Heat shock protein 70 inhibitors suppress androgen receptor expression in LNCaP95 prostate cancer cells

Abstract

Androgen deprivation therapy is initially effective for treating patients with advanced prostate cancer; however, the prostate cancer gradually becomes resistant to androgen deprivation therapy, which is termed castration‐resistant prostate cancer (CRPC). Androgen receptor splice variant 7 (AR‐V7), one of the causes of CRPC, is correlated with resistance to a new‐generation AR antagonist (enzalutamide) and poor prognosis. Heat shock protein 70 (Hsp70) inhibitor is known to decrease the levels of full‐length AR (AR‐FL), but little is known about its effects against CRPC cells expressing AR‐V7. In this study, we investigated the effect of the Hsp70 inhibitors quercetin and VER155008 in the prostate cancer cell line LNCaP95 that expresses AR‐V7, and explored the mechanism by which Hsp70 regulates AR‐FL and AR‐V7 expression. Quercetin and VER155008 decreased cell proliferation, increased the proportion of apoptotic cells, and decreased the protein levels of AR‐FL and AR‐V7. Furthermore, VER155008 decreased AR‐FL and AR‐V7 mRNA levels. Immunoprecipitation with Hsp70 antibody and mass spectrometry identified Y‐box binding protein 1 (YB‐1) as one of the molecules regulating AR‐FL and AR‐V7 at the transcription level through interaction with Hsp70. VER155008 decreased the phosphorylation of YB‐1 and its localization in the nucleus, indicating that the involvement of Hsp70 in AR regulation might be mediated through the activation and nuclear translocation of YB‐1. Collectively, these results suggest that Hsp70 inhibitors have potential anti‐tumor activity against CRPC by decreasing AR‐FL and AR‐V7 expression through YB‐1 suppression.

The heat shock protein 70 inhibitor VER155008 suppresses the expression of HSP27, HOP and HSP90β and the androgen receptor, induces apoptosis, and attenuates prostate cancer cell growth

“…30,31 In LNCaP cells, VER incubation led to a significant activation of caspases over the entire incubation period of 72 hours, as previously shown in lung cancer and melanoma cells. AR, androgen receptor; DMSO, dimethyl sulfoxide; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; PSA, prostate specific antigen; qRT-PCR, real-time quantitative reverse transcription polymerase chain reaction; SD, standard deviation; VER, VER155008 *P < 0.05 nuclear translocation, this might be another explanation besides a potential YB-1-AR interaction described by Kita et al 29 in PCa. This is in line with the description of VER to induce apoptosis in both a caspase-3/7-dependent and -independent manner in different tumors.…”

Hsp70 and gama-Semino protein as possible prognostic marker of prostate cancer

“…To help with accuracy, researchers have suggested using the ratio between free to total gama-SM protein level (87). Additionally, studies have shown that Hsp70 can also be used as a co-biomarker for PCa with gama-SM (2, 56, 83). Studies have demonstrated that although Hsp70 has relatively the same level of accuracy of gama-SM in the diagnostics of PCa, it had a far higher level of accuracy in identifying the prognostic and metastatic implications of PCa protein (42, 56).…”

“…Additionally, studies have shown that Hsp70 can also be used as a co-biomarker for PCa with gama-SM (2, 56, 83). Studies have demonstrated that although Hsp70 has relatively the same level of accuracy of gama-SM in the diagnostics of PCa, it had a far higher level of accuracy in identifying the prognostic and metastatic implications of PCa protein (42, 56). Furthermore, to consolidate, Hsp70 and gama-SM inhibitors have been shown to provide therapeutic relief to PCa cells (82, 83, 88).…”

“…In vitro anticancer chemotherapeutic prospects of cisplatin and pifithrin-u combined usage have been experimented in three PCa cell lines: LNCaP (androgen sensitive), PC-3, and DU-145 (androgen insensitive). All three cell lines were found to have comparable sensitivity to the combination therapy over a 72hr treatment (24, 42, 56, 57, 63). HT29 and HCT116 (a colon cancer cell line) had a similar sensitivity after being treated with pifithrin-u.…”

“…Researchers have found that AR signaling is highly associative with the regulation of the proliferation, apoptosis, and invasion of PCa, and it has been seen that the overexpression of AR signaling is one of the main causes of Castrate Resistant PCa (CRPCa) (57). Studies have found that by binding to the Y-box binding protein 1 (YB-1), Hsp70 inhibitors are able to control AR signaling in CRPCa cells (56), thus indicating a relationship between Hsp70 and AR signaling. Overall, by regulating these signaling pathways, Hsp70, along with its chaperoning ability, pertains the ability to aid with PCa tumor growth and proliferation.…”