Dynamic changes in the expression of estrogen receptors have been shown with the progression of prostate cancer. Studies have shown that in the early stages of prostatic carcinoma, the genes encoding the ESR1 and ESR2 estrogen receptors are silenced, occurring low expression of these receptors in tumors confined on prostate. However, ESR1 reappears with cancer progression and, in the metastasis site, the ESR2 is highly express, suggesting that the functions of inducer (attributed to the ESR1 ) and suppressor ( attributed ESR2 ) of the tumor need to be better investigated. The prostate cancer cell line PC-3 was isolated from bone metastasis of prostate cancer, and studies have shown that these cells are androgen independent and used as model of CRPC (castration-resistant prostate cancer). Study from our laboratory has shown the presence of ESR1 and ESR2 in these cells.In cancer, depending on the tissue and physiological context, the transcription factor Krüppel -like factor 4 (KLF4) has effects as a tumor suppressor or oncogene. Regarding the expression of KLF4 in prostate cancer, the literature is limited and controversial. Recent study from our laboratory has shown an increase of KLF4 level in PC-3 cells between 10 and 30 minutes of incubation with the ESR1 estrogen receptor agonist (PPT ), suggesting a role of estrogen in the regulation of the degradation of this transcription factor. In fact, a recent study has shown that estrogens can increase the expression of KLF4 and stimulate the proliferation of breast cancer cells by decreasing the expression of von Hippel- Lindau protein, VHL, which is involved in the turnover of KLF4. Furthermore, another study has shown that phosphorylation of the Ser123 KLF4 by ERK1/2 leads to the recruitment and binding of ²TrCP2 (component E3 ubiquitin ligase) to the N-terminal domain of the protein KLF4. The binding of ²TrCP results in ubiquitination and degradation of KLF4. In PC-3 cells, cellular localization of KLF4 and the mechanisms involved in the expression of this factor need be explored.Therefore, the aim of this study is to investigate the effects of activation of the classical estrogen receptor ESR1 and ESR2 in the cellular localization and regulation of the expression of the transcription factor KLF4 in androgen-independent prostate cancer cell PC-3. After the activation of ESR1 and ESR2 will be determined: i) the cellular localization of KLF4; ii) the stability of KLF4 in the presence of protein synthesis inhibitor cycloheximide and proteasome inhibitor MG132; and iii) the regulation of the expression of VHL and ²TrCP proteins by estrogen receptors.
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