Prolactin receptor gene diversity: structure and regulation

Effect of prolactin on cytotoxicity and oxidative stress in ovine ovarian granulosa cells

Background

Prolactin (PRL) has been reported to be associated with oxidative stress, which is an important contributor leading to cell apoptosis. However, little is known about the mechanisms underlying the effects of PRL on cytotoxicity and oxidative stress in ovine ovarian granulosa cells (GCs).

Methods

Ovine ovarian GCs were treated with 0, 4, 20, 100 and 500 ng/mL of PRL. Then, the cytotoxicity, cell viability, malondialdehyde (MDA), reactive oxygen species (ROS), superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) of GCs were detected. Additionally, 500 ng/mL PRL was chosen as the high PRL concentration (HPC) due to its high cytotoxicity and oxidative stress. Proteomic and metabonomic were performed to examine the overall difference in proteins and metabolic pathways between C (control: 0 ng/mL PRL) and P groups (500 ng/mL PRL).

Results

The results indicated that GCs treated with 4 ng/mL PRL significantly decreased (P < 0.05) the cytotoxicity, ROS and MDA, increased (P < 0.05) the cell viability, SOD and T-AOC, and the GCs treated with 500 ng/mL PRL showed the opposite trend (P < 0.05). Supplementation with 500 ng/mL PRL significantly increased the proteins of MT-ND1, MAPK12, UBA52 and BCL2L1, which were enriched in ROS and mitophagy pathways. Pathway enrichment analysis showed that the pentose phosphate pathway was significantly enriched in the P group.

Conclusion

A low concentration of PRL inhibited cytotoxicity and oxidative stress. HPC induced oxidative stress in ovine ovarian GCs via the pentose phosphate pathway by modulating the associated proteins MT-ND1 in ROS pathway and UBA52, MAPK12 and BCL2L1 in mitophagy pathway, resulting in cytotoxicity.

Prolactin receptor gene transcriptional control, regulatory modalities relevant to breast cancer resistance and invasiveness

The prolactin receptor (PRLR) is a member of the lactogen/cytokine receptor family, which mediates multiple actions of prolactin (PRL). PRL is a major hormone in the proliferation/differentiation of breast epithelium that is essential for lactation. It is also involved in breast cancer development, tumor growth and chemoresistance. Human PRLR expression is controlled at the transcriptional level by multiple promoters. Each promoter directs transcription/expression of a specific non-coding exon 1, a common non-coding exon 2 and coding exons E3-11. The identification of exon 11 of PRLR led to finding of alternative spliced products and two novel short forms (SF) that can inhibit the long form (LF) of PRLR activity with relevance in physiological regulation and breast cancer. Homo and heterodimers of LF and SF are formed in the absence of PRL that acts as a conformational modifier. Heterodimerization of SF with LF is a major mechanism through which SF inhibits some signaling pathways originating at the LF. Biochemical/molecular modeling approaches demonstrated that the human PRLR conformation stabilized by extracellular intramolecular S-S bonds and several amino acids in the extracellular D1 domain of PRLR SF are required for its inhibitory actions on PRLR LF-mediated functions. Studies in breast cancer cells demonstrated that the transcription of PRLR was directed by the preferentially utilized PIII promoter, which lacks an estrogen responsive element. Complex formation of non-DNA bound ERα dimer with Sp1 and C/EBPβ dimers bound to their sites at the PRLR promoter is required for basal activity. Estradiol induces transcriptional activation/expression of the PRLR gene, and subsequent studies revealed the essential role of autocrine PRL released by breast cancer cells and CDK7 in estradiol-induced PRLR promoter activation and upregulation. Other studies revealed stimulation of the PRLR promoter activity and PRLR LF protein by PRL in the absence of estrogen via the STAT5/phospho-ERα activation loop. Additionally, EGF/ERBB1 can induce the transcription of PRLR independent of estrogen and prolactin. The various regulatory modalities contributing to the upregulation of PRLR provide options for the development of therapeutic approaches to mitigate its participation in breast cancer progression and resistance.

Prolactin Regulates Pain Responses via a Female-Selective Nociceptor-Specific Mechanism

Many clinical and preclinical studies report an increased prevalence and severity of chronic pain among females. Here, we identify a sex-hormone-controlled target and mechanism that regulates dimorphic pain responses. Prolactin (PRL), which is involved in many physiologic functions, induces female-specific hyperalgesia. A PRL receptor (Prlr) antagonist in the hind paw or spinal cord substantially reduced hyperalgesia in inflammatory models. This effect was mimicked by sensory neuronal ablation of Prlr. Although Prlr mRNA is expressed equally in female and male peptidergic nociceptors and central terminals, Prlr protein was found only in females and PRL-induced excitability was detected only in female DRG neurons. PRL-induced excitability was reproduced in male Prlr⁺ neurons after prolonged treatment with estradiol but was prevented with addition of a translation inhibitor. We propose a novel mechanism for female-selective regulation of pain responses, which is mediated by Prlr signaling in sensory neurons via sex-dependent control of Prlr mRNA translation.

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Local or spinal PRL injection induces hyperalgesia in a female-selective manner

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Sensory neuron Prlr regulates tissue injury-induced pain only in females

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PRL regulates excitability in Prlr⁺ neurons depending on sex and estrogen

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Regulation of Prlr translation defines female-selective neuronal excitability

Prolactin receptor expression in mouse dorsal root ganglia neuronal subtypes is sex-dependent

Sensory neurones exhibit sex-dependent responsiveness to prolactin (PRL). This could contribute to sexual dimorphism in pathological pain conditions. The present study aimed to determine the mechanisms underlying sex-dependent PRL sensitivity in sensory neurones. A quantitative reverse transcriptase-polymerase chain reaction shows that prolactin receptor (Prlr) long and short isoform mRNAs are expressed at comparable levels in female and male mouse dorsal root ganglia (DRG). In Prlr^cre/+ ;Rosa26^{LSL-tDTomato/+} reporter mice, percentages of Prlr⁺ sensory neurones in female and male DRG are also similar. Characterisation of Prlr⁺ DRG neurones using immunohistochemistry and electrophysiology revealed that Prlr⁺ DRG neurones are mainly peptidergic nociceptors in females and males. However, sensory neurone type-dependent expression of Prlr is sex dimorphic. Thus, Prlr⁺ populations fell into three small- and two medium-large-sized sensory neuronal groups. Prlr⁺ DRG neurones are predominantly medium-large sized in males and are proportionally more comprised of small-sized sensory neurones in females. Specifically, Prlr⁺ /IB4⁺ /CGRP⁺ neurones are four- to five-fold higher in numbers in female DRG. By contrast, Prlr⁺ /IB4^- /CGRP⁺ /5HT3a⁺ /NPYR2^- are predominant in male DRG. Prlr⁺ /IB4^- /CGRP^- , Prlr⁺ /IB4^- /CGRP⁺ and Prlr⁺ /IB4^- /CGRP⁺ /NPYR2⁺ neurones are evenly encountered in female and male DRG. These differences were confirmed using an independently generated single-cell sequencing dataset. Overall, we propose a novel mechanism by which sensory neurone type-dependent expression of Prlr could explain the unique sex dimorphism in responsiveness of nociceptors to PRL.

Molecular characterization and an 80-bp indel polymorphism within the prolactin receptor (PRLR) gene and its associations with chicken growth and carcass traits

The prolactin receptor (PRLR), a type I cytokine receptor, must bind prolactin (PRL) to act on target cells to mediate various physiological functions, including reproduction and lactation. This study identified an 80-bp insertion/deletion (indel) polymorphism in the 3'-untranslated region (3'-UTR) of the chicken PRLR gene in 3736 individuals from 15 breeds and analyzed its associations with growth and carcass traits in an F₂ resource population. The results of the association analysis indicated that the 80-bp indel polymorphism was significantly (P < 0.05) or very significantly (P < 0.01) associated with multiple growth and carcass traits, such as body weight, leg weight, and shank length. In addition, we found that during the breeding process of commercial laying hens and commercial broilers, the 80-bp indel locus was artificially selected for the II genotype. Together, our findings reveal that this 80-bp indel polymorphism has potential as a new molecular marker for marker-assisted selection of chicken growth and carcass traits.

Activating the Prolactin Receptor: Effect of the Ligand on the Conformation of the Extracellular Domain

The prolactin receptor resides on the surface of the cell as a preformed dimer. This suggests that cell signaling is triggered by conformational changes within the extracellular domain of the receptors. Here, by using atomistic molecular dynamics simulations, we show that the removal of the ligand placental lactogen from the dimeric form of the prolactin receptor results in a relative reorientation of the two extracellular domains by 20-30°, which corresponds to a clockwise rotation of the domains with respect to each other. Such a mechanism of activation for the prolactin receptor is similar to that proposed previously in the case of the growth hormone receptor. In addition to the effect of the removal of the ligand, the mechanical coupling between the extracellular and transmembrane domains within a model membrane was also examined.

Molecular characterization of prolactin receptor (cPRLR) gene in chickens: gene structure, tissue expression, promoter analysis, and its interaction with chicken prolactin (cPRL) and prolactin-like protein (cPRL-L)

In this study, gene structure, tissue expression, and promoter usage of prolactin receptor (PRLR) and its interaction with prolactin (PRL) and the newly identified prolactin-like protein (PRL-L) were investigated in chickens. The results showed that (1) PRLR gene was found to consist of at least 25 exons by 5'-RACE and RT-PCR assays; (2) multiple PRLR 5'-UTR sequences different in exon composition were isolated from chicken liver or intestine by 5'-RACE and could be subdivided into type I and type II transcripts according to the first exon used (exon 1G or exon 1A); (3) PRLR Type I transcripts with exon 1G were detected to be predominantly expressed in adult kidney and small intestine by RT-PCR, implying their expression is likely controlled by a tissue-specific promoter (P1). By contrast, PRLR type II transcripts containing exon 1A are widely expressed in adult and embryonic tissues examined and their expression is controlled by a generic promoter (P2) near exon 1A, which was demonstrated to display promoter activities in cultured DF-1, HEK293 and LoVo cells by the dual-luciferase reporter assay; (4) Using a 5×STAT5-luciferase reporter system, cPRLR expressed in HepG2 cells was shown to be activated by recombinant cPRL and cPRL-L via interaction with PRLR membrane-proximal ligand-binding domain, suggesting that like cPRL, cPRL-L is also a functional ligand of cPRLR. Collectively, characterization of cPRLR gene helps to elucidate the roles of PRLR and its ligands in birds and provides insights into the regulatory mechanisms of PRLR expression conserved in birds and mammals.

Complex formation and interactions between transcription factors essential for human prolactin receptor gene transcription

The protein association of estrogen receptor α ERα with DNA-bound SP1 and C/EBPβ is essential for the 17β-estradiol (E2)-induced activation of human prolactin receptor (hPRLR) gene transcription. Protein-protein interaction and complex formation at the hPIII promoter of hPRLR was investigated. The basic region and leucine zipper (bZIP) of C/EBPβ, zinc finger (ZF) motifs of SP1, and the DNA binding domain of ERα were identified as regions responsible for the interactions between transfactors. The E2-induced interaction was confirmed by bioluminescence resonance energy transfer (BRET) assays of live cells. The combination of BRET/bimolecular luminescence complementation assay revealed that ERα exists as a constitutive homodimer, and E2 induced a change(s) in ERα homodimer conformation favorable for its association with C/EBPβ and SP1. Chromatin immunoprecipitation and small interfering RNA knockdown of members of the complex in breast cancer cells demonstrated the endogenous recruitment of components of the complex onto the hPIII promoter of the hPRLR gene. SP1 is the preferred transfactor for the recruitment of ERα to the complex that facilitates the C/EBPβ association. The E2/ERα-induced hPRLR transcription was demonstrated in ERα-negative breast cancer cells. This study indicates that the enhanced complex formation of ERα dimer with SP1 and C/EBPβ by E2 has an essential role in the transcriptional activation of the hPRLR gene.

Lactogens and estrogens in breast cancer chemoresistance

Tumor resistance to chemotherapy in advanced breast cancer is a major impediment to treatment success. Resistance can be induced by the drugs themselves or result from the action of internal factors. The role of hormones in chemoresistance has received little attention. This article focuses on two classes of hormones: lactogens and estrogens. Lactogens include prolactin, growth hormone and placental lactogen, all of which can activate the prolactin receptor. Estrogens include endogenous steroids and nonsteroidal compounds from the environment termed endocrine disruptors, all of which can activate 'classical' estrogen receptors (ERα and ERβ), as well as other types of receptors. Both lactogens and estrogens antagonize cytotoxicity of multiple chemotherapeutic agents through complementary mechanisms. The implications of chemoresistance by these hormones to patients with breast cancer, and the potential benefits of developing combinatorial anti-lactogen/anti-estrogen treatment regimens, are discussed.

Progesterone induces expression of the prolactin receptor gene through cooperative action of Sp1 and C/EBP

Prolactin (Prl) and progesterone (P) cooperate synergistically during mammary gland development and tumorigenesis. We hypothesized that one mechanism for these effects may be through mutual induction of receptors (R). EpH4 mouse mammary epithelial cells stably transfected with PR-A express elevated levels of PrlR mRNA and protein compared to control EpH4 cells that lack the PR. Likewise, T47D human breast cancer cells treated with P overexpress the PrlR and activate PrlR promoter III. PrlR promoter III does not contain a classical P response element but contains several binding sites for transcription proteins, including C/EBP, Sp1 and AP1, which may also interact with the PR. Using promoter deletion and site directed mutagenesis analyses as well as gel shift assays, cooperative activation of the C/EBP and adjacent Sp1A, but not the Sp1B or AP1, sites by P is shown to confer P responsiveness leading to increased PrlR transcription.

A novel estradiol/estrogen receptor alpha-dependent transcriptional mechanism controls expression of the human prolactin receptor

Prolactin exerts diverse functions in target tissues through its membrane receptors, and is a potent mitogen in normal and neoplastic breast cells. Estradiol (E(2)) induces human prolactin receptor (hPRLR) gene expression through stimulation of its generic promoter (PIII). This study identifies a novel E(2)-regulated non-estrogen responsive element-dependent transcriptional mechanism that mediates E(2)-induced hPRLR expression. E(2) stimulated transcriptional activity in MCF7A(2) cells transfected with PIII lacking an estrogen responsive element, and increased hPRLR mRNA and protein. The abolition of the E(2) effect by mutation of Sp1 or C/EBP elements that bind Sp1/Sp3 and C/EBPbeta within PIII indicated the cooperation of these transfactors in E(2)-induced transcription of the hPRLR. DNA affinity protein assay showed that E(2) induced estrogen receptor alpha (ERalpha) binding to Sp1/Sp3 and C/EBPbeta DNA-protein complexes. The ligand-binding domain of ERalpha was essential for its physical interaction with C/EBPbeta, and E(2) promoted this association, and its DNA binding domain was required for transactivation of PIII. Co-immunoprecipitation studies revealed tethering of C/EBPbeta to Sp1 by E(2)-activated ERalpha. Chromatin immunoprecipitation analysis showed that E(2) induced recruitment of C/EBPbeta, ERalpha, SRC1, p300, pCAF, TFIIB, and Pol II, with no change in Sp1/Sp3. E(2) also induced promoter-associated acetylation of H3 and H4. These findings demonstrate that an E(2)/ERalpha, Sp1, and C/EBPbeta complex with recruitment of coactivators and TFIIB and Pol II are required for E(2)-activated transcriptional expression of the hPRLR through PIII. Estradiol produced in breast stroma and adipose tissue, which are major sources of estrogen in post-menopausal women, could up-regulate hPRLR gene expression and stimulate breast tumor growth.

Ligand-independent homo- and heterodimerization of human prolactin receptor variants: inhibitory action of the short forms by heterodimerization

Prolactin (PRL) acts through the long form (LF) of the human PRL receptor (hPRLR) to cause differentiation of mammary epithelial cells through activation of the Janus kinase-2 (JAK2)/signal transducer and activator of transcription 5 (STAT5) pathway and subsequent transcriptional events. To determine whether the inhibitory action of hPRLR short forms (SFs; S1a and S1b) on PRL-induced signal transduction through the LF results from heterodimerization, we studied complex formation among variant forms of the hPRLR. 3'-Tagged fusion constructs, with activities comparable to the wild-type species, were used to investigate homodimer and heterodimer formation. The LF and both SFs of the hPRLR formed homodimers under nonreducing conditions, independently of PRL, but formed only monomers under reducing conditions. Coimmunoprecipitation of the cotransfected LF with the SFs (S1a or S1b) in transfected cells showed ligand-independent heterodimerization of individual SFs with the LF. Bioluminescence resonance energy transfer analysis demonstrated homo- and heterodimeric associations of hPRLR variants in human embryonic kidney 293 cells. Biotin-avidin immunoprecipitation analysis revealed that hPRLR forms are cell surface receptors and that SFs do not influence the steady state or half-life of the LF. Significant homo- and heterodimerization of biotinylated membrane hPRLR forms was observed. These findings indicate that homo- and heterodimers of hPRLR are constitutively present, and that the bivalent hormone acts on the preformed LF homodimer to induce the active signal transduction configuration. Although SF homodimers and their heterodimers with LF mediate JAK2 activation, the SF heterodimer partner lacks cytoplasmic sequences essential for activation of the JAK2/signal transducer and activator of transcription 5 pathway. This prevents the heterodimeric LF from mediating activation of PRL-induced genes.

Endogenous human prolactin and not exogenous human prolactin induces estrogen receptor alpha and prolactin receptor expression and increases estrogen responsiveness in breast cancer cells

Prolactin (PRL) and estrogen act synergistically to increase mammary gland growth, development, and differentiation. Based on their roles in the normal gland, these hormones have been studied to determine their interactions in the development and progression of breast cancer. However, most studies have evaluated only endocrine PRL and did not take into account the recent discovery that PRL is synthesized by human mammary cells, permitting autocrine/paracrine activity. To examine the effects of this endogenous PRL, we engineered MCF7 cells to inducibly overexpress human prolactin (hPRL). Using this Tet-On MCF7hPRL cell line, we studied effects on cell growth, PRLR, ER alpha, and PgR levels, and estrogen target genes. Induced endogenous hPRL, but not exogenous hPRL, increased ER alpha levels as well as estrogen responsiveness in these cells, suggesting that effects on breast cancer development and progression by estrogen may be amplified by cross-regulation of ER alpha levels by endogenous hPRL. The long PRLR isoform was also upregulated by endogenous, but not exogenous PRL. This model will allow investigation of endogenous hPRL in mammary epithelial cells and will enable further dissection of PRL effects on other hormone signaling pathways to determine the role of PRL in breast cancer.

Inhibition of prolactin (PRL)-induced proliferative signals in breast cancer cells by a molecular mimic of phosphorylated PRL, S179D-PRL

Posttranslational modifications of prolactin (PRL), including phosphorylation, vary with physiologic state and alter biologic activity. In light of the growing evidence for a role for PRL in proliferation in mammary cancer, we examined the ability of a mimic of phosphorylated human PRL, S179D-PRL, to initiate signals to several pathways in mammary tumor cells alone and in combination with unmodified PRL. Unmodified PRL employed multiple pathways to increase cellular proliferation and cyclin D1 levels in PRL-deficient MCF-7 cells. S179D-PRL was a weak agonist compared with unmodified PRL with regard to cellular proliferation, cyclin D1 levels, and phosphorylation of signal transducer and activator of transcription 5 and ERKs. However, S179D-PRL was a potent antagonist of unmodified PRL to these endpoints. In contrast to the reduced levels of the long isoform of the PRL receptor observed in response to a 3-d incubation with unmodified PRL, S179D-PRL up-regulated expression of this isoform, 4-fold. These studies support the utility of this mutant as a PRL antagonist to proliferative signals in mammary epithelial cells, including a potential role in breast cancer therapeutics.

Estradiol stimulates expression of two human prolactin receptor isoforms with alternative exons-1 in T47D breast cancer cells

Human prolactin receptor (hPRLR) expression is regulated by estradiol-17beta (E(2)) in vivo in animal tissues, and in vitro in normal human endometrial cells and in MCF7 human breast cancer cells. The objective of this study was to determine the effect of E(2) on the expression of two recently described hPRLR isoforms with distinct exons-1, hE1(3) and hE1(N1) that are transcribed from the generic hPIII promoter, also present in the rat and mouse, and the human-specific promoter hP(N1), respectively. Also, to determine the effect of estradiol on the hPIII promoter activity in cancer cells. T47D breast cancer cells were examined using quantitative competitive RT-PCR for the level of expression of two alternative non-coding exon-1 transcripts, hE1(3) and hE1(N1) following incubation with E(2) in presence or absence of the E(2) receptor antagonist ICI 182,780. The effects of estradiol were also evaluated in cells transiently transfected with constructs of hPIII promoter luciferase reporter gene. E(2) significantly increased the expression of both hPRLR mRNA transcripts, hE1(3) and hE1(N1). In transfection studies E(2) activated the hPIII promoter. This effect of estradiol was markedly inhibited by coincubation with the E(2) receptor antagonist. Our results demonstrate a stimulatory effect of estradiol on the expression of hPRLR mRNA species with alternative exons-1, hE1(3) and hE1(N1) possibly through activation of their corresponding promoters. The lack of a formal ERE in these promoters suggested that the effect of estradiol is mediated through association of the activated ER with relevant DNA binding transfactor(s). These findings support the role of E(2) in the regulation of hPRLR expression in human breast cancer cell lines.

Dopamine as a prolactin (PRL) inhibitor

Dopamine is a small and relatively simple molecule that fulfills diverse functions. Within the brain, it acts as a classical neurotransmitter whose attenuation or overactivity can result in disorders such as Parkinson's disease and schizophrenia. Major advances in the cloning and characterization of biosynthetic enzymes, transporters, and receptors have increased our knowledge regarding the metabolism, release, reuptake, and mechanism of action of dopamine. Dopamine reaches the pituitary via hypophysial portal blood from several hypothalamic nerve tracts that are regulated by PRL itself, estrogens, and several neuropeptides and neurotransmitters. Dopamine binds to type-2 dopamine receptors that are functionally linked to membrane channels and G proteins and suppresses the high intrinsic secretory activity of the pituitary lactotrophs. In addition to inhibiting PRL release by controlling calcium fluxes, dopamine activates several interacting intracellular signaling pathways and suppresses PRL gene expression and lactotroph proliferation. Thus, PRL homeostasis should be viewed in the context of a fine balance between the action of dopamine as an inhibitor and the many hypothalamic, systemic, and local factors acting as stimulators, none of which has yet emerged as a primary PRL releasing factor. The generation of transgenic animals with overexpressed or mutated genes expanded our understanding of dopamine-PRL interactions and the physiological consequences of their perturbations. PRL release in humans, which differs in many respects from that in laboratory animals, is affected by several drugs used in clinical practice. Hyperprolactinemia is a major neuroendocrine-related cause of reproductive disturbances in both men and women. The treatment of hyperprolactinemia has greatly benefited from the generation of progressively more effective and selective dopaminergic drugs.

Isolation and characterization of two novel forms of the human prolactin receptor generated by alternative splicing of a newly identified exon 11

We have identified a novel exon 11 of the human prolactin receptor (hPRLR) gene that is distinct from its rodent counterparts and have demonstrated the presence of two novel short forms of the hPRLR (S1(a) and S1(b)), which are derived from alternative splicing of exons 10 and 11. S1(a) encodes 376 amino acids (aa) that contain partial exon 10 and a unique 39-aa C-terminal region encoded by exon 11. S1(b) encodes 288 aa that lack the entire exon 10 and contains 3 amino acids at the C terminus derived from exon 11 using a shifted reading frame. These short forms, which were found in several normal tissues and in breast cancer cell lines, were expressed as cell surface receptors and possessed binding affinities comparable with the long form. Unlike the long form, neither short form was able to mediate the activation of the beta-casein gene promoter induced by prolactin. Instead they acted as dominant negative forms when co-expressed with the long form in transfected cells. Due to a marked difference in the cellular levels between the two short forms in transfected cells, S1(b) was more effective in inhibiting the prolactin-induced activation of the beta-casein gene promoter mediated by the long form of the receptor. The low cellular level of S1(a) was due to its more rapid turnover than the S1(b) protein. This is attributable to specific residues within the C-terminal unique 39 amino acids of the S1(a) form and may represent a new mechanism by which the hPRLR is modulated at the post-translational level. Since both short forms contain abbreviated cytoplasmic domains with unique C termini, they may also exhibit distinct signaling pathways in addition to modulating the signaling from the long form of the receptor. These receptors may therefore play important roles in the diversified actions of prolactin in human tissues.

Prolactin receptors are expressed and hormonally regulated in rat Sertoli cells

In this study, the protein and mRNA expression of the short and long forms of Prolactin (PRL) receptors (PRL-R) were examined by means of Northern and Western blotting analyses in rat testicular Sertoli cells. Transcripts for the short and long forms of PRL-R were detected with specific probes, five major mRNA species of about 1.9, 2.6, 3.0, 3.7 and 5 kb for the short form and two of about 10 and 1.3 kb for the long form. Under reducing conditions, the use of a specific antibody for the short form revealed a major molecular species of approximately 45 kDa. Two groups of molecular species were detected for the long form, several bands with high molecular masses (110-300 kDa) and others about 45-60 kDa. Finally, the expression of the long form of PRL-R was shown to be hormonally regulated as it was inhibited by follicle stimulating hormone (FSH) (ED50 = 5 ng/ml). Together, the localisation of PRL receptors to Sertoli cells as well as the regulatory action of FSH on these receptors suggest that PRL and or (a) PRL-like activity(ies) might be considered as (a) potential regulator(s) of spermatogenesis.

Transcriptional regulation of the generic promoter III of the rat prolactin receptor gene by C/EBPbeta and Sp1

Three promoters are operative in the rat prolactin receptor gene as follows: promoter I (PI) and II (PII) are specific for the gonads and liver, respectively, and promoter III (PIII) is common to several tissues. To investigate the mechanisms controlling the activity of promoter III, its regulatory elements and transcription factors were characterized in gonadal and non-gonadal cells. The TATA-less PIII domain was localized to the region -437 to -179 (ATG +1) containing the 5'-flanking region and part of the non-coding first exon. Within the promoter domain, a functional CAAT-box/enhancer binding protein (C/EBP) (-398) and an Sp1 element (-386), which bind C/EBPbeta and Sp1/Sp3, respectively, contribute individually to promoter activation in gonadal and non-gonadal cells. However, significant redundancy was demonstrated between these elements in non-gonadal cells. Additionally, an element within the non-coding exon 1 (-338) is also required for promoter activity. Activation of PIII by the widely expressed Sp1 and C/EBPbeta factors explains its common utilization in multiple tissues. Moreover, whereas the rat and mouse PIII share similar structure and function, the mouse PI lacks the functional SF-1 element and hence is inactive. These findings indicate that promoter III is of central importance in prolactin receptor gene transcription across species.