The chemoresistance of prostate cancer (PCa) is invariably associated with the aggressiveness and metastasis of this disease. New emerging evidence indicates that the epithelial-to-mesenchymal transition (EMT) may play pivotal roles in the development of chemoresistance and metastasis. As a hallmark of EMT, E-cadherin is suggested to be a key marker in the development of chemoresistance. However, the molecular mechanisms underlying PCa chemoresistance remain unclear. The current study aimed to explore the association between EMT and chemoresistance in PCa as well as whether changing the expression of E-cadherin would affect PCa chemoresistance. Parental PC3 and DU145 cells and their chemoresistant PC3-TxR and DU145-TxR cells were analyzed. PC3-TxR and DU145-TxR cells were transfected with E-cadherin-expressing lentivirus to overexpress E-cadherin; PC3 and DU145 cells were transfected with small interfering RNA to silence E-cadherin. Changes of EMT phenotype-related markers and signaling pathways were assessed by Western blotting and quantitative real-time polymerase chain reaction. Tumor cell migration, invasion, and colony formation were then evaluated by wound healing, transwell, and colony formation assays, respectively. The drug sensitivity was evaluated using MTS assay. Chemoresistant PC3-TxR and DU145-TxR cells exhibited an invasive and metastatic phenotype that associated with EMT, including the down-regulation of E-cadherin and up-regulation of Vimentin, Snail, and N-cadherin, comparing with that of parental PC3 and DU145 cells. When E-cadherin was overexpressed in PC3-TxR and DU145-TxR cells, the expression of Vimentin and Claudin-1 was down-regulated, and tumor cell migration and invasion were inhibited. In particular, the sensitivity to paclitaxel was reactivated in E-cadherin-overexpressing PC3-TxR and DU145-TxR cells. When E-cadherin expression was silenced in parental PC3 and DU145 cells, the expression of Vimentin and Snail was up-regulated, and, particularly, the sensitivity to paclitaxel was decreased. Interestingly, Notch-1 expression was up-regulated in PC3-TxR and DU145-TxR cells, whereas the E-cadherin expression was down-regulated in these cells comparing with their parental cells. The use of γ-secretase inhibitor, a Notch signaling pathway inhibitor, significantly increased the sensitivity of chemoresistant cells to paclitaxel. The down-regulation of E-cadherin enhances PCa chemoresistance via Notch signaling, and inhibiting the Notch signaling pathway may reverse PCa chemoresistance.

With changes in lifestyle and dietary patterns, the incidence of prostate cancer in China has been increasing steadily, and it has become one of the most common malignancies in men. Chemotherapy remains a primary treatment for prostate cancer, but the subsequent development of drug resistance by tumor cells markedly compromises its therapeutic efficacy. Growth differentiation factor 15 (GDF15) has been shown to be closely associated with tumor cell proliferation and metastasis; however, its contribution to the drug resistance of prostate cancer cells within the tumor microenvironment has not been systematically investigated. In this study, we treated drug-resistant prostate cancer cells (PC3-TXR and DU145-TXR) with conditioned medium (CM) and examined GDF15 expression by Western blotting, real-time PCR, and ELISA. We then exposed drug-resistant cells to various concentrations of recombinant GDF15 (rGDF15) and CM, and assessed invasive and metastatic abilities as well as sensitivity to paclitaxel using Transwell and CCK-8 assays. We generated GDF15-knockout osteocytes using CRISPR-Cas9 technology and detected the expression of resistance-related signaling pathway components and epithelial–mesenchymal transition (EMT) markers. These findings were further validated through subcutaneous tumor formation assays in mice combined with immunohistochemistry to explore the mechanism by which GDF15 regulates drug resistance and metastasis in the crosstalk between drug-resistant prostate cancer cells and bone cells. Our results revealed that GDF15 expression was significantly upregulated in both drug-resistant prostate cancer cells and their surrounding microenvironment. rGDF15 enhanced the invasion and drug resistance of resistant cells, whereas knockout of GDF15 effectively inhibited these effects. Furthermore, we demonstrated that GDF15 regulates the biological behavior of drug-resistant cells by targeting and modulating the AKT signaling pathway and by promoting EMT initiation and progression. These findings clarify the molecular pathway through which GDF15 governs drug resistance in prostate cancer cells, offering a new direction for the treatment of tumor metastasis and biologically targeted therapy.