Signal transducer and activator of transcription (STAT) 1 and STAT3 are expressed in the human ovary and have Janus kinase 1-independent functions in the COV434 human granulosa cell line

Ovarian granulosa cells are fundamental for oocyte maintenance and maturation. Recent studies have demonstrated the importance of members of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signalling pathway in the granulosa cell population of mouse and horse ovaries, with perturbation of JAK1 signalling in the mouse shown to impair oocyte maintenance and accelerate primordial follicle activation. The presence and role of the JAK/STAT pathway in human granulosa cells has yet to be elucidated. In this study, expression of JAK1, STAT1 and STAT3 was detected in oocytes and granulosa cells of human ovarian sections from fetal (40 weeks gestation) and premenopausal ovaries (34-41 years of age; n=3). To determine the effects of JAK1 signalling in granulosa cells, the human granulosa-like cell line COV434 was used, with JAK1 inhibition using ruxolitinib. Chemical inhibition of JAK1 in COV434 cells with 100nM ruxolitinib for 72h resulted in significant increases in STAT3 mRNA (P=0.034) and p-Y701-STAT1 protein (P=0.0117), demonstrating a role for JAK1 in modulating STAT in granulosa cells. This study implicates a conserved role for JAK/STAT signalling in human ovary development, warranting further investigation of this pathway in human granulosa cell function.

Janus kinase JAK1 maintains the ovarian reserve of primordial follicles in the mouse ovary

STUDY QUESTION

Is the Janus kinase and signal transducer and activator of transcription (JAK-STAT) signalling pathway involved in ovarian follicle development and primordial follicle activation?

SUMMARY ANSWER

JAK1 is a key factor involved in the regulation of primordial follicle activation and maintenance of the ovarian reserve.

WHAT IS KNOWN ALREADY

A series of integrated, intrinsic signalling pathways (including PI3K/AKT, mTOR and KITL) are responsible for regulating the ovarian reserve of non-growing primordial follicles and ultimately female fertility. The JAK-STAT signal transduction pathway is highly conserved with established roles in cell division and differentiation. Key pathway members (specifically JAK1, STAT3 and SOCS4) have been previously implicated in early follicle development.

STUDY DESIGN, SIZE, DURATION

A laboratory animal study was undertaken using the C57Bl/6 inbred mouse strain as a model for human ovarian follicle development. To determine which Jak genes were most abundantly expressed during primordial follicle activation, mRNA expression was analysed across a developmental time-course, with ovaries collected from female mice at post-natal days 1 (PND1), 4 (PND4), 8 (PND8), as well as at 6 weeks (6WK) and 7 months (7MTH) (n ≥ 4). Functional analysis of JAK1 was performed on PND2 mouse ovaries subjected to in vitro explant culture treated with 12.5 μM Ruxolitinib (JAK inhibitor) or vehicle control (DMSO) for 48 h prior to histological assessment (n ≥ 4).

PARTICIPANTS/MATERIALS, SETTING, METHODS

The expression and localization of the JAK family during ovarian follicle development in the C57Bl/6 inbred mouse strain were evaluated using quantitative PCR, immunoblotting and immunolocalisation. Functional studies were undertaken using the JAK inhibitor Ruxolitinib to investigate the underpinning cellular mechanisms via biochemical in vitro inhibition and histological assessment of intact neonate ovaries. All experiments were replicated at least three times using tissue from different mice unless otherwise stated.

MAIN RESULTS AND THE ROLE OF CHANCE

Jak1 is the predominant Jak mRNA expressed in the C57Bl/6 mouse ovary across all developmental time-points assessed (P ≤ 0.05). Forty-eight hour inhibition of JAK1 with Ruxolitinib of PND2 ovaries in vitro demonstrated concomitant acceleration of primordial follicle activation and apoptosis (P ≤ 0.001) and upregulation of downstream JAK-STAT pathway members STAT3 and suppressors of cytokine signalling 4 (SOCS4).

LARGE-SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Results are shown in one species, the C57Bl/6 mouse strain as an established model of human ovary development. Ruxolitinib also inhibits JAK2, with decreased efficacy. However, Jak2 mRNA had limited expression in the mouse ovary, particularly at the neonatal stages of follicle development, thus any effect of Ruxolitinib on primordial follicle activation was unlikely to be mediated via this isoform.

WIDER IMPLICATIONS OF THE FINDINGS

This study supports a key role for JAK1 in the maintenance and activation of primordial follicles, with potential for targeting the JAK-STAT pathway as a method of regulating the ovarian reserve and female fertility.

STUDY FUNDING AND COMPETING INTEREST(S)

This project has been funded by the Australian National Health and Medical Research Council (G1600095) and The Hunter Medical Research Institute Bob and Terry Kennedy Children's Research Project Grant in Pregnancy & Reproduction (G1501433). All authors declare no conflict of interests.

Prolactin Receptor Isoforms as the Basis of Tissue-Specific Action of Prolactin in the Norm and Pathology

The review describes functional and structural features of different isoforms of prolactin receptor, mechanisms of signaling pathway activation, and molecular messengers involved in the transmission and termination of signal from the prolactin receptor isoforms. Changes in the ratio between prolactin receptor isoforms, key mediators of prolactin signal transduction and termination in various organs and tissues, are analyzed. Special attention is given to the role of molecular mediators and the ratio between the isoforms in normal physiological functions and pathologies. Approaches for therapeutic correction of prolactin signaling impairments are discussed.

Regulation of cytokine-inducible SH2-containing protein (CIS) by ubiquitination and Elongin B/C interaction

Cytokine-inducible SH2-containing protein (CIS) inhibits prolactin receptor (PRLR) signaling and acts as part of an E3 ubiquitin ligase complex through interactions with Elongin B/C proteins. This study aimed to identify CIS lysine ubiquitination sites and determine roles of ubiquitination and Elongin B/C interactions on CIS protein stability and PRLR signaling inhibition. Site-directed mutations revealed that CIS can be ubiquitinated on all six lysine residues. Elongin B/C interaction box mutation had no influence on CIS ubiquitination. CIS stability was increased by mutation of lysine residues and further enhanced by co-mutation of Elongin B/C interaction domain. CIS inhibition of STAT5B phosphorylation and casein promoter activation was dependent on CIS interactions with Elongin B/C, but not on CIS ubiquitination. These data indicate CIS protein stability is regulated through multiple mechanisms, including ubiquitination and interaction with Elongin B/C proteins, whereas CIS functional inhibition of PRLR signaling is dependent on the Elongin B/C interaction.

The transcription factor Ap-1 regulates monkey 20α-hydroxysteroid dehydrogenase promoter activity in CHO cells

Background

Monkey 20α-hydroxysteroid dehydrogenase (20α-HSD) is a catabolic enzyme responsible for converting progesterone into biologically inactive 20α-hydroxyprogesterone, thereby playing a key role in the estrous cycle or pregnancy and allowing ovulation and parturition to occur in most mammalian animals. Monkey 20α-HSD was highly abundant in ovarian and placental tissues during the pre-ovulation and pre-parturition phase and was primarily localized in the syncytiotrophoblast of the placenta. In this study, we focused on the molecular characterization of the monkey 20α-HSD promoter region by conducting reporter assays in Chinese hamster ovary (CHO) K1 cells.

Results

A reporter assay using constructs of various lengths of the 5′-flanking region (-890-Luc, -513-Luc, -306-Luc, -273-Luc, and -70-Luc) revealed that a region corresponding to the activator protein 1 (Ap-1) located between -281 and -274 bp was essential for the transcriptional activity. Absence of the Ap-1 site in -273-Luc dramatically decreased the transcription levels to the control levels. When the reporter constructs were co-transfected with Ap-1 (Jun) and specificity protein (Sp-1) genes, the transcription activities of the constructs increased with the exception of -273 and -70, while that of the double construct was reduced compared to that of Ap-1 alone. Furthermore, mutational analysis demonstrated that a putative Ap-1 site played an important role in the expression of the reporter gene. These findings were confirmed by EMSA examining the interactions of the protein Ap-1 in a nuclear extract from CHO-K1 cells and the expression levels of the Ap-1 transcription factor in pre-parturition placenta and CHO-K1 cells. Although mut-1 and mut-2 of Ap-1 bound with nuclear extracts from CHO-K1 cells, the transcriptional activity of mut-3 was almost completely suppressed.

Conclusions

Our results indicate that the Ap-1 site (-281 → -274) (5′-TGTCTCAT-3′) plays a crucial role in the activation of the monkey 20α-HSD gene. Thus, we demonstrated that monkey 20α-HSD promoter activity is regulated by the transcription factor Ap-1 in CHO-K1 cells.

Reversible infertility in a liver receptor homologue-1 (LRH-1)-knockdown mouse model

Liver receptor homologue-1 (LRH-1) is an orphan nuclear receptor that has been implicated in steroid hormone biosynthesis and fertility. Herein we describe a transgenic inducible short hairpin (sh) RNA mouse model that was used to study the effect of transient LRH-1 knockdown in vivo. Induction of expression of the shRNA directed against LRH-1 for 2–6 weeks resulted in 80% knockdown of LRH-1 protein in the ovary and complete infertility. Gonadotropin hyperstimulation could not rescue the observed defects in ovulation and corpus luteum formation in LRH-1-knockdown mice. The infertility phenotype was fully reversible because LRH-1-knockdown females became pregnant and delivered normal size litters and healthy pups after cessation of LRH-1 shRNA expression. Timed ovarian microarray analysis showed that, in line with the observed decrease in plasma progesterone levels, key steroid biosynthesis genes, namely Star, Cyp11a1, Hsd3b and Scarb1, were downregulated in LRH-1-knockdown ovaries. In contrast with what has been described previously, no clear effect was observed on oestrogenic activity in LRH-1-knockdown mice. Only Sult1e1 and, surprisingly, Hsd17b7 expression was modulated with potentially opposite effects on oestradiol bioavailability. In conclusion, the fully reversible infertility phenotype of LRH-1-knockdown mice shows the feasibility of an LRH-1 antagonist as new contraceptive therapy with a mechanism of action that most prominently affects cholesterol availability and progesterone production.

Ovarian signalling pathways regulated by leptin during the ovulatory process

Leptin, a protein secreted by different tissues, is able to exert both stimulatory and inhibitory effects on the ovulatory process. Thus, we investigated whether these opposite effects involve changes in the ovarian signalling pathways in response to different levels of leptin. To this end, we performed both in vivo and in vitro assays using immature rats primed with gonadotrophins to induce ovulation. The acute treatment with leptin, which inhibits the ovulatory process, caused a significant decrease in the phosphorylation of both STAT3 and ERK1/2 and a simultaneous increase in suppressors of cytokine signalling 3 (SOCS3) protein. However, daily administration of a low dose of leptin, which induces the ovulatory process, showed increased phosphorylation of both STAT3 and ERK1/2 and a decreased expression of SOCS3 protein. Using ovarian explant cultures, we also found that leptin was able to activate both STAT3 and ERK1/2 at 10 ng/ml but only STAT3 at 300–500 ng/ml. In addition, at 100–300 ng/ml, leptin increased protein but not mRNA expression of SOCS3. The addition of specific inhibitors of JAK/STAT and MAPK signalling pathways suppressed both the increase and the decrease in leptin-induced progesterone secretion. These results indicate that i) different levels of leptin are able to regulate STAT3, ERK1/2 and SOCS3 at both intra- and extra-ovarian level and that ii) the dual action of leptin on steroidogenesis seems to occur, at least in part, through both the ERK and STAT cascades.

SOCS3-mediated blockade reveals major contribution of JAK2/STAT5 signaling pathway to lactation and proliferation of dairy cow mammary epithelial cells in vitro

Suppressor of cytokine signaling 3 (SOCS3) is a cytokine-induced negative feedback-loop regulator of cytokine signaling. More and more evidence has proved it to be an inhibitor of signal transducers and activators of transcription 5 (STAT5). Here, we used dairy cow mammary epithelial cells (DCMECs) to analyze the function of SOCS3 and the interaction between SOCS3 and STAT5a. The expression of SOCS3 was found in cytoplasm and nucleus of DCMECs by fluorescent immunostaining. Overexpression and inhibition of SOCS3 brought a remarkable milk protein synthesis change through the regulation of JAK2/STAT5a pathway activity, and SOCS3 expression also decreased SREBP-1c expression and fatty acid synthesis. Inhibited STAT5a activation correlated with reduced SOCS3 expression, which indicated that SOCS3 gene might be one of the targets of STAT5a activation, DCMECs treated with L-methionine (Met) resulted in a decrease of SOCS3 expression. SOCS3 could also decrease cell proliferation and viability by CASY-TT detection. Together, our findings indicate that SOCS3 acts as an inhibitor of JAK2/STAT5a pathway and disturbs fatty acid synthesis by decreasing SREBP-1c expression, which validates its involvement in both milk protein synthesis and fat synthesis. In aggregate, these results reveal that low SOCS3 expression is required for milk synthesis and proliferation of DCMECs in vitro.

Suppressor of cytokine signaling 4 (SOCS4): moderator of ovarian primordial follicle activation

Mammalian ovarian primordial follicle activation and regulation is considered as one of the most important stages of folliculogenesis and as such requires exquisite control. Selection of quiescent follicles to enter the growing pool determines the rate of supply of maturing follicles over the female reproductive lifespan. To coordinate this process a range of positive and negative input signals contribute to determine follicle fate. This study demonstrates that the cytokine Leukemia Inhibitory Factor (LIF) activates the Janus Kinase 1/Signal Transducers and Activators of Transcription 3 (JAK1/STAT3) signaling pathway in pre-granulosa cells and positively regulates primordial follicle activation. Negative regulation of the JAK/STAT pathway is controlled by the suppressor of cytokine signaling 4 (SOCS4) protein, which target members of negative feedback loops, Cardiotrophin like Cytokine (CLC), Poly (rC) Binding Protein 1 (PCBP1), and Cytosolic Malate Dehydrogenase (MDH1) to suppress follicle growth and development.