Small glutamine-rich tetratricopeptide repeat-containing protein alpha (SGTA), a candidate gene for polycystic ovary syndrome

M.O. Goodarzi 0 1 2 4 N. Xu 2 J. Cui 0 X. Guo 0 Y.I. Chen 0 1 4 R. Azziz 1 3 4 0 Medical Genetics Institute, Cedars-Sinai Medical Center , Los Angeles, CA 90048 , USA 1 Department of Obstetrics and Gynecology, Center for Androgen Related Disorders, Cedars-Sinai Medical Center , Los Angeles, CA 90048 , USA 2 Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Cedars-Sinai Medical Center , Los Angeles, CA 90048 , USA 3 Department of Obstetrics and Gynecology, the David Geffen School of Medicine at UCLA , Los Angeles, CA 90095 , USA 4 Department of Medicine, the David Geffen School of Medicine at UCLA , Los Angeles, CA 90095 , USA BACKGROUND: Polycystic ovary syndrome (PCOS) is a heterogenic, complex common genetic disease. Multiple pathways are involved in its pathogenesis, including the androgen signaling pathway and insulin signaling pathway. Small glutamine-rich tetratricopeptide repeat-containing protein alpha (SGTA) is a putative member of the androgen receptor - chaperone - co-chaperone complex, and may play a role in androgen signaling as a cochaperone. Polymorphisms in the SGTA gene have not been evaluated for a role in PCOS. METHODS: Women with and without PCOS (287 cases, 187 controls) were genotyped for three single nucleotide polymorphisms (SNPs) in SGTA. SNPs and haplotypes were determined and tested for association with PCOS and component traits of PCOS. RESULTS: For SNP rs1640262, homozygotes for the minor allele were protected against PCOS (P 5 0.009). Haplotype 1 (G - A - T) was associated with increased risk of PCOS (P 5 0.015). In women with PCOS, haplotype 2 (A - G - C) was associated with increased insulin resistance (P 5 0.013), consequently resulting in increased insulin secretion (P 5 0.014). CONCLUSIONS: This study presents genetic evidence suggesting a potential role of SGTA in the pathogenesis of PCOS. SGTA may provide a connection between multiple pathways in PCOS. Introduction Polycystic ovary syndrome (PCOS) is a heterogenic, complex common genetic disease, affecting 6 8% of reproductive age women (Azziz et al., 2004). PCOS is characterized by hyperandrogenism, menstrual dysfunction and polycystic ovarian morphology (Goodarzi and Azziz, 2006). Patients with PCOS may also present with infertility, obesity, insulin resistance and often have a high burden of cardiovascular risk factors. The molecular basis for PCOS is poorly understood. Candidate genes for PCOS have been chosen from logical pathways, such as the insulin signaling pathway or androgen biosynthetic pathway (Franks and McCarthy, 2004; Escobar-Morreale et al., 2005; Nam Menke and Strauss, 2007; Urbanek, 2007). Hypotheses regarding these pathophysiologic pathways have led to the implication of several genes in the development of PCOS. However, since PCOS is a complex common disease, which is likely due to both genetic and environmental factors, more evidence is needed to explain the molecular mechanisms of PCOS. Although the etiology of PCOS remains unknown, most patients with PCOS present with hyperandrogenism. The phenotype of PCOS may have hirsutism and ovulatory dysfunction without significantly increased androgens (Azziz et al., 2006). Up to 25% of PCOS patients have normal levels of circulating androgens, which suggests sensitivity to androgens is increased in this type of PCOS (Chang et al., 2005). Even in those with hyperandrogenemia, the degree of androgen elevation is typically mild. Therefore, components of androgen signaling may play a key role in the pathophysiology of PCOS, in some or all subjects. Unbound androgen receptor (AR) is inactive in the cytoplasm as a large dynamic heterocomplex which is composed of heat shock proteins (such as Hsp70 and Hsp90) and their co-chaperones (Pratt and Toft, 1997). Three main families of co-chaperones include Bag-1 homology (Bcl-2 binding athanogene or Bag domains), DnaJ homology (or J domains) and tetratricopeptide repeat (TPR) containing proteins (Young et al., 2003). The complex of chaperones and their co-chaperones binds to the hormone binding domain of AR, and assists AR to function properly at each step of its functional cycle (Pratt and Toft, 1997). Abnormal function or expression of co-chaperones is proposed to affect AR activity. For example, in tumor cells of prostate cancer, the abnormal Hsp70 and Bag-1L expression in the secretory epithelium enhances transcriptional activity of the AR (Shatkina et al., 2003). This suggests that genes encoding components of the co-chaperone complex can be candidates for study of the androgen signaling pathway, and may further help us understand the role of androgen signaling in conditions such as PCOS. The current study focused on a new candidate gene for PCOSsmall glutamine-rich TPR-containing protein alpha (SGTA), as one of the co-chaperones binding to the AR. It is located on chromosome 19p13, 5.3 MB telomeric to the D19S884 microsatellite implicated by several studies in PCOS susceptibility (Urbanek et al., 1999; Tucci et al., 2001; Urbanek et al., 2005; Stewart et al., 2006). SGTA restrains androgen signaling by holding the AR in the cytoplasm (Buchanan et al., 2007). However, whether SGTA is involved in the pathophysiology of PCOS is not known. Since this gene is expressed ubiquitously in various tissues, this protein may serve a housekeeping function. Alternatively, SGTA may affect multiple processes in addition to androgen signaling, making it a good candidate gene for PCOS, a syndrome characterized by dysfunction in multiple systems. We studied the association between SGTA and PCOS, and investigated its role in androgen- and insulin-related traits in affected women. We analyzed single nucleotide polymorphisms (SNPs) as well as haplotypes in SGTA, to capture common variation across the entirety of the gene. We found that (i) variation in SGTA was associated with PCOS risk and (ii) one of the haplotypes was associated with increased insulin resistance, resulting in increased beta cell function. Materials and Methods Subjects A total of 287 consecutive White patients with PCOS, aged 13 47 years, and 187 healthy White control women, aged 14 60, were recruited from Birmingham, AL, USA. All subjects were unrelated. PCOS subjects were recruited consecutively from the reproductive endocrine practice of one of the investigators (R.A.) at the University of Alabama at Birmingham (UAB). Participation in research studies was offered to patients meeting inclusion criteria (premenopausal, non-pregnant, on no hormonal therapy, including oral contraceptives, for at least 3 months, and meeting diagnostic criteria for PCOS). In order to ensure the inclusion of women with the classic disorder, the presence of PCOS was defined by the 1990 National Institutes of Health consensus criteria (Zawadzki and Dunaif, 1992), including: (i) clinical hyperandrogenism and/or hyperandrogenemia, (ii) oligo-ovulation and (iii) the exclusion of related disorders, including andro (...truncated)