Analysis of a human placental lactogen gene promoter

Human placental lactogen (hPL) and human growth hormone (hGH) comprise a multigene family that share $>$90% nucleic acid sequence homology including 500 bp of 5$\sp\prime$ flanking sequence. Despite these similarities, hGH is produced in the anterior pituitary while hPL is expressed in the placenta. For most genes studied to date, regulation of expression occurs by alterations at the level of transcriptional initiation. Nuclear proteins bind specific DNA sequences in the promoter to regulate gene expression. In this study, the hPL$\sb3$ promoter was analyzed for DNA sequences that contribute to its expression. The interaction between the hPL$\sb3$ promoter and nuclear proteins was examined using nuclear extracts from placental and non-placental cells.^ To identify regulatory elements in the promoter of the hPL$\sb3$ gene, 5$\sp\prime$ deletion mutants were constructed by cleaving 1200 bp of upstream sequence with various restriction enzymes. These DNA fragments were ligated 5$\sp\prime$ to a promoterless bacterial gene chloramphenicol acetyltransferase (CAT) and transfected into JEG-3 cells, a human placental choriocarcinoma cell line. The level of CAT activity reflects the ability of the promoter mutants to activate transcription. Deletion of the sequence between $-$142 bp and $-$129 bp, relative to the start of transcription, resulted in an 8-fold decrease in CAT activity. Nuclear proteins from JEG-3, HeLa, and HepG2 (human liver cells), formed specific binding complexes with this region of the hPL$\sb3$ promoter, as shown by gel mobility shift assay. The $-$142 bp to $-$129 bp region contains a sequence similar to that of a variant binding site for the transcription factor Sp1. Sp1-like proteins were identified by DNA binding assay, in the nuclear extracts of the three cell lines. A series of G nucleotides in the hPL$\sb3$ promoter regulatory region were identified by methylation interference assay to interact with the DNA-binding proteins and the pattern obtained is similar to that for other Sp1 binding sites that have been studied. This suggests that hPL$\sb3$ may be transcriptionally regulated by Sp1 or a Sp1-like transacting factor. ^

EXPRESSION OF THE HUMAN PLACENTAL LACTOGEN GENES

The placenta is the site of synthesis of various peptide and steroid hormones related to pregnancy. Human placental lactogen (hPL) is the predominant peptide hormone secreted by term placenta and its synthesis is tissue-specific and coupled to placenta development. The objective of this work was to study the structure and expression of the hPL.^ Poly(A('+))RNA from human term placenta was translated in a mouse-derived cell-free system. A major band corresponding to pre-hPL and a minor band comigrating with mature hPL, represent (TURN)15% of the total radioactively labeled proteins. Analysis of the poly(A('+))RNA showed a prominent band at approximately 860 nucleotides. A corresponding band was observed in Northern blots of total RNA, hybridized with {('32)P}-labeled recombinant plasmid containing a portion of hPL cDNA. Similar analyses of nuclear RNA showed at least four additional bands at 990, 1200, 1460 and 1760 nucleotides, respectively, which are likely precursors of hPL mRNA. Poly(A('+))RNA was used to construct a cDNA library, of which approximately 5% of the clones were found to hybridize to hPL DNA sequences. Heteroduplexes constructed between a clone containing a 815 bp hPL cDNA insert and a hPL genomic DNA clone revealed four small intervening sequences which can account for the lengths observed in hnRNA molecules.^ Recombinant plasmid HCS-pBR322 containing a 550 bp insert of a cDNA transcript of human placental lactogen (hPL) mRNA was ('3)H-labeled an hybridized in situ to human chromosome preparations. These experiments allowed assignment of the hPL and growth hormone (hGH) genes, which have over 90% nucleotide homology in their coding sequences, to band q22-24 of chromosome 17. A gene copy number experiment showed that both genes are present in (TURN)3 copies per haploid genome.^ Experiments were designed to determine if all members of the hPL gene cluster, consisting of four non-allelic genes, are transcribed in term placenta. Advantage was taken of differences in restriction endonuclease sites in the coding portions of the different hPL genes, to distinguish the putative cDNAs of the transcriptionally active genes. Two genes were found to be represented in the cDNA library and their cDNA transcripts were isolated and characterized. Three independent methods showed that their corresponding mRNAs are about equally represented in the hPL mRNA population. The two cDNAs code for prehPL proteins which differ at a single amino acid position. However the secreted hPLs have identical amino acid sequences. A tetramer insertion duplication was found in a palindrome area of the 3' untranslated region of one of the hPL mRNAs. ^

Regulation of sex hormone dependent growth by a serum borne inhibitor

This thesis project focused on understanding the basic process controlling cell proliferation in sex-steroid hormone dependent cancers. The availability of inculture models using cloned cell lines offers the greatest advantage for studying the control of this event. Incubation of cloned sex-hormone sensitive cells in medium containing increasing concentrations of sex-hormone stripped serum, results in a dose dependent growth inhibition; this inhibition is reversed by the addition of physiological concentrations of steroid hormones. The mechanisms explaining this phenomenon are not yet fully understood, but different theories propose the existence in serum of a sex hormone binding protein with growth inhibitory properties. We were able to identify a protein that specifically binds sex hormones in rat and horse serum with affinities 10-fold lower to the ones observed with the classic sex-hormone binding globulin (SHBG) in humans. Purification of this protein on a large scale Lowed a more detailed analysis. The putative sex-hormone binding protein has an apparent molecular weight of 386 KDa. SDS-PAGE with commassie staining of the purified product, displayed a pattern non-characteristic of SMG, but all bands cross-reacted with a commercial anti-SMG antibody in western analysis. Titrations of the purified product on cell proliferation assays using sex-hormone dependent lines, resulted in a dose dependent growth inhibition. This inhibition was reversed by the addition of sex hormones. Our results indicate that we have identified and purified a sex-hormone binding protein in serum with characteristics similar to SHBG and with cell growth inhibitory properties. ^

Significance of Increased Tissue Transglutaminase in Hormone Refractory Prostate Cancer

The progression of hormone responsive to hormone refractory prostate cancer poses a major clinical challenge in the successful treatment of prostate cancer. The hormone refractory prostate cancer cells exhibit resistance not only to castrate levels of testosterone, but also to other therapeutic modalities and hence become lethal. Currently, there is no effective treatment available for managing this cancer. These observations underscore the urgency to investigate mechanism(s) that contribute to the progression of hormone-responsive to hormone-refractory prostate cancer and to target them for improved clinical outcomes. Tissue transglutaminase (TG2) is a multifunctional pro-inflammatory protein involved in diverse physiological processes such as inflammation, tissue repair, and wound healing. Its expression is also implicated in pathological conditions such as cancer and fibrosis. Interestingly, we found that the androgen-independent prostate cancer cell lines, which lacked androgen receptor (AR) expression, contained high basal levels of tissue transglutaminase. Inversely, the cell lines that expressed androgen receptor lacked transglutaminase expression. This attracted our attention to investigate the possible role this protein may play in the progression of prostate cancer, especially in view of recent observations that its expression is linked with increased invasion, metastasis, and drug resistance in multiple cancer cell types. The results we obtained were rather surprising and revealed that stable expression of tissue transglutaminase in androgen-sensitive LNCaP prostate cancer cells rendered these cells independent of androgen for growth and survival by silencing the AR expression. The AR silencing in TG2 expressing cells (TG2-infected LNCaP and PC-3 cells) was due to TG2-induced activation of the inflammatory nuclear transcription factor-kB (NF-kB). Thus, TG2 induced NF-kB was found to directly bind to the AR promoter. Importantly, TG2 protein was specifically recruited to the AR promoter in complex with the p65 subunit of NF-kB. Moreover, TG2 expressing LNCaP and PC-3 cells exhibited epithelial-to-mesenchymal transition, as evidenced by gain of mesenchymal (such as fibronectin, vimentin, etc.) and loss of epithelial markers (such as E-cadherin, b-catenin). Taken together, these results suggested a new function for TG2 and revealed a novel mechanism that is responsible for the progression of prostate cancer to the aggressive hormone-refractory phenotype.

A study of factors regulating the autonomous proliferation of the steroid hormone-induced LJ6195 murine reproductive tract tumor

Neonatal estrogen treatment of BALB/c mice results in the unregulated proliferation of the cervicovaginal epithelium and eventually tumorigenesis. The conversion of the normally estrogen responsive cyclic proliferation of the vaginal epithelium to a continuous estrogen-independent pattern of growth is a complex phenomenon. The aim of this study was to gain an understanding of the mechanism(s) by which steroid hormone administration during a critical period of development alters the cyclic proliferation of vaginal epithelium, ultimately leading to carcinogenesis in the adult animal.^ The LJ6195 murine cervicovaginal tumor was induced by treating newborn female BALB/c mice with 20 $\mu$g 17$\beta$-estradiol plus 100 $\mu$g progesterone for the first 5 days after birth. In contrast to proliferation of the normal vaginal epithelium, proliferation of LJ6195 is not regulated by estradiol. Northern blot analysis of RNA from vaginal tracts of normal mice, neonatal-estrogen treated mice, and LJ6195 indicate that there is an alteration in the expression of several genes such as the estrogen receptor, c-fos, and HER2/neu. In response to neonatal estrogen treatment, the estrogen receptor is down regulated in the murine vaginal tract. Therefore, the estrogen-independent nature of this tissue is established as early as 3 months after treatment. There is strong evidence that the proliferation of LJ6195 is regulated through an autocrine growth pathway. The LJ6195 tumor expresses mRNA for the epidermal growth factor receptor. In addition, conditioned medium from the LJ6195 tumor cell line contains a growth factor(s) with epidermal growth factor-like activity. Conditioned medium from the LJ6195 cell line stimulated the proliferation of the EGF-dependent COMMA D mouse mammary gland cell line in a dose-dependent manner. The addition of an anti-mEGF-antibody to LJ6195 cell cultures significantly decreased growth. These results suggest that the EGF-receptor mediated growth pathway may play a role in regulating the estrogen-independent proliferation of the LJ6195 tumor. ^

Nuclear functions of dynein light chain 1 in hormone action

It is widely accepted that the process of breast cancer tumorigenesis involves estrogen receptor-alpha (ER)-regulated stimulatory pathways, which feed into survival, cell cycle progression and proliferative response. Recent data from Kumar laboratory indicate that dynein light chain 1 (DLC1) plays a role in survival, motility and invasiveness, all of which are required for a successful tumorigenesis process. In the present research, we have discovered a mechanistic bidirectional regulatory link between the DLC1 and ER. We found that DLC1 facilitates ligand-induced ER transactivation involving the recruitment of the DLC1-ER complex to ER-target genes. To gain insights into the mechanism by which DLC1 regulates the ER pathway, we set out to identify novel DLC1-interacting proteins. Among other proteins, we identified KIBRA and Ciz1 as two novel DLC1-interacting proteins. We found that the KIBRA-DLC1 complex is recruited to ER-responsive promoters, and that KIBRA-DLC1 interaction is needed for the recruitment of ER to its targets as well as for ER's transactivation function. Finally, we found that KIBRA utilizes its histone H3interacting glutamic acid-rich region to regulate the transactivation activity of ER. During the course of this work, we also discovered that DLC1 interacts with Cdk2 and Ciz1, and such interactions play a direct accelerating role in the G1-S transition of breast cancer cells. While delineating the role of Ciz1 in hormone-responsive cancer cells, we found that Ciz1 is an estrogen-responsive gene, and acts as a co-regulator of ER. Accordingly, Ciz1 overexpression in breast cancer cells conferred estrogen hypersensitivity, promoted the growth-rate, anchorage-independency and tumorigenic properties. Collectively, findings made during the course of the present dissertation research introduced two new molecular players in the action of ER in breast cancer cells, with a particular focus on cell cycle progression and ER-chromatin target regulation. In addition, findings presented here provide novel mechanistic insight about the contribution of DLC1 and its interacting proteins in amplifying the hormone action and promoting the process of breast cancer tumorigenesis. ^