LATS1 phosphorylates forkhead L2 and regulates its transcriptional activity

Abstract

is expressed in the ovary and acts as a transcriptional repressor of the steroidogenic acute regulatory (StAR) gene, a marker of granulosa cell differentiation. Human FOXL2 mutations that produce truncated proteins lacking the COOH terminus result in blepharophimosis/ptosis/epicanthus inversus (BPES) syndrome type I, which is associated with premature ovarian failure (POF). In this study, we investigated whether FOXL2's activity as a transcriptional repressor is regulated by phosphorylation. We found that FOXL2 is phosphorylated at a serine residue and, using yeast two-hybrid screening, identified LATS1 as a potential FOXL2-interacting protein.LATS1 is a serine/threonine kinase whose deletion in mice results in an ovarian phenotype similar to POF. Using coimmunoprecipitation and kinase assays, we confirmed that LATS1 binds to FOXL2 and demonstrated that LATS1 phosphorylates FOXL2 at a serine residue. Moreover, we found that FOXL2 and LATS1 are coexpressed in developing mouse gonads and in granulosa cells of small and medium follicles in the mouse ovary. Last, we demonstrated that coexpression with LATS1 enhances FOXL2's activity as a repressor of the StAR promoter, and this results from the kinase activity of LATS1. These results provide novel evidence that FOXL2 is phosphorylated by LATS1 and that this phosphorylation enhances the transcriptional repression of the StAR gene, a marker of granulosa cell differentiation. These data support our hypothesis that phosphorylation of FOXL2 may be a control mechanism regulating the rate of granulosa cell differentiation and hence, follicle maturation, and its dysregulation may contribute to accelerated follicular development and POF in BPES type I. large tumor suppressor gene 1 phosphorylation; transcriptional regulation; forkhead L2; granulosa cell; premature ovarian failure PREMATURE OVARIAN FAILURE (POF) is defined as a condition causing amenorrhea, hypoestrogenism, and elevated gonadotropins in women under 40 yr of age (1) and can be associated with failure to endow the follicle pool or an early loss of the fixed follicle pool following excess follicle recruitment and/or atresia. A genetic basis for selective cases of POF has been determined. Patients with blepharophimosis-ptosis-epicanthus inversus (BPES) syndrome type I exhibit POF in association with characteristic eyelid dysplasia, blepharophimosis, ptosis, and epicanthus inversus (60). Ovaries from BPES type I patients are histologically variable, ranging from the presence of some primordial follicles with atretic follicles to complete absence of follicles and scarring of the ovaries (23). The gene encoding the transcription factor forkhead L2 (FOXL2) (15) maps to the BPES locus on chromosome 3q22-3q23. FOXL2 is a member of the forkhead/hepatocyte nuclear factor 3 family of transcription factors (15), which is characterized by the presence of a conserved winged helix domain that is essential for DNA binding as well as more divergent transactivation or transrepression domains (12,29,33). FOXL2 mutations in indivi...

Hippo Signaling Pathway Reveals a Spatio-Temporal Correlation with the Size of Primordial Follicle Pool in Mice

“…Although Chen et al confirmed that YAP1 appears to be a new susceptibility gene for PCOS in Han Chinese women [49], we cannot exclude more localized changes in Hippo genes expression at the cellular level. Furthermore, LATS1 phosphorylated forkhead L2 (FOXL2) and regulated its transcriptional activity in some ovary of primary ovarian insufficient POI patients [50,51]. In this study, our results also confirmed that the Hippo signal pathway relates with the maturation of mammalian oocytes, proliferation of granulosa cells and follicular atresia in folliculogenesis.…”

Lats1 Deletion Causes Increased Germ Cell Apoptosis and Follicular Cysts in Mouse Ovaries1

“…Some of these signals could include changes in cell-cell contact, cell density, or cell-extracellular matrix (ECM) interactions [39][40][41]. The Hippo pathway could also interact with well-known regulators of follicular development, such as FOXL2 [42] and members of the TGF-beta family, through interaction with SMAD signaling proteins [43][44][45]. Hippo signaling could also be regulated by secreted paracrine or endocrine factors that act through G-protein coupled receptors: Studies using multiple mammalian cell lines suggest that GPCR-mediated diffusible signals can either up-regulate or down-regulate the activity of YAP1/WWTR1 by acting through Rho GTPase and actin cytoskeleton [46][47][48].…”

Novel action of FOXL2 as mediator of Col1a2 gene autoregulation

“…This differential activity is likely dependent on specific FOXL2 binding partners that constitute the transcriptional complex leading to gene regulation (Fleming et al, 2010; Pisarska et al, 2010, 2011; Georges et al, 2013) as well as post-translational modifications (PTMs) and variant alternative FOXL2 binding sites (see below). A variety of protein binding partners of FOXL2 have been reported, including DEAD box-containing protein (DP103; Lee et al, 2005), SMAD3 (Blount et al, 2009), ER alpha, (Kim et al, 2009), Steroidogenic factor-1 (SF-1; Park et al, 2010), UBC9, PIAS1 (Marongiu et al, 2010), LATS1 (Pisarska et al, 2010), FOXL2 itself (Kuo et al, 2011), CXXC4, CXXC5, CREM, GMEB1, NR2C1, SP100, RPLP1, BANF1, XRCC6, SIRT1 L’Hôte et al, 2012), GSK3β, MDM2 (Kim et al, 2014) and NOBOX (Bouilly et al, 2014). …”

“…As PTMs, sumoylation, phosphorylation and acetylation, have all been shown to modulate FOXL2 activity (Kuo et al, 2009; Marongiu et al, 2010; Pisarska et al, 2010; Georges et al, 2011; Kim et al, 2014). Recent evidence indicates that such modifications can even drive FOX factors to bind to particular target genes in response to environmental signals (Benayoun et al, 2011).…”