Caveolin-1, a metastasis-related gene that promotes cell survival in prostate cancer

Metastasis represents the ultimate target in cancer therapy as this complex biological process is the direct cause of mortality for a variety of human malignancies. The current high level of mortality from prostate cancer results in large part from the inexorable growth of overt or occult metastasis present at the time of diagnosis. Currently, there are no curative therapies for metastatic prostate cancer. To better understand the metastatic phenotype in prostate cancer, we developed a strategy to identify mRNAs that are expressed differentially in cell lines derived from primary versus metastatic mouse prostate cancer using differential display-PCR. In using this system a number of metastasis-related sequences were identified including a cDNA that encodes caveolin-1. Caveolin-1 was found to be overexpressed not only in metastatic mouse prostate cancer, but also in human metastatic disease. Recent studies have indicated that suppression of caveolin-1 expression induces androgen sensitivity in high caveolin-1, androgen-insensitive mouse prostate cancer cells derived from metastases. Conversely, overexpression of caveolin-1 leads to androgen insensitivity in low caveolin, androgen-sensitive mouse prostate cancer cells. Caveolin-1, therefore, is both a metastasis-related gene as well as a candidate androgen resistance gene for prostate cancer in man. Interestingly, recent studies also point to a potential role for caveolin-1 in the resistance of various malignancies to multiple antineoplastic agents. The linkage of caveolin-1 expression with the androgen-resistant phenotype in prostate cancer and the multidrug resistance phenotype in various solid tumors establishes a novel paradigm for understanding these clinically important and now potentially related processes in malignant progression.     

SPRY4-IT1 promotes survival of colorectal cancer cells through regulating PDK1-mediated glycolysis

ABSTRACT

Colorectal cancer (CRC) becomes the third leading cause of cancer-related deaths worldwide recently. The prognosis of CRC is still poor in decades, and targeted therapy is still a potential effective treatment. Long non-coding RNAs (lncRNAs) could regulate series of cellular functions and developmental processes. LncRNA-SPRY4-IT1 (GenBank ID AK024556) is derived from an intron of the SPRY4 gene, which was highly expressed in melanoma cells and affected the progression of multiple types of cancers. However, the mechanism of SPRY4-IT1 in CRC progression remains unclear. Herein, we found the high level of SPRY4-IT1 in human colorectal cancer (CRC) tissues and cells, and correlated with patients’ prognosis. We further noticed that SPRY4-IT1 regulated CRC cell growth and glycolysis, and promoting PDK1 expression. Our data further confirmed that SPRY4-IT1 regulated CRC progression targeting PDK1. We therefore thought SPRY4-IT1 could serve as a promising molecular target for the treatment of CRC.     

Apoptosis evasion: the role of survival pathways in prostate cancer progression and therapeutic resistance

The ability of a tumor cell population to grow exponentially represents an imbalance between cellular proliferation and cellular attrition. There is an overwhelming body of evidence suggesting the ability of tumor cells to avoid programmed cellular attrition, or apoptosis, is a major molecular force driving the progression of human tumors. Apoptotic evasion represents one of the true hallmarks of cancer and appears to be a vital component in the immunogenic, chemotherapeutic, and radiotherapeutic resistance that characterizes the most aggressive of human cancers [Hanahan and Weinberg, 2000]. The challenges in the development of effective treatment modalities for advanced prostate cancer represent a classic paradigm of the functional significance of anti-apoptotic pathways in the development of therapeutic resistance.     

Clusterin enhances AKT2-mediated motility of normal and cancer prostate cells through a PTEN and PHLPP1 circuit

Clusterin (CLU) is a chaperone-like protein with multiple functions. sCLU is frequently upregulated in prostate tumor cells after chemo- or radiotherapy and after surgical or pharmacological castration. Moreover, CLU has been documented to modulate the cellular homolog of murine thymoma virus akt8 oncogene (AKT) activity. Here, we investigated how CLU overexpression influences phosphatidylinositol 3′-kinase (PI3K)/AKT signaling in human normal and cancer epithelial prostate cells. Human prostate cells stably transfected with CLU were broadly profiled by reverse phase protein array (RPPA), with particular emphasis on the PI3K/AKT pathway. The effect of CLU overexpression on normal and cancer cell motility was also tested. Our results clearly indicate that CLU overexpression enhances phosphorylation of AKT restricted to isoform 2. Mechanistically, this can be explained by the finding that the phosphatase PH domain leucine-rich repeat-containing protein phosphatase 1 (PHLPP1), known to dephosphorylate AKT2 at S474, is markedly downregulated by CLU, whereas miR-190, a negative regulator of PHLPP1, is upregulated. Moreover, we found that phosphatase and tensin homolog (PTEN) was heavily phosphorylated at the inhibitory site S380, contributing to the hyperactivation of AKT signaling. By keeping AKT2 phosphorylation high, CLU dramatically enhances the migratory behavior of prostate epithelial cell lines with different migratory and invasive phenotypes, namely prostate normal epithelial 1A (PNT1A) and prostatic carcinoma 3 (PC3) cells. Altogether, our results unravel for the first time a circuit by which CLU can switch a low migration phenotype toward a high migration phenotype, through miR-190-dependent downmodulation of PHLPP1 expression and, in turn, stabilization of AKT2 phosphorylation.     

Pretreatment of docetaxel enhances TRAIL-mediated apoptosis in prostate cancer cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising cancer therapeutic agent because of its tumor selectivity. TRAIL is known to induce apoptosis in cancer cells but spare most normal cells. In this study, we examined whether treatment of docetaxel (DTX) can enhance apoptotic cell death by TRAIL against androgen-independent prostate cancer (AIPC). The cell death effect of combinations of TRAIL and docetaxel on prostate cancer cell lines (androgen-dependent LNCaP and its derived androgen-independent, metastatic C4-2B) was evaluated by synergisms of apoptosis. Western blot assay and DNA fragmentation assay were used to study the underlying mechanisms of cell death and search for any mechanisms of enhancement of TRAIL induced apoptosis in the presence of docetaxel. In addition, we investigated the in vitro anti-tumor effects of combined docetaxel and TRAIL using MAP kinase inhibitors. Docetaxel itself could not induce apoptotic cell death in 24 h even in high concentration. Apoptotic cell death, however, was drastically enhanced by pretreatment of docetaxel 20 h before TRAIL treatment. Docetaxel enhanced the PARP-1 cleavage and caspases activation by TRAIL especially in androgen-independent, metastatic C4-2B cell line, mainly by phosphorylation of Bcl-2 by JNK activation. It appears that apoptotic cell death was protected by the JNK inhibitor SP600125. The results of our study show that pretreatment of docetaxel is able to enhance the apoptosis produced by TRAIL in prostate cancer cells, especially in hormone-refractory prostate cancer (HRPC).     

WWOX suppresses prostate cancer cell progression through cyclin D1-mediated cell cycle arrest in the G1 phase

WW domain-containing oxidoreductase (WWOX) has been reported to be a tumor suppressor in multiple cancers, including prostate cancer. WWOX can induce apoptotic responses to inhibit tumor progression, and the other mechanisms of WWOX in tumor suppression have also been reported recently. In this study, we found significant down-regulation of WWOX in prostate cancer specimens and prostate cancer cell lines compared with the normal controls. In addition, an ectopically increased WWOX expression repressed tumor progression both in vitro and in vivo. Interestingly, overexpression of WWOX in 22Rv1 cells led to cell cycle arrest in the G1 phase but did not affect sub-G1 in flow cytometry. GFP-WWOX overexpressed 22Rv1 cells were shown to inhibit cell cycle progression into mitosis under nocodazole treatment in flow cytometry, immunoblotting and GFP fluorescence. Further, cyclin D1 but not apoptosis correlated genes were down-regulated by WWOX both in vitro and in vivo. Restoration of cyclin D1 in the WWOX-overexpressed 22Rv1 cells could abolish the WWOX-mediated tumor repression. In addition, WWOX impair c-Jun-mediated cyclin D1 promoter activity. These results suggest that WWOX inhibits prostate cancer progression through negatively regulating cyclin D1 in cell cycle lead to G1 arrest. In summary, our data reveal a novel mechanism of WWOX in tumor suppression.     

WWOX suppresses prostate cancer cell progression through cyclin D1-mediated cell cycle arrest in the G1 phase

WW domain-containing oxidoreductase (WWOX) has been reported to be a tumor suppressor in multiple cancers, including prostate cancer. WWOX can induce apoptotic responses to inhibit tumor progression, and the other mechanisms of WWOX in tumor suppression have also been reported recently. In this study, we found significant down-regulation of WWOX in prostate cancer specimens and prostate cancer cell lines compared with the normal controls. In addition, an ectopically increased WWOX expression repressed tumor progression both in vitro and in vivo. Interestingly, overexpression of WWOX in 22Rv1 cells led to cell cycle arrest in the G1 phase but did not affect sub-G1 in flow cytometry. GFP-WWOX overexpressed 22Rv1 cells were shown to inhibit cell cycle progression into mitosis under nocodazole treatment in flow cytometry, immunoblotting and GFP fluorescence. Further, cyclin D1 but not apoptosis correlated genes were down-regulated by WWOX both in vitro and in vivo. Restoration of cyclin D1 in the WWOX-overexpressed 22Rv1 cells could abolish the WWOX-mediated tumor repression. In addition, WWOX impair c-Jun-mediated cyclin D1 promoter activity. These results suggest that WWOX inhibits prostate cancer progression through negatively regulating cyclin D1 in cell cycle lead to G1 arrest. In summary, our data reveal a novel mechanism of WWOX in tumor suppression.     

MiRNA-296-3p-ICAM-1 axis promotes metastasis of prostate cancer by possible enhancing survival of natural killer cell-resistant circulating tumour cells

Natural killer (NK) cells are important in host to eliminate circulating tumour cells (CTCs) in turn preventing the development of tumour cells into metastasis but the mechanisms are very poorly defined. Here we find that the expression level of miR-296-3p is much lower in the non-metastatic human prostate cancer (PCa) cell line P69 than that in the highly metastatic cell line M12, which is derived from P69. We demonstrate that miR-296-3p directly targets and inhibits the expression of intercellular adhesion molecule 1 (ICAM-1) in the malignant M12. The data from clinical tissue microarrays also show that miR-296-3p is frequently upregulated and ICAM-1 is reversely downregulated in PCa. Interestingly, ectopic expression of miR-296-3p in P69 increases the tolerance to NK cells whereas knockdown of miR-296-3p in M12 reduces the resistance to NK cells, which both phenotypes can be rescued by re-expression or silencing of ICAM-1 in P69 and M12, respectively. These results are also manifested in vivo by the decrease in the incidence of pulmonary tumour metastasis exhibited by knockdown of miR-296-3p in M12 when injected into athymic nude mice via tail vein, and consistently down-expression of ICAM-1 reverses this to increase extravasation of CTCs into lungs. Above results suggest that this newly identified miR-296-3p-ICAM-1 axis has a pivotal role in mediating PCa metastasis by possible enhancing survival of NK cell-resistant CTC. Our findings provide novel potential targets for PCa therapy and prognosis.     

Apolipoprotein C1 promotes prostate cancer cell proliferation in vitro

Here, we aimed to investigate the carcinogenic effects of apolipoprotein C1 (APOC1) in prostate cancer (PCa). APOC1 expression was evaluated in PCa and normal prostate specimens, and lentivirus‐mediated RNA interference was used to knockdown APOC1 in DU145 cells. The effects of APOC1 silencing on cell proliferation, cell cycle arrest, and apoptosis were assessed. APOC1 expression was much higher in PCa tissues than in normal tissues. Moreover, APOC1 silencing inhibited cell proliferation and colony formation, arrested cell cycle progression, and enhanced apoptosis in DU145 cells. Additionally, APOC1 silencing decreased survivin, phospho‐Rb, and p21 levels and increased cleaved caspase‐3 expression. These data supported the procarcinogenic effects of APOC1 in the pathogenesis of PCa and suggested that targeting APOC1 may have applications in the treatment of PCa.     

Calpain activation through galectin-3 inhibition sensitizes prostate cancer cells to cisplatin treatment

Prostate cancer will develop chemoresistance following a period of chemotherapy. This is due, in part, to the acquisition of antiapoptotic properties by the cancer cells and, therefore, development of novel strategies for treatment is of critical need. Here, we attempt to clarify the role of the antiapoptotic molecule galectin-3 in prostate cancer cells using siRNA and antagonist approaches. The data showed that Gal-3 inhibition by siRNA or its antagonist GCS-100/modified citrus pectin (MCP) increased cisplatin-induced apoptosis of PC3 cells. Recent studies have indicated that cisplatin-induced apoptosis may be mediated by calpain, a calcium-dependent protease, as its activation leads to cleavage of androgen receptor into an androgen-independent isoform in prostate cancer cells. Thus, we examined whether calpain activation is associated with the Gal-3 function of regulating apoptosis. Here, we report that Gal-3 inhibition by siRNA or GCS-100/MCP enhances calpain activation, whereas Gal-3 overexpression inhibits it. Inhibition of calpain using its inhibitor and/or siRNA attenuated the proapoptotic effect of Gal-3 inhibition, suggesting that calpain activation may be a novel mechanism for the proapoptotic effect of Gal-3 inhibition. Thus, a paradigm shift for treating prostate cancer is suggested whereby a combination of a non-toxic anti-Gal-3 drug together with a toxic chemotherapeutic agent could serve as a novel therapeutic modality for chemoresistant prostate cancers.     

Inhibition of cell survival signal protein kinase B/Akt by curcumin in human prostate cancer cells

Although curcumin has been shown to inhibit prostate tumor growth in animal models, its mechanism of action is not clear. To better understand the anti-cancer effects of curcumin, we investigated the effects of curcumin on cell survival factor Akt in human prostate cancer cell lines, LNCaP, PC-3, and DU-145. Our results demonstrated differential activation of Akt. Akt was constitutively activated in LNCaP and PC-3 cells. Curcumin inhibited completely Akt activation in both LNCaP and PC-3 cells. The presence of 10% serum decreased the inhibitory effect of curcumin in PC-3 cells whereas complete inhibition was observed in 0.5% serum. Very little or no activation of Akt was observed in serum starved DU-145 cells (0.5% serum). The presence of 10% serum activated Akt in DU-145 cells and was not inhibited by curcumin. Results suggest that one of the mechanisms of curcumin inhibition of prostate cancer may be via inhibition of Akt. To our knowledge this is the first report on the curcumin inhibition of Akt activation in LNCaP and PC-3 but not in DU-145 cells.     

Ectopic expression of CC chemokine receptor 7 promotes prostate cancer cells metastasis via Notch1 signaling

There currently exists no satisfactory treatment for patients with prostate cancer with local evolution and distant metastasis. Previous studies have confirmed the importance of CC chemokine receptor 7 (CCR7) in the invasion and metastasis of prostate cancer. And increasing evidence prove that Notch1 can play diametrically opposite roles in the development and progression of different tumors. To demonstrate the correlation between CCR7 and Notch1, PC-3 cells were transfected with pcDNA3.1-CCR7 or CCR7 si-RNA, respectively. Then Western blot analysis was used to detect the expressions of Notch1, ERK, P38, JNK, NF-κB, MMP-9, and epithelial-mesenchymal transition (EMT)-related proteins. Moreover, matrigel invasion assays were performed to assess the migratory and invasive activities of PC-3 cells. PcDNA3.1-CCR7 increased the expression of Notch1, phospho-MAPK, phospho-P65, MMP-9, N-cadherin, and Snail in PC-3 cells, but decreased the expression of E-cadherin. PcDNA3.1-CCR7 also promoted the migration and invasion of PC-3 cells. However, CCR7 si-RNA reversed the effect of pcDNA3.1-CCR7 in PC-3 cells. And MAPK and NF-κB pathway inhibitors were used to testify that activation of Notch1 induces EMT through MAPK and NF-κB pathway. All these results indicate that upregulation of Notch1 by CCR7 can accelerate the evolution of EMT and develop the invasion and metastasis in prostate cancer cells by activating MAPK and NF-κB signaling pathways in prostate cancer cells, which provides a new molecular evidence for targeted therapy in metastatic prostate cancer.     

Stromal-induced downregulation of miR-1247 promotes prostate cancer malignancy

Cancer progression is strictly dependent on the relationship between tumor cells and the surrounding stroma, which supports cancer malignancy promoting several crucial steps of tumor progression, including the execution of the epithelial to mesenchymal transition (EMT) associated with enhancement in cell invasion, resistance to both anoikis and chemotherapeutic treatments. Recently it has been highlighted the central role of microRNAs (miRNAs) as regulators of tumor progression. Notably, in several tumors a strong deregulation of miRNAs is observed, supporting proliferation, invasion, and metabolic reprogramming of tumor cells. Here we demonstrated that cancer-associated fibroblasts induce a downregulation of miR-1247 in prostate cancer (PCa) cells. We proved that miR-1247 repression is functional for the achievement of EMT and increased cell invasion as well as stemness traits. These phenomena contribute to promote the metastatic potential of PCa cells as demonstrated by increased lung colonization in in vivo experiments. Moreover, as a consequence of miR-1247 downregulation, we observed a correlated increased expression level of neuropilin-1, a miR-1247 target involved as a coreceptor in the epidermal growth factor receptor signaling. Taken together, our data highlight miR-1247 as a potential target for molecular therapies aimed to block the progression and diffusion of PCa.