Raf kinase inhibitor protein (RKIP) blocks signal transducer and activator of transcription 3 (STAT3) activation in breast and prostate cancer.

Raf kinase inhibitor protein (RKIP) is a member of the phosphatidylethanolamine-binding-protein (PEBP) family that modulates the action of many kinases involved in cellular growth, apoptosis, epithelial to mesenchymal transition, motility, invasion and metastasis. Previously, we described an inverse association between RKIP and signal transducers and activators of transcription 3 (STAT3) expression in gastric adenocarcinoma patients. In this study, we elucidated the mechanism by which RKIP regulates STAT3 activity in breast and prostate cancer cell lines. RKIP over expression inhibited c-Src auto-phosphorylation and activation, as well as IL-6-, JAK1 and 2-, and activated Raf-mediated STAT3 tyrosine and serine phosphorylation and subsequent activation. In MDA-231 breast cancer cells that stably over express RKIP, IL-6 treatment blocked STAT3 phosphorylation and transcriptional activation. Conversely, in RKIP knockdown MDA-231 cells: STAT3 phosphorylation and activation increased in comparison to parental MDA-231 cells. RKIP over expression resulted in constitutive physical interaction with STAT3 and blocked c-Src and STAT3 association. The treatment of DU145 prostate, but not PC3 prostate or MDA-231 breast, cancer cell lines with ENMD-1198 or MKC-1 dramatically increased expression of RKIP. Overexpression of RKIP sensitized PC3 and MDA-231 cells to MTI-induced apoptosis. Moreover, MTI treatment resulted in a decrease in Src-mediated STAT3 tyrosine phosphorylation and activation, an effect that was significantly enhanced by RKIP over expression. In stable RKIP over expressing MDA-231 cells, tumor xenograft growth induced by activated STAT3 is inhibited. RKIP synergizes with MTIs to induce apoptosis and inhibit STAT3 activation of breast and prostate cancer cells. RKIP plays a critical role in opposing the effects of pro-oncogenic STAT3 activation.

Role of Raf kinase inhibitor protein in Helicobacter pylori-mediated signaling in gastric cancer.

Helicobacter pylori is a helical bacterium that colonizes the stomach in over half of the world's population. Infection with this bacterium has been linked to peptic ulcer disease and gastric cancer. The bacterium has been shown to affect regulatory pathways in its host cells through specific virulence factors that control gene expression. Infection with H. pylori increases levels of phosphorylation of Raf kinase inhibitor protein (pRKIP) in gastric adenocarcinoma (AGS) cells in vitro and in vivo. We investigated the role of H. pylori in the phosphorylation of RKIP as a possible mechanism to downregulate pro-survival signals in gastric adenocarcinoma. pRKIP induces RKIP transcriptional activity, which serves to induce apoptosis of damaged cells to prevent further tumorigenesis. Infection of wild type and RKIP knockout mice with H. pylori for 2 months further confirmed roles of RKIP and pRKIP in the prevention of gastric cancer progression. Loss of RKIP in AGS cells results in increased expression of the Cag A virulence factor after H. pylori infection and RKIP overexpression inhibits H. pylori-mediated STAT3 phosphorylation and STAT3 and NF-κB transcriptional activity. We examined the role of mTOR (mammalian target of rapamycin) after H. pylori infection on the phosphorylation of RKIP. Cells treated with rapamycin, an inhibitor of mTOR, displayed less expression of pRKIP after H. pylori infection. Microarray antibody analysis was conducted on wild-type and RKIP-knockdown AGS cells and showed that in the absence of RKIP, there was increased expression of pro-tumorigenic proteins such as EGFR, Raf-1, and MAPKs. Although further work is needed to confirm the interaction of RKIP and mTOR in AGS cells as a result of H. pylori infection, we hypothesize that H. pylori-mediated induction of pro-survival signaling in gastric epithelial cells induces a feedback response through the activation of RKIP. The phosphorylated, or active, form of RKIP is important in protecting gastric epithelial cells from tumorigenesis after H. pylori infection.

Reversal of chemosensitivity and induction of cell malignancy of a non-malignant prostate cancer cell line upon extracellular vesicle exposure.

BACKGROUND: Extracellular vesicle (EV) trafficking is a fundamental cellular process that occurs in cells and is required for different aspects of pathophysiology. EV trafficking leads to changes in cellular function including apoptosis, angiogenesis and proliferation required for increased tumor formation. RESULTS: We report several phenotypic changes mediated by EVs isolated from non-malignant and malignant prostate cells as well as patient biopsied prostate tumor samples. EVs can reverse the resistance of prostate cancer cells to camptothecin EVs isolated from non-malignant PrECs (Prostate Epithelial Cells) can reverse soft agar colony formation of malignant DU145 cells, with the reciprocal effect observed. Isolation of EVs from 2 Gleason grade 8 prostate cancer patients significantly induced soft agar colony formation of non-malignant PrECs. We have identified proteins via antibody and Mass spectrometry analysis that may be responsible for the phenotypic changes. Mass spectrometry analysis of protein lysates using ProteoIQ revealed protein candidates associated with gene ontology annotations that may be responsible for this phenotypic change. Ingenuity Pathway Analysis was used to identify statistically relevant canonical pathways and functions associated the protein IDs and expression values obtained using ProteoIQ. Western blot analysis confirmed the increase of 14-3-3 zeta, pRKIP and prohibitin protein levels in PrEC cells co-cultured with patient EVs. 14-3-3 proteins were also found as common proteins of 3 other Gleason grade 8 patients. CONCLUSION: Our study provides a rational basis to further investigate putative proteins, such as 14-3-3 and prohibitin and genetic factors that may be responsible for phenotypic changes that are associated with prostate cancer progression.

RKIP phosphorylation and STAT3 activation is inhibited by oxaliplatin and camptothecin and are associated with poor prognosis in stage II colon cancer patients.

BACKGROUND: A major obstacle in treating colorectal cancer (CRC) is the acquired resistance to chemotherapeutic agents. An important protein in the regulation of cancer cell death and clinical outcome is Raf kinase inhibitor protein (RKIP). In contrast, activated signal transducer and activator of transcription 3 (STAT3) is a protein that promotes tumor cell survival by inhibiting apoptosis and has an important role in cancer progression in many of cancer types. The aim of this study was to evaluate the regulation of RKIP and STAT3 after treatment with clinically relevant chemotherapeutic agents (camptothecin (CPT) and oxaliplatin (OXP)) and the cytokine interleukin-6 (IL-6) in HCT116 colon cancer cells as well as evaluate the association between RKIP and STAT3 with clinical outcome of Stage II colon cancer patients. METHODS: HCT-116 colon cancer cells were treated with CPT, OXP, and IL-6 separately or in combination in a time and dose-dependent manner and examined for phosphorylated and non-phosphorylated RKIP and STAT3 via Western blot analysis. STAT3 transcriptional activity was measured via a luciferase reporter assay in HCT116 cells treated with CPT, IL-6 or transfected with JAK 1, 2 separately or in combination. We extended these observations and determined STAT3 and RKIP/ pRKIP in tumor microarrays (TMA) in stage II colon cancer patients. RESULTS: We demonstrate IL-6-mediated activation of STAT3 occurs in conjunction with the phosphorylation of RKIP in vitro in human colon cancer cells. OXP and CPT block IL-6 mediated STAT3 activation and RKIP phosphorylation via the inhibition of the interaction of STAT3 with gp130. We determined that STAT3 and nuclear pRKIP are significantly associated with poor patient prognosis in stage II colon cancer patients. CONCLUSIONS: In the analysis of tumor samples from stage II colon cancer patients and the human colon carcinoma cell line HCT116, pRKIP and STAT3, 2 proteins potentially involved in the resistance to conventional treatments were detected. The phosphorylation of pRKIP and STAT3 are induced by the cytokine IL-6 and suppressed by the chemotherapeutic drugs CPT and OXP. Therefore, these results suggest that STAT3 and pRKIP may serve as prognostic biomarkers in stage II colon cancer patients and may improve chemotherapy.

Regulation of RKIP function by Helicobacter pylori in gastric cancer.

Helicobacter pylori (H. pylori) is a gram-negative, spiral-shaped bacterium that infects more than half of the world's population and is a major cause of gastric adenocarcinoma. The mechanisms that link H. pylori infection to gastric carcinogenesis are not well understood. In the present study, we report that the Raf-kinase inhibitor protein (RKIP) has a role in the induction of apoptosis by H. pylori in gastric epithelial cells. Western blot and luciferase transcription reporter assays demonstrate that the pathogenicity island of H. pylori rapidly phosphorylates RKIP, which then localizes to the nucleus where it activates its own transcription and induces apoptosis. Forced overexpression of RKIP enhances apoptosis in H. pylori-infected cells, whereas RKIP RNA inhibition suppresses the induction of apoptosis by H. pylori infection. While inducing the phosphorylation of RKIP, H. pylori simultaneously targets non-phosphorylated RKIP for proteasome-mediated degradation. The increase in RKIP transcription and phosphorylation is abrogated by mutating RKIP serine 153 to valine, demonstrating that regulation of RKIP activity by H. pylori is dependent upon RKIP's S153 residue. In addition, H. pylori infection increases the expression of Snail, a transcriptional repressor of RKIP. Our results suggest that H. pylori utilizes a tumor suppressor protein, RKIP, to promote apoptosis in gastric cancer cells.