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Transforming Growth Factor β Mediates Drug Resistance by Regulating the Expression of Pyruvate Dehydrogenase Kinase 4 in Colorectal Cancer.

ABSTRACT: Drug resistance is one of the main causes of colon cancer recurrence. However, our understanding of the underlying mechanisms and availability of therapeutic options remains limited. Here we show that expression of pyruvate dehydrogenase kinase 4 (PDK4) is positively correlated with drug resistance of colon cancer cells and induced by 5-fluorouracil (5-FU) treatment in drug-resistant but not drug-sensitive cells. Knockdown of PDK4 expression sensitizes colon cancer cells to 5-FU or oxaliplatin-induced apoptosis in vitro and increases the effectiveness of 5-FU in the inhibition of tumor growth in a mouse xenograft model in vivo In addition, we demonstrate for the first time that TGFβ mediates drug resistance by regulating PDK4 expression and that 5-FU induces PDK4 expression in a TGFβ signaling-dependent manner. Mechanistically, knockdown or inhibition of PDK4 significantly increases the inhibitory effect of 5-FU on expression of the anti-apoptotic factors Bcl-2 and survivin. Importantly, studies of patient samples indicate that expression of PDK4 and phosphorylation of Smad2, an indicator of TGFβ pathway activation, show a strong correlation and that both positively associate with chemoresistance in colorectal cancer. These findings indicate that the TGFβ/PDK4 signaling axis plays an important role in the response of colorectal cancer to chemotherapy. A major implication of our studies is that inhibition of PDK4 may have considerable therapeutic potential to overcome drug resistance in colorectal cancer patients, which warrants the development of PDK4-specific inhibitors.

SUBMITTER: Zhang Y

PROVIDER: S-EPMC5016137 | biostudies-other | 2016 Aug

REPOSITORIES: biostudies-other

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Project description:Lung cancer is the second most common cancer and the leading cause of cancer-related deaths. Despite recent advances in the development of targeted therapies, patients with advanced disease remain incurable, mostly because metastatic non-small cell lung carcinomas (NSCLC) eventually become resistant to tyrosine kinase inhibitors (TKIs). Kinase inhibitors have the potential for target promiscuity because the kinase super family is the largest family of druggable genes that binds to a common substrate (ATP). As a result, TKIs often developed for a specific purpose have been found to act on other targets. Drug affinity chromatography has been used to show that dasatinib interacts with the TGFβ type I receptor (TβR-I), a serine-threonine kinase. To determine the potential biological relevance of this association, we studied the combined effects of dasatinib and TGFβ on lung cancer cell lines. We found that dasatinib treatment alone had very little effect; however, when NSCLC cell lines were treated with a combination of TGFβ and dasatinib, apoptosis was induced. Combined TGFβ-1 + dasatinib treatment had no effect on the activity of Smad2 or other non-canonical TGFβ intracellular mediators. Interestingly, combined TGFβ and dasatinib treatment resulted in a transient increase in p-Smad3 (seen after 3 hours). In addition, when NSCLC cells were treated with this combination, the pro-apoptotic protein BIM was up-regulated. Knockdown of the expression of Smad3 using Smad3 siRNA also resulted in a decrease in BIM protein, suggesting that TGFβ-1 + dasatinib-induced apoptosis is mediated by Smad3 regulation of BIM. Dasatinib is only effective in killing EGFR mutant cells, which is shown in only 10% of NSCLCs. Therefore, the observation that wild-type EGFR lung cancers can be manipulated to render them sensitive to killing by dasatinib could have important implications for devising innovative and potentially more efficacious treatment strategies for this disease.

Project description:BACKGROUND:Adenomyosis is a medical condition defined by the abnormal presence of endometrial tissue within the myometrium, in which fibrosis occurs with new collagen deposition and myofibroblast differentiation. In this study, the effect of several mediators and growth factors on collagen expression was investigated on human endometrial stromal cells (fibroblasts) derived from adenomyotic endometrium. EXPERIMENTAL APPROACH:RT-PCR, Western blot analysis, pharmacological interventions and siRNA interference were applied to primary cultured human endometrial stromal cells (fibroblasts). Immunohistochemistry was used to analyze protein expression in adenomyotic endometrium tissue specimens. RESULTS:Of the tested mediators, transforming growth factor β1 (TGFβ1) and its isoforms were effective to induce collagen and connective tissue growth factor (CTGF) expression. Collagen and CTGF induction by TGFβ1 could be reduced by the inhibitors targeting DNA transcription, protein translation, and Smad2/3 signaling. Interestingly, TGFβ1 induced Smad2/3 phosphorylation and CTGF mRNA expression, but not collagen mRNA expression, suggesting that TGFβ1 mediates collagen expression through CTGF induction and Smad2/3 activation. In parallel, TGFβ1 and CTGF also induced expression of heat shock protein (HSP) 47, a protein required for the synthesis of several types of collagens. However, only CTGF siRNA knockdown, could compromise TGFβ1-induced collagen expression. Finally, the immunohistochemistry revealed vimentin- and α-SMA-positive staining for (myo)fibroblasts, TGFβ1, collagen, and CTGF in the subepithelial stroma region of human adenomyotic endometria. CONCLUSION AND IMPLICATIONS:We reveal here that TGFβ1, collagen, and CTGF are expressed in the stroma of adenomyotic endometria and demonstrate that TGFβ1 can induce collagen production in endometrium-derived fibroblasts through cellular Smad2/3-dependent signaling pathway and CTGF expression, suggesting that endometrial TGFβ may take part in the pathogenesis of adenomyosis and ectopic endometrium may participate in uterine adenomyosis.

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Transforming Growth Factor β Mediates Drug Resistance by Regulating the Expression of Pyruvate Dehydrogenase Kinase 4 in Colorectal Cancer.

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