NCBI Summary:
The protein encoded by this gene is a member of the dual specificity protein phosphatase subfamily. These phosphatases inactivate their target kinases by dephosphorylating both the phosphoserine/threonine and phosphotyrosine residues. They negatively regulate members of the mitogen-activated protein (MAP) kinase superfamily (MAPK/ERK, SAPK/JNK, p38), which are associated with cellular proliferation and differentiation. Different members of the family of dual specificity phosphatases show distinct substrate specificities for various MAP kinases, different tissue distribution and subcellular localization, and different modes of inducibility of their expression by extracellular stimuli. This gene product inactivates ERK2, is expressed in a variety of tissues with the highest levels in heart and pancreas, and unlike most other members of this family, is localized in the cytoplasm. Mutations in this gene have been associated with congenital hypogonadotropic hypogonadism. Alternatively spliced transcript variants have been found for this gene. [provided by RefSeq, Jan 2014]
General function
Enzyme
Comment
Cellular localization
Cytoplasmic
Comment
Ovarian function
Ovulation
Comment
How Protein Kinase A Activates Canonical Tyrosine Kinase Signaling Pathways to Promote Granulosa Cell Differentiation. Law NC et al. (2017) Protein kinase A (PKA) has recently been shown to mimic the actions of follicle-stimulating hormone (FSH) by activating signaling pathways that promote granulosa cell (GC) differentiation, such as phosphatidylinositol 3-kinase (PI3K) and mitogen activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK). We sought to elucidate the mechanism by which PKA, a Ser/Thr kinase, intersected the PI3K/AKT and MAPK/ERK pathways that are canonically activated by receptor tyrosine kinases (RTKs). Our results show that for both of these pathways, the RTK is active in the absence of FSH yet signaling down the pathways to commence transcriptional responses requires FSH-stimulated PKA activation. For both pathways, PKA initiates signaling by regulating the activity of a protein phosphatase. For the PI3K/AKT pathway, PKA activates the Ser/Thr protein phosphatase PP1 complexed with the insulin-like growth factor 1 receptor (IGF1R) and insulin receptor substrate 1 (IRS1) to dephosphorylate Ser residues on IRS1, authorizing phosphorylation of IRS1 by the IGF1R to activate PI3K. Treatment of GCs with FSH and exogenous IGF1 initiates synergistic IRS1 Tyr phosphorylation and resulting gene activation. The mechanism by which PKA activates PI3K is conserved in preovulatory GCs, MCF7 breast cancer cells, and FRTL thyroid cells. For the MAPK/ERK pathway, PKA promotes inactivation of the MAPK phosphatase (MKP) dual specificity phosphatase (DUSP) MKP3/DUSP6 to permit MEK-phosphorylated ERK to accumulate downstream of the epidermal growth factor receptor. Thus, for the two central signaling pathways that regulate gene expression in GCs, FSH via PKA intersects canonical RTK-regulated signaling by modulating the activity of protein phosphatases.//////////////////
Follicle-Stimulating Hormone (FSH) Dependent Regulation of Extracellular Regulated Kinase (ERK) Phosphorylation by MAP kinase phosphatase MKP3. Donaubauer EM et al. (2016) Within the ovarian follicle, granulosa cells (GCs) surround and support immature oocytes. Follicle-stimulating hormone (FSH) promotes differentiation and proliferation of GCs and is essential for fertility. We recently reported that ERK activation is necessary for FSH to induce key genes that define the preovulatory GC. This research focused on the phospho-regulation by FSH of ERK within GCs. FSH-stimulated ERK phosphorylation on Thr202/Tyr204 was PKA-dependent but MEK(Ser217/Ser220) phosphorylation was not regulated; rather, MEK was already active. Yet, treatment of GCs with EGFR inhibitor AG1487, a dominant-negative RAS, a SH2-domain containing Tyr phosphatase inhibitor NSC 87877, or the MEK inhibitor PD98059 blocked FSH-dependent ERK(Thr202/Tyr204) phosphory-lation, demonstrating the requirement for upstream pathway components. We hypothesized that FSH via PKA enhances ERK phosphorylation by inhibiting the activity of a protein phosphatase that constitutively dephosphorylates ERK in the absence of FSH, allowing MEK-phosphorylated ERK to accumulate in the presence of FSH due to inactivation of the phosphatase. GCs treated with different phosphatase inhibitors permitted elimination of both Ser/Thr and Tyr phosphatases, and implicated dual specificity phosphatases (DUSPs) in the dephosphorylation of ERK. Treatment with MAP kinase phosphatase (MKP3)(DUSP6) inhibitors increased ERK(Thr202/Tyr204) phosphorylation in the absence of FSH to levels comparable to ERK phosphorylated in the presence of FSH. ERK co-immunoprecipitated with Myc-Flag-tagged MKP3(DUSP6). GCs treated with MKP3(DUSP6) inhibitors blocked or PKA inhibitors enhanced dephosphorylation of recombinant ERK2-GST in an in vitro phosphatase assay. Together these results suggest that FSH-stimulated ERK activation in GCs requires the PKA-dependent inactivation of MKP3(DUSP6).//////////////////
Expression regulated by
FSH, LH, FGF2
Comment
Dual-specificity phosphatase 6 (DUSP6) mRNA and protein abundance is regulated by fibroblast growth factor 2 in sheep granulosa cells and inhibits c-Jun N-terminal kinase (MAPK8) phosphorylation. Relav L et al. (2021) Growth factors regulate ovarian follicle development and they signal through intracellular pathways including mitogen-activated protein kinase (MAPK) phosphorylation, which is negatively regulated by a subfamily of 23 dual-specificity phosphatases (DUSP). Using sheep granulosa cells as a model, we detected mRNA encoding 16 DUSPs in vivo and in vitro. Stimulation of cells in vitro with FGF2 increased (p < 0.05) abundance of DUSP1, DUSP2, DUSP5 and DUSP6 mRNA, and abundance of DUSP1 and DUSP6 proteins (p < 0.05). In contrast, neither FGF8b nor FGF18 had any major effect on DUSP mRNA abundance. Inhibition of DUSP6 action with the inhibitor BCI significantly increased (p < 0.05) MAPK8 (JNK) phosphorylation but not phosphoMAPK14 (p38) or MAPK3/1 (ERK1/2) abundance. This study suggests that FGFs stimulate DUSP protein abundance, that DUSP6 regulates MAPK8 phosphorylation in granulosa cells, and DUSPs are involved in the differential MAPK signaling of individual FGF ligands.//////////////////
Ovarian localization
Granulosa, Theca
Comment
Identification and Characterization of Five Genes Induced by hCG Administration during the Preovulatory Period in the Rat Ovary.
Misung Jo, 2004 .
The LH surge initiates the ovulatory process by triggering a series of biochemical and molecular events that induce the spatiotemporal expression of specific genes. In the present study, we utilized a newly developed rat ovarian gene expression database (rOGED) to identify unknown genes involved in the ovulatory process. Five genes that showed elevated levels of mRNA expression after hCG treatment in rOGED were selected. These genes included mitogen-activated protein kinase phosphotase-3 (MKP-3), runt related transcription factor (Runx 1), calgranulin B, 1-macroglobulin, and synaptosome-associated protein 25 kDa (Snap 25). To confirm and characterize the spatiotemporal expression pattern of these genes during the periovulatory period, immature rats were injected with PMSG; 48 h later hCG was administered. Ovaries were collected at 0 (48 h post-eCG), 6, 12, and 24 h post-hCG. Northern blots revealed dramatic, yet transient increases in levels of mRNA for Runx 1, calgranulin B, MKP-3, and 1-macroglobulin at 6 h post-hCG, which are consistent with the profiles seen in rOGED. Two transcripts of the Snap 25 gene were detected, which were expressed differentially after hCG injection. In situ hybridization showed a distinct localization pattern of expression of these genes. High expression of both Runx 1 and MKP-3 was localized to the granulosa cell layer of preovulatory follicles at 6 and 12 h post-hCG, but the expression was also detected in the theca layer at 6 h post-hCG. MKP-3 can inactivate ERKs while Runx 1 is involved in the cell differentiation/ proliferation process. Snap 25 mRNA was localized to granulosa cells of preovulatory follicles and the theca layer at 12 h post-hCG. Snap 25 is a key component of SNARE proteins required for intracellular membrane fusion events during exocytosis. 1-Macroglobulin can inhibit a broad spectrum of proteases and was localized only to the theca layer at 6 h post-hCG. Calgranulin B mRNA was localized to cells scattered in the interstitial and stroma layer of ovaries obtained at 6 h and 12 h post-hCG, but not to follicular cells. Calgranulin B is highly expressed in neutrophils and monocytes that are found in a variety of inflammatory conditions. The fact that the ovulatory hCG stimulus induces dramatic, yet transient increases in levels of mRNA for these genes in a cell-type specific manner suggests that the expression of each of these genes may be important for successful ovulation.
Follicle stages
Antral, Preovulatory
Comment
Selective expression of KrasG12D in granulosa cells of the mouse ovary causes defects in follicle development and ovulation. Fan HY et al. Activation of the RAS family of small G-proteins is essential for follicle stimulating hormone-induced signaling events and the regulation of target genes in cultured granulosa cells. To analyze the functions of RAS protein in granulosa cells during ovarian follicular development in vivo, we generated conditional knock-in mouse models in which the granulosa cells express a constitutively active Kras(G12D). The Kras(G12D) mutant mice were subfertile and exhibited signs of premature ovarian failure. The mutant ovaries contained numerous abnormal follicle-like structures that were devoid of mitotic and apoptotic cells and cells expressing granulosa cell-specific marker genes. Follicles that proceeded to the antral stage failed to ovulate and expressed reduced levels of ovulation-related genes. The human chorionic gonadotropin-stimulated phosphorylation of ERK1/2 was markedly reduced in mutant cells. Reduced ERK1/2 phosphorylation was due, in part, to increased expression of MKP3, an ERK1/2-specific phosphatase. By contrast, elevated levels of phospho-AKT were evident in granulosa cells of immature Kras(G12D) mice, even in the absence of hormone treatments, and were associated with the progressive decline of FOXO1 in the abnormal follicle-like structures. Thus, inappropriate activation of KRAS in granulosa cells blocks the granulosa cell differentiation pathway, leading to the persistence of abnormal non-mitotic, non-apoptotic cells rather than tumorigenic cells. Moreover, those follicles that reach the antral stage exhibit impaired responses to hormones, leading to ovulation failure. Transient but not sustained activation of RAS in granulosa cells is therefore crucial for directing normal follicle development and initiating the ovulation process.