MicroRNA-196a targets annexin A1: a microRNA-mediated mechanism of annexin A1 downregulation in cancers.

Suppression of annexin A1 (ANXA1), a mediator of apoptosis and inhibitor of cell proliferation, is well documented in various cancers but the underlying mechanism remains unknown. We investigated whether decreased ANXA1 expression was mediated by microRNAs (miRNAs), which are small, non-coding RNAs that negatively regulate gene expression. Using Sanger miRBase, we identified miR-584, miR-196a and miR-196b as potential miRNAs targeting ANXA1. Only miRNA-196a showed significant inverse correlation with ANXA1 mRNA levels in 12 cancer cell lines of esophageal, breast and endometrial origin (Pearson's correlation -0.66, P=0.019), identifying this as the candidate miRNA targeting ANXA1. Inverse correlation was also observed in 10 esophageal adenocarcinomas (Pearson's correlation -0.64, P=0.047). Analysis of paired normal/tumor tissues from additional 10 patients revealed an increase in miR-196a in the cancers (P=0.003), accompanied by a decrease in ANXA1 mRNA (P=0.004). Increasing miR-196a levels in cells by miR-196a mimics resulted in decreased ANXA1 mRNA and protein. In addition, miR-196a mimics inhibited luciferase expression in luciferase plasmid reporter that included predicted miR-196a recognition sequence from ANXA1 3'-untranslated region confirming that miR-196a directly targets ANXA1. miR-196a promoted cell proliferation, anchorage-independent growth and suppressed apoptosis, suggesting its oncogenic potential. This study demonstrated a novel mechanism of post-transcriptional regulation of ANXA1 expression and identified miR-196a as a marker of esophageal cancer.

Expression of sigma 1 receptor in human breast cancer.

The sigma 1 receptor (S1R) represents a unique drug-binding site that is distinct from any other receptors. We examined S1R expression in human breast cancer and assessed the activity of S1R ligands in breast cancer cell lines. One-hundred nine breast specimens from normal breast, benign breast disease and cancer were examined with immunohistochemistry or RT-PCR and six different cell lines were also evaluated. S1R mRNA overexpression was detected in 64% of breast cancers compared to normal breast tissue. Immunohistochemistry showed positive epithelial cell staining in 60% of invasive and 41% of in situ cancers, 75% of ductal hyperplasia and in 33% of normal breast. The pattern of expression was more diffuse in invasive breast carcinoma compared to other conditions (p = 0.02). S1R expression was neither a prognostic nor a predictive factor for efficacy of adjuvant chemotherapy but the study only included 58 cancer patients and therefore the statistical power is limited. MDA-MB-361, MDA-MB-435, BT20 and MCF7 cells all expressed S1R protein by Western blot. The non-specific S1R ligands haloperidol, reduced haloperidol and progesterone produced a dose-dependent inhibition of the growth at high (>10 microM) concentrations. Reduced haloperidol also showed additive cytotoxic effects when combined with doxorubicin, vinorelbine , paclitaxel and docetaxel in vitro. The S1R-specific ligand, SKF 10047 demonstrated the least growth inhibitory activity and showed no interaction with chemotherapy. These results demonstrate that some normal and most neoplastic breast epithelial cells and cell lines commonly express S1R. High concentrations of haloperidol inhibit the growth of these cells and potentiate the effect of chemotherapy in vitro.

Differential expression of MUC2 and MUC5AC mucin genes in primary ovarian and metastatic colonic carcinoma.

Colonic adenocarcinoma, the most common tumor metastatic to the ovary, may closely mimic primary ovarian adenocarcinoma, especially that of mucinous or endometrioid histology. The differential diagnosis is important for therapeutic considerations. Mucin gene expression is relatively organ-specific and may therefore have use in distinguishing between colonic carcinomas metastatic to the ovary and primary ovarian tumors. In this study, we compared the expression of MUC2 and MUC5AC apomucins in 10 colonic adenocarcinomas metastatic with the ovary, 10 ovarian endometrioid carcinomas (4 primary, 6 metastatic), and 32 primary mucinous ovarian tumors (12 cystadenomas, 10 borderline tumors, and 10 cystadenocarcinomas). Monoclonal antibodies CCP58 and 45M1 were used for immunostains of MUC2 and MUC5AC apomucin, respectively. All but 1 of the 10 metastatic colon adenocarcinomas expressed MUC2, whereas none expressed MUC5AC. None of the 10 endometrioid carcinomas expressed MUC2, and only 2 showed weak immunoreactivity with MUC5AC. All 32 primary mucinous ovarian tumors expressed MUC5AC. The percentages of MUC2-positive immunostaining for cystadenomas, borderline tumors, and cystadenocarcinomas were 0% (0/12), 50% (5/10), and 70% (7/10) respectively. These studies show that MUC2 and MUC5AC are useful markers in the distinction between colonic carcinoma metastatic to the ovary and primary ovarian carcinoma.

The gonadotropin-releasing hormone receptor gene promoter directs pituitary-specific oncogene expression in transgenic mice.

Our previous work has shown that 1.2 kb of the 5' flanking region of the mouse GnRH receptor (mGnRH-R) gene is sufficient to direct tissue-specific expression in vitro. In this study, we have used the cell-specific regulatory sequences of the mGnRH-R gene promoter to target the expression of the simian virus 40 virus T antigen (TAg) to the pituitary gland of transgenic mice. A hybrid transgene, GnRH-R/TAg, was prepared using the -1164/+52 region of the mGnRH-R gene and +2533/+5234 sequences encoding the large T antigen of the simian virus 40. Two founders developed tumors of apparent pituitary origin at 44 (M28, female) and 50 (M25, male) days of age. M28 and M25 mice were about 50% underweight, and their gonads were grossly underdeveloped compared with wild-type litter mates. A third male founder, M29, developed a tumor at a later time (109 days). M29 was able to breed successfully and stably transmit the GnRH-R/TAg transgene. Mice of the M29 transgene line developed tumors at 4-5 months of age. Gross examination showed that the tumors extend from the sella and infiltrate into the inferior surface of the brain. In small tumors collected from young transgenic animals, normal pituitary cells as well as transition areas of increasing cellular atypia are evident. Frankly malignant cells are seen in all tumors. The pituitary tumors express the alpha-, FSHbeta-, and LHbeta-subunits and the GnRH-R messenger RNA, all markers of a gonadotrope but not of other anterior pituitary cell lineages. In summary, our studies indicate that 1.2 kb of the 5'-flanking region of the mGnRH-R gene can be used to target expression specifically to the gonadotropes of the pituitary gland in transgenic mice. The GnRH-R gene promoter-directed expression appears to be cell-specific and results in the formation of tumors that are primarily of gonadotropic origin.

The different forms of the prolactin receptor in the rat corpus luteum: developmental expression and hormonal regulation in pregnancy.

The corpora lutea of pregnancy in the rat are highly dependent on the action of PRL and PRL-like hormones to hypertrophy and to produce progesterone needed for the maintenance of gestation. Two forms of the PRL receptor (PRL-R), designated as long (PRL-RL) and short (PRL-RS), have been described in rat tissues. To determine whether both forms are present in the corpus luteum during pregnancy and to examine the developmental and hormonal regulation of their expression, total RNA isolated from corpora lutea at different stages of pregnancy and from highly luteinized granulosa cells subjected to different hormonal treatments were analyzed by semiquantitative RT-PCR. Immunoblotting of luteal proteins from early and late pregnancy was also performed to determine if the pattern of PRL-R proteins follows that of PRL-R messenger RNA (mRNA) expression. In addition, the correlation between the well characterized PRL-regulated gene, 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD), and PRL-R gene expression was investigated during the time of luteolysis. Both PRL-RL and PRL-RS mRNA and protein were expressed in corpora lutea of pregnancy, with the long form being the most dominant at all stages. Whereas no changes in mRNA level of either PRL-RL or PRL-RS were found until day 20 of gestation, a profound decline in PRL-R mRNA and protein for both receptor types occurred at the end of pregnancy. This drop in PRL-R expression was accompanied by a sharp and abrupt expression of 20alpha-HSD mRNA. Studies performed in vivo and in luteinized cells in culture indicate that PRL can up-regulate the expression of the PRL-RL mRNA, an effect prevented by the tyrosine kinase inhibitor, genistein. PRL-RL mRNA was also selectively increased by cAMP. In summary, the results of this investigation have established that: 1) the corpus luteum of pregnancy expresses both the short and long forms of the PRL-R with the long form being more abundant; 2) the mRNA for both forms of the PRL-R remains at constant levels throughout pregnancy but drops before parturition; 3) the decline in PRL-R mRNA at the end of pregnancy is accompanied by a dramatic rise in 20alpha-HSD; 4) PRL is able to increase the expression of PRL-R mRNA; and that 5) both A kinase and tyrosine kinase mediated pathways appear to participate in the up-regulatory mechanism involved in PRL-R mRNA expression.

PRAP, a prolactin receptor associated protein: its gene expression and regulation in the corpus luteum.

We have recently identified, characterized, and cloned a luteal microsomal 32-kDa phosphoprotein that we named PRAP (for PRL-receptor associated protein), and we have demonstrated that PRAP binds to the intracellular domain of the short but not the long form of the PRL receptor. In this study, we used PRAP cDNA to examine the tissue specificity, the developmental expression, and the hormonal regulation of PRAP gene expression. Northern blot analysis revealed that in the corpus luteum, PRAP cDNA hybridized to multiple transcripts (5.5 kb, 4.3 kb, and 1.8 kb), with the smallest transcript (1.8 kb) corresponding to the size of the cDNA clone. However, none of these transcripts were detected in any other tissues examined. PRAP appears to be tightly regulated by steroids and PRL. When pregnant rats were treated with aminoglutethimide, a steroid synthesis inhibitor, all three PRAP transcripts became barely detectable. Similar results were obtained when all luteotropic support was removed by hypophysectomy and hysterectomy. Estradiol up-regulated PRAP expression and, more specifically, the two lower transcripts. PRL had no stimulatory effect on PRAP messenger RNA (mRNA) expression but caused a substantial increase in the level of PRAP protein when administered to hypophysectomized pregnant rat, suggesting that PRL may stabilize this protein. Similar dissociation between levels of mRNA and protein were observed during luteal development. Although both PRAP mRNA and protein were barely detectable in early pregnancy, their expression increased abruptly from midpregnancy; however, whereas levels of PRAP mRNA declined from day 18, those of the protein remained elevated until parturition. In summary, results of this study have defined the tissue specificity and developmental expression of PRAP mRNA during pregnancy. The data have also revealed that the gene expression of this protein is up-regulated by estradiol, suggesting a pivotal role for PRAP in the synergistic action of estradiol and PRL on the function of the rat corpus luteum.

Transcriptional activation of the gonadotropin-releasing hormone receptor gene by activin A.

It has been reported that activin A stimulates the synthesis of the GnRH receptors (GnRHR) in rat pituitary cultures. However, the role of activin A in the regulation of the GnRHR gene at the molecular level is not known. In the present work, we have studied the regulation of the GnRHR gene by activin A in the gonadotrope cell line, alpha T3-1, where the GnRHR gene is highly expressed. First, we demonstrate that these cells express the mRNAs of three types of activin receptors: I, II, and IIB. Activin A increases GnRHR mRNA levels in a dose-and time-dependent manner, with maximal stimulation (2.5 +/- 0.5-fold) occurring with a dose of 20 ng/ml after 36 h of incubation. To ascertain whether this effect occurs at the transcriptional level, we performed nuclear run-off experiments in alpha T3-1 cells, which demonstrate a 1.6-fold increase in the levels of newly synthesized GnRHR mRNA in response to activin A. To investigate further the effect of activin A on the transcription of the GnRHR gene, alpha T3-1 cells were transiently transfected with a mouse GnRHR promoter/luciferase reporter gene (GnRHR-Luc) and challenged with activin A. Luciferase activity increases in response to activin A to the same extent (2.4 +/- 0.4-fold) and with similar dose-response and time-course profiles as the mRNA levels. Follistatin (100 ng/ml), a well known activin antagonist, completely abolishes the activin A effect on both mRNA levels and GnRHR-Luc activity. Follistatin also decreases the basal expression of the GnRHR gene by 33% as determined by GnRHR-Luc activity. This, together with our demonstration of the presence of the inhibin beta B-subunit mRNA in alpha T3-1 cells, suggests a potential paracrine/autocrine role of endogenous activin B on the regulation of the GnRHR gene in these cells. To provide evidence for biological significance of activin A stimulation of GnRHR gene expression, the response of a human gonadotropin alpha-subunit promoter/luciferase reporter gene (alpha Gon-Luc) to GnRH was assessed in alpha T3-1 cells pretreated with activin A. Activin enhances the stimulation of alpha Gon-Luc activity by GnRH by 1.6 +/- 0.4-fold. These data demonstrate that activin A can stimulate the expression of the GnRHR gene at the transcriptional level. Furthermore, transfection studies localize the activin responsive element to 1.2 kb of the 5'-flanking region of the GnRHR gene. Transcriptional activation of the GnRHR gene by activin A may serve as a mechanism for the modulation of gonadotrope responsiveness to GnRH.

Isolation and characterization of the 5'-flanking region of the mouse gonadotropin-releasing hormone receptor gene.

The GnRH receptor (GnRH-R) is a cell surface, G protein-coupled receptor that is highly expressed in pituitary gonadotropes. Activation of the receptor by GnRH stimulates the release of FSH and LH. Pituitary GnRH-R numbers and, hence, gonadotrope responsiveness to GnRH vary under different conditions and are regulated to a large extent by GnRH itself. To study the transcriptional regulation of the GnRH-R gene, a genomic clone containing 1.2 kilobases (kb) of the 5'-flanking region of mouse GnRH-R gene was isolated and characterized. A major transcriptional start site was identified 62 nucleotides upstream of the translational start site by primer extension and ribonuclease protection analyses. The promoter region does not contain canonical TATA sequences in the appropriate location. To determine whether this putative promoter is functional, it was subcloned into a luciferase reporter plasmid (GnRH-RLuc), and its transient expression was studied in cell lines of gonadotrope (alpha T3-1) and somatolactotrope (GH3) origins as well as those of nonpituitary origin (JEG-3 and CV-1). Luciferase activity was increased in alpha T3-1 (246-fold +/- 34.5-fold; P < 0.005) compared with the promoterless vector control but was considerably lower in GH3 (41-fold +/- 3.9-fold; P < 0.005), JEG-3 (12-fold +/- 0.9-fold; P < 0.005) and CV-1 (8-fold +/- 1.3-fold) indicating that GnRH-RLuc is preferentially expressed in cells of gonadotrope origin. Furthermore, GnRH agonist stimulated luciferase activity 3.4-fold +/- 0.3-fold (P < 0.005) above basal levels in GH3 cells cotransfected with rat GnRH-R complementary DNA, indicating that the GnRH-R promoter sequence is responsive to this ligand. In summary, we have identified and partially characterized the promoter region of the mouse GnRH-R and demonstrated that the regulatory elements for tissue-specific expression as well as for GnRH regulation are present within a 1.2-kb 5'-flanking region of the mouse GnRH-R gene.

Isolation and characterization of a rat luteal cDNA encoding 20 alpha-hydroxysteroid dehydrogenase.

We report the isolation and characterization of a full length cDNA encoding rat 20 alpha hydroxysteroid dehydrogenase derived from rat corpus luteum RNA. The predicted amino acid sequence of the protein encoded by the 20 alpha HSD clone is composed of 323 amino acids possessing an approximate molecular weight of 37 kDa. The sequence of peptides derived from the purified protein was found in the translated sequence of the open reading frame. cDNA and amino acid sequence indicate that the rat ovarian 20 alpha HSD belongs to the aldo-keto reductase family of enzymes. Northern analysis revealed a 1.2 Kb 20 alpha HSD mRNA in corpora lutea undergoing luteolysis. Prolactin reduced markedly 20 alpha HSD mRNA expression. No signal was detected in other tissues examined, demonstrating the specific expression of this enzyme in the corpus luteum.

Identification of a major prolactin-regulated protein as 20 alpha-hydroxysteroid dehydrogenase: coordinate regulation of its activity, protein content, and messenger ribonucleic acid expression.

We have previously reported that an abundant 37,000 mol wt protein with a pI of 6.15 (37K) is expressed specifically in the corpus luteum and is markedly inhibited by PRL. To identify the 37K, amino acid sequence analysis of the protein was performed. The 37K protein showed sequence similarity with rabbit 20 alpha-hydroxysteroid dehydrogenase (20 alpha HSD), chlordecone reductase, prostaglandin synthase, and 3 alpha-hydroxysteroid dehydrogenase, which are members of the aldo-keto reductase group of enzymes that catalyze the NADPH-dependent reduction of carbonyl compounds. Comparison of 20 alpha HSD activity with the level of 37K in the corpus luteum throughout pregnancy demonstrated a close correlation between enzyme activity and luteal levels of the protein. Both protein and enzyme activity were low early in pregnancy, reached a nadir between days 5-19, and reappeared abruptly between days 19-21 of pregnancy. To establish that the enzyme activity is intrinsic to the 37K, the protein was purified from sodium dodecyl sulfate-polyacrylamide electrophoresis gels (SDS-PAGE), renatured, and assayed for 20 alpha HSD activity. The renatured protein exhibited substantial 20 alpha HSD activity. As 20 alpha HSD is known to play a major role in the termination of pregnancy in the rat, it was of interest to examine whether the rapid appearance of the 37 K protein at the end of pregnancy is accompanied by the induction of 20 alpha HSD gene expression. Northern blot analysis using a rabbit cDNA for 20 alpha HSD indicated that the pattern of 20 alpha HSD mRNA expression in the corpus luteum closely paralleled the ontogeny of 20 alpha HSD enzyme activity as well as 37K protein levels. Our studies demonstrated that 20 alpha HSD protein and mRNA levels are coordinately regulated, and that the profound inhibitory effect of PRL on 20 alpha HSD activity is apparently due to inhibition of 20 alpha HSD gene expression, leading to the disappearance of the protein from the corpus luteum.

Prolactin regulation of the calmodulin-dependent protein kinase III elongation factor-2 system in the rat corpus luteum.

A M(r) 100,000 phosphoprotein in the corpus luteum was identified as elongation factor 2 (EF-2). Since prolactin (PRL) is necessary for optimal luteal development and protein synthesis, we determined whether this hormone affects the content and/or phosphorylation of EF-2 in the corpus luteum. PRL treatment enhanced the Ca2+/calmodulin (CaM)-dependent phosphorylation of endogenous EF-2 in luteal cytoplasmic extracts. Immunoblot analysis revealed that PRL had no effect on EF-2 levels, but examination of luteal EF-2 by two-dimensional isoelectric focusing/SDS-polyacrylamide gel electrophoresis showed that PRL increased the relative amount of the most basic dephosphorylated forms of EF-2. This suggests that PRL induces net dephosphorylation of the protein in vivo. Since EF-2 phosphorylation is regulated by both Ca2+/CaM-dependent kinase III (CaM kinase III) and protein phosphatase 2A, we examined the effect of PRL on both enzymes. Paradoxically, PRL enhanced the in vitro activity of CaM kinase III, possibly reflecting increased kinase levels, but had no effect on phosphatase activity. These results suggest that PRL maintains luteal EF-2 in a relatively dephosphorylated state in vivo by limiting the availability of Ca2+ and/or CaM to CaM kinase III. These data provide strong evidence for a role of the EF-2/CaM kinase III system in PRL action in the corpus luteum.

Hormonal and immunological characterization of the 32 kilodalton ovarian-specific protein.

Recent studies from this laboratory have shown that the large luteal cell of the pregnant rat contains an abundant 32 kilodalton (32K) phosphoprotein which is up-regulated by estradiol. In order to assess the potential importance of this protein and to more fully understand its function, a specific polyclonal antibody was produced against the 32K and was used to examine its intraovarian localization, its tissue specificity, and its developmental regulation. Immunocytochemical localization of the 32K in the ovary of the pregnant rat found this protein to be selectively and abundantly expressed in the corpus luteum. Immunofluorescence study of small and large luteal cell populations clearly revealed an extensive localization of the 32K in the large luteal cells. Western blot analysis revealed that the 32K was absent from all steroidogenic and nonsteroidogenic tissues. Whereas this protein was absent from all other tissues examined in the rat, it was clearly expressed in corpora lutea of different animal species, including the mouse, hamster, cow, human, and pig. Although undetectable by immunohistochemistry, Western blot analysis showed this protein to be present in the follicle but at levels markedly lower than in the corpus luteum. Analysis of theca and granulosa cells revealed the presence of the 32K in both cell types. To further examine the developmental expression of this protein throughout gestation, Western blot analysis of microsomal fractions isolated from rat corpora lutea on days 3-21 of pregnancy was performed. The 32K was detected at low levels in early pregnancy, increased markedly on day 11, reached a peak on days 14-15, and remained elevated through day 21. Treatment with estradiol and PRL increased the content of the 32K in the corpus luteum. Human CG, known to cause follicular development to the preovulatory stage and to enhance luteal estradiol synthesis, also increased levels of the 32K in the corpus luteum, while it concomitantly decreased this protein in the follicle. In summary, the presence of a unique ovarian-specific 32 kilodalton protein has been established. This protein, which is present in low abundance in theca and granulosa cells, is localized to the large luteal cell and becomes abundantly expressed during midpregnancy, a time when there is a remarkable increase in luteal cell size and activity. Results of this study also demonstrate a multihormonal regulation of the 32K by tropic hormones. Thus, because of its apparent uniqueness and its timely and highly regionalized expression, the 32K may play a central role in the regulation of corpus luteum growth and function.

Prolactin action on luteal protein expression in the corpus luteum.

Although it is well established that PRL is essential for luteal cell steroidogenesis and growth in the rat, its exact mechanism of action remains unknown. Whereas PRL stimulates growth and induces the content of specific proteins in several target tissues, its effect on proteins in the corpus luteum has not been examined. To determine whether PRL affects the synthesis of specific luteal protein(s), corpora lutea were obtained from rats hypophysectomized on day 3 of pregnancy and then treated with or without PRL (125 micrograms x 2/day) for 4 days. In this rat model, corpora lutea are exquisitely responsive to PRL and produce high levels of progesterone in response to PRL stimulation. Analysis of cytosolic proteins on one- and two-dimensional gel electrophoresis revealed a dramatic inhibitory effect of PRL on a 37,000 mol wt (MW) protein. This PRL-regulated protein (PRP) resolved into five separate isoelectric variants (pIs 5.5, 5.6, 6.15, 6.6, and 6.85). Since differences in phosphorylation state can alter the isoelectric point of proteins, we examined the possibility that the 37,000 MW PRP is a substrate for phosphorylation. Luteal homogenates were incubated with [32P]ATP in the presence or absence of Ca2+, Ca2+/calmodulin, Ca2+/phospholipid, or cAMP. Phosphorylation of PRP was not affected by PRL treatment or the addition of specific cofactors. The least abundant isoelectric species (pI 6.85) was identified by Western blot analysis as annexin I, a known regulator of phospholipase A2 and prostaglandin synthesis. To determine whether the other four isoelectric species represent variants of the same protein, we developed a polyclonal antibody to the 6.15 isoelectric species which is remarkably regulated by PRL. In the absence of PRL, the 6.15 isoelectric species (37K) is the major protein of the PRP band. Conversely, PRL treatment resulted in the virtual disappearance of this luteal protein. The antibody recognized the 37K alone, indicating that the other 37,000 MW isoelectric species were distinct proteins. To examine the time course of PRL action on the expression of the 37K, luteal cells from day 3 pregnant rats were cultured with different doses of PRL from 6 h to 5 days. Western blot analysis of luteal cellular proteins indicated that PRL caused a decrease in the expression of the 37K within 6 h of treatment. Although it is well known that estradiol together with PRL is required for optimal growth of the rat corpus luteum, estradiol alone had no inhibitory action on the 37K nor did it affect the inhibitory action of PRL.(ABSTRACT TRUNCATED AT 400 WORDS)