br Fig A MTS assay showing
Fig. 5. (A) MTS assay showing the proliferation of PC-3 Oxaliplatin treated with FSH or DHT at concentrations and times indicated. (B) viability assay examined by trypan blue exclusion. The values in MTS are mean § SD of 3 independent experiments.
detected in C4-2 and PC-3 and low in LNCaP cells suggests that the FSH responsiveness may emerge during ADT and facilitate tumor cell growth and resistance to ADT. Con-versely, the absence of FSHR in normal prostatic epithelial cells, PNT1A, shows that the FSHR is exclusively confined to cancer cells, and especially to androgen independent cells. These results were in line with the previously reported studies in humans, in whom FSHR expression was absent in most noncancerous cells, in contrast to malignant ones [11 −13].
Rising serum PSA in patients after ADT indicates relapse and that malignant cell growth is restored in an AR-independent fashion . The significant induction of PSA in the metastatic C4-2 cells is in accordance with the clinical scenario that patients undergoing ADT, and as a consequence of this having high serum levels of FSH, also had higher PSA levels [9,26]. In contrast, FSH did not show significant effect on PSA induction in LNCaP cells. The difference in response to FSH in these 2 cell lines is likely due to the fact that LNCaP cells are not under selec-tion pressure of the androgen-depleted environment , whereas C4-2 cells are not depending on androgens to proliferate although they induce AR and PSA upon treat-ment with androgens.
Unlike the gonads, where cAMP is the main second messenger of FSH action, the major signaling cascade activated by FSHR in CaP cells is PI3K/Akt. FSH has been reported to utilize the PI3K/Akt signaling pathway in the progression and migration of many cancers includ-ing breast cancer [15,20−22]. In the present study, we showed that FSH augmented levels of p-Akt and also increased b-catenin levels in both C4-2 and PC-3 cells. It is tempting to speculate that reduced androgen action is compensated through signal transduction pathways shared with FSH, as recently demonstrated in the testis tissue .
In the majority of studies investigating PC-3 cells, the AR is not detected. However, some studies have stated that the AR is only detectable after DHT treatment . We found that very high concentration FSH was able to induce
AR expression in PC-3 cells and the expression was corre-lated with significant cell proliferation. This finding may corroborate the role of AR, as in the presence of FSH, these cells did not require androgens to proliferate. This finding may also explain the absence of AR detection in some stud-ies. We speculate that FSH can act as a substitute for andro-gens though activation of the mitogenic signals that may amplify the activity of the AR in a low-ligand environment, possibly mediated by targeting the transcriptional machin-ery or the AR itself, via genomic and nongenomic mecha-nisms. Further, we observed that enzalutamide abrogated FSH-stimulated induction of PSA and p-Akt in C4-2 cells and in parallel, a p-Akt inhibitor not only inhibited p-Akt, but also resulted in reduced PSA concentration. An impor-tant finding was that FSH also led to the increase of b-cate-nin, which is a downstream target of Akt and known to play a role in the proliferation and migration in CaP cells . These results together suggest a cross-talk between AR and FSHR signaling pathways, likely also affecting downstream targets.
During ADT of CaP patients with GnRH agonists, FSH levels drop initially and then gradually rebound toward pre-treatment levels [7,8]. This, and the evidence of the correla-tion between levels of FSH and CaP progression as well as the shorter time to the development of CRCaP [10,14] sug-gests that FSH/FSHR may play a pivotal role in this con-text. The potential mechanisms of how FSH influences the progression to CRCaP may include (1) activation of PI3K/ Akt a signaling shared by AR and FSH, (2) increased b-cat-enin, which has been reported to be a relatively specific coactivator of the AR, (3) expression of the c-Myc gene, related to tumor growth regardless of the AR, and (4) the FSH signaling pathway promoting the interaction between transcription factors and AR, and thereby by increasing the transactivation of the AR to initiate transcription of genes normally exclusively regulated by androgen as reflected by PSA expression (Fig. 6).
More studies are warranted in order to elucidate the sig-nificance of FSH action in the context of the progression of CaP.
Fig. 6. The potential mechanisms of how FSH influences the progression of androgen dependent prostate cancer (PC) to castration resistant PC (CRPC). ADT = Androgen deprivation therapy, FSH = follicle-stimulating hormone, FSHR = follicle-stimulating hormone receptor, LH = Luteinizing hormone.
Conflict of interest
The authors have no conflicts of interest to disclose.