unaffected. However, the transcription and synthesis of interleukin 2 and other delayed early cytokines were markedly attenuated by BCL-2. In contrast, a cysteine protease inhibitor that also blocks apoptosis had no substantial affect upon cytokine production. InterleUkin 2 expression requires several transcription factors of which nuclear translocation of NFAT (nuclear factor of activated T cells) and NFAT-mediated transactivation were impaired by BCL-2. Thus, select genetic aberrations in the apoptotic pathway reveal a cell autonomous coregulation of activation.

Nitric oxide regulates vascular cell adhesion molecule 1 gene expression and redox-sensitive transcriptional events in human vascular endothelial cells.

Decreased nitric oxide (NO) activity, the formation of reactive oxygen species, and increased endothelial expression of the redox-sensitive vascular cell adhesion molecule 1 (VCAM-1) gene in the vessel wall are early and characteristic features of atherosclerosis. To explore whether these phenomena are functionally interrelated, we tested the hypothesis that redox-sensitive VCAM-1 gene expression is regulated by a NO-sensitive mechanism. In early passaged human umbilical vein endothelial cells and human dermal microvascular endothelial cells, the NO donor diethylamine-NO (DETA-NO, 100 microM) reduced VCAM-1 gene expression induced by the cytokine tumor necrosis factor alpha (TNF-alpha, 100 units/ml) at the cell surface level by 65% and intracellular adhesion molecule 1 (ICAM-1) gene expression by 35%. E-selectin gene expression was not affected. No effect on expression of cell adhesion molecules was observed with DETA alone. Moreover, DETA-NO suppressed TNF-alpha-induced mRNA accumulation of VCAM-1 and TNF-alpha-mediated transcriptional activation of the human VCAM-1 promoter. Conversely, treatment with NG-monomethyl-L-arginine (L-NMMA, 1 mM), an inhibitor of NO synthesis, augmented cytokine induction of VCAM-1 and ICAM-1 mRNA accumulation. By gel mobility shift analysis, DETA-NO inhibited TNF-alpha activation of DNA binding protein activity to the VCAM-1 NF-kappa B like binding sites. Peroxy-fatty acids such as 13-hydroperoxydodecanoeic acid (linoleyl hydroperoxide) may serve as an intracellular signal for NF-kappa B activation. Using thin layer chromatography, DETA-NO (100 microM) suppressed formation of this metabolite, suggesting that DETA-NO modifies the reactivity of oxygen intermediates in the vascular endothelium. Through this mechanism, NO may function as an immunomodulator of the vessel wall and thus mediate inflammatory events involved in the pathogenesis of atherosclerosis.

I-TRAF is a novel TRAF-interacting protein that regulates TRAF-mediated signal transduction.

Tumor necrosis factor (TNF) receptor-associated factor (TRAF) proteins associate with and transduce signals from TNF receptor 2, CD40, and presumably other members of the TNF receptor superfamily. TRAF2 is required for CD40- and TNF-mediated activation of the transcription factor NF-kappa B. Here we describe the isolation and characterization of a novel TRAF-interacting protein, I-TRAF, that binds to the conserved TRAF-C domain of the three known TRAFs. Overexpression of I-TRAF inhibits TRAF2-mediated NF-kappa B activation signaled by CD40 and both TNF receptors. Thus, I-TRAF appears as a natural regulator of TRAF function that may act by maintaining TRAFs in a latent state.

The Mos/mitogen-activated protein kinase (MAPK) pathway regulates the size and degradation of the first polar body in maturing mouse oocytes.

Mos is an upstream activator of mitogen-activated protein kinase (MAPK) and, in mouse oocytes, is responsible for metaphase II arrest. This activity has been likened to its function in Xenopus oocytes as a component of cytostatic factor. Thus, Mos-deficient female mice (MOS-/-) are less fertile and oocytes derived from these animals fail to arrest at metaphase II and undergo parthenogenetic activation [Colledge, W. H., Carlton, M. B. L., Udy, C. B. & Evans, M. J. (1994) Nature (London) 370, 65-68 and Hashimoto, N., Watanabe, N., Furuta. Y., Tamemoto, B., Sagata, N., Yokoyama, M., Okazaki, K., Nagayoshi, M., Takeda, N., Ikawa, Y. & Aizawa, S. (1994) Nature (London) 370, 68-71]. Here we show that maturing MOS-/- oocytes fail to activate MAPK throughout meiosis, while p34cdc2 kinase activity is normal until late in metaphase II when it decreases prematurely. Phenotypically, the first meiotic division of MOS-/- oocytes frequently resembles mitotic cleavage or produces an abnormally large polar body. In these oocytes, the spindle shape is altered and the spindle fails to translocate to the cortex, leading to the establishment of an altered cleavage plane. Moreover, the first polar body persists instead of degrading and sometimes undergoes an additional cleavage, thereby providing conditions for parthenogenesis. These studies identify meiotic spindle formation and programmed degradation of the first polar body as new and important roles for the Mos/MAPK pathway.

Alternative splicing of agrin regulates its binding to heparin alpha-dystroglycan, and the cell surface.

Agrin is a basal lamina molecule that directs key events in postsynaptic differentiation, most notably the aggregation of acetylcholine receptors (AChRs) on the muscle cell surface. Agrin's AChR clustering activity is regulated by alternative mRNA splicing. Agrin splice forms having inserts at two sites (y and z) in the C-terminal region are highly active, but isoforms lacking these inserts are weakly active. The biochemical consequences of this alternative splicing are unknown. Here, the binding of four recombinant agrin isoforms to heparin, to alpha-dystroglycan (a component of an agrin receptor), and to myoblasts was tested. The presence of a four-amino acid insert at the y site is necessary and sufficient to confer heparin binding ability to agrin. Moreover, the binding of agrin to alpha-dystroglycan is inhibited by heparin when this insert is present. Agrin binding to the cell surface showed analogous properties: heparin inhibits the binding of only those agrin isoforms containing this four-amino acid insert. The results show that alternative splicing of agrin regulates its binding to heparin and suggest that agrin's interaction with alpha-dystroglycan may be modulated by cell surface glycosaminoglycans in an isoform-dependent manner.

A JAK-STAT pathway regulates wing vein formation in Drosophila.

We present evidence that the JAK-STAT signal transduction pathway regulates multiple developmental processes in Drosophila. We screened for second-site mutations that suppress the phenotype of the hyperactive hopTum-1 Jak kinase, and recovered a mutation that meiotically maps to the known chromosomal position of D-Stat, a Drosophila stat gene. This hypomorphic mutation, termed statHJ contains a nucleotide substitution in the first D-Stat intron, resulting in a reduction in the number of correctly processed transcripts. Further, the abnormally processed mRNA encodes a truncated protein that has a dominant negative effect on transcriptional activation by the wild-type cDNA in cell culture. statHJ mutants exhibit patterning defects that include the formation of ectopic wing veins, similar to those seen in mutants of the epidermal growth factor/receptor pathway. Abnormalities in embryonic and adult segmentation and in tracheal development were also observed. The hopTum-1 and statHJ mutations can partially compensate for each other genetically, and Hop overexpression can increase D-Stat transcriptional activity in vitro, indicating that the gene products interact in a common regulatory pathway.