The role of small glutamine-rich tetratricopeptide repeat containing protein alpha in female reproductive tissues.

Small glutamine-rich tetratricopeptide repeat containing protein alpha (SGTA) is an evolutionarily conserved protein that functions as a mediator of intracellular protein transport. In particular, SGTA has been shown to act as a co-chaperone protein that promotes cytoplasmic retention of the androgen receptor (AR) and thus acts to modulate AR transcriptional activity. Androgens and the AR are known to be essential for the developmental and physiological processes of male reproductive tissues and the potential importance of SGTA in male tissues has been highlighted by the reduced expression of SGTA relative to AR in metastatic prostate cancer. Although the direct actions of androgens in female reproductive tissues are not well understood, there is increasing interest due to the association of androgen levels with several aspects of female health. In females, the AR is expressed in all reproductive tissues, including the ovary and uterus. Therefore, if present in these female tissues, SGTA could feasibly have implications for the regulation of AR action. In support of this concept, recent genetic studies have identified polymorphisms in the SGTA gene that are associated with increased risk of developing polycystic ovary syndrome (PCOS), a disorder characterised by hyperandrogenism. To date, the expression and function of SGTA in female reproductive tissues has not previously been investigated. Therefore, the overall objective of this thesis was to examine the potential role of SGTA in female reproductive tissues with the following specific aims: a) compare expression and localisation of SGTA and AR, b) ascertain whether SGTA is altered in select female reproductive diseases, and c) determine whether SGTA is able to influence AR subcellular localisation and subsequent action. The results demonstrated that SGTA was evident in the cytoplasm of the epithelial cells of the ovary, Fallopian tube, endometrium, and placenta. Moreover, AR expression was evident in those cells that expressed SGTA, suggesting that the two proteins may interact to influence androgen action as in male tissues. A novel finding of this study, that contravenes the theory of SGTA as an epithelial-specific protein in reproductive tissues, was the detection of SGTA protein in the mesenchymal-derived thecal cells of the ovary. This was further supported by similar expression in the Leydig cells of the testes, which are derived from a common mesenchymal origin. Quantitative analysis of SGTA protein levels did not reveal any difference between normal and pathologic states of the ovary. However, AR protein levels were significantly reduced in ovarian cancer tissues. As a result, the AR:SGTA ratio was significantly reduced, suggesting that genomic AR activity would be negatively impacted in the ovarian epithelial cancer cells. Using several ovarian cancer cell lines in this thesis it was demonstrated that knockdown of SGTA resulted in nuclear localisation of the AR in the absence of androgen hormone. Knockdown of AR resulted in an inhibition of ovarian cancer cell viability, which suggests AR is important in the growth of ovarian cancer cells. However, SGTA knockdown per se had no effect on ovarian cancer cell viability. Furthermore, in this thesis it was demonstrated that knockdown of either AR or SGTA affected expression levels of two genes implicated in ovarian cancer proliferation: distal-less homeobox 5 and calcium-dependent cytosolic phospholipase A₂, raising the possibility of non-genomic actions that remain to be elucidated. In conclusion, the results of this thesis support a role for SGTA in regulating AR action in female reproductive tissues and show that SGTA may influence the pathology of ovarian cancer, but the precise mechanisms remain to be resolved. The information presented in this thesis provides the basis for further investigations to evaluate the role of SGTA in female reproductive tissues.Thesis (Ph.D.) -- University of Adelaide, School of Medicine, 201