Abstract
Cyclin‐dependent kinase 7 (CDK7) is a protein kinase that plays a major role in transcription initiation. Yes‐associated protein (YAP) is a main effector of the Hippo/YAP signalling pathway. Here, we investigated the role of CDK7 on YAP regulation in human malignant pleural mesothelioma (MPM). We found that in microarray samples of human MPM tissue, immunohistochemistry staining showed correlation between the expression level of CDK7 and YAP (n = 70, r = .513). In MPM cells, CDK7 expression level was significantly correlated with GTIIC reporter activity (r = .886, P = .019). Inhibition of CDK7 by siRNA decreased the YAP protein level and the GTIIC reporter activity in the MPM cell lines 211H, H290 and H2052. Degradation of the YAP protein was accelerated after CDK7 knockdown in 211H, H290 and H2052 cells. Inhibition of CDK7 reduced tumour cell migration and invasion, as well as tumorsphere formation ability. Restoration of the CDK7 gene rescued the YAP protein level and GTIIC reporter activity after siRNA knockdown in 211H and H2052 cells. Finally, we performed a co‐immunoprecipitation analysis using an anti‐YAP antibody and captured the CDK7 protein in 211H cells. Our results suggest that CDK7 inhibition reduces the YAP protein level by promoting its degradation and suppresses the migration and invasion of MPM cells. Cyclin‐dependent kinase 7 may be a promising therapeutic target for MPM.
Highlights
Malignant pleural mesothelioma (MPM) is highly invasive and has a poor prognosis
Our IHC results implied that there may be some relationship between Yes-associated protein (YAP) and Cyclin-dependent kinase 7 (CDK7), which we further investigated in six MPM cell lines (211H, H290, H2452, H2052, MS-1 and H28) and one normal mesothelial cell line (LP-9)
To confirm that the decreased YAP expression was caused by CDK7 inhibition, we evaluated the YAP expression level under forced CDK7 restoration in 211H and H2052 cells treated with CDK7 3′UTR siRNA
Summary
Malignant pleural mesothelioma (MPM) is highly invasive and has a poor prognosis. The pathogenesis of MPM is mainly related to asbestos exposure, but genetic susceptibility is receiving increased attention.[1,2,3] Overall, the current recommended treatment is a combination of surgery, radiation therapy, chemotherapy and immunotherapy, but median overall survival remains only approximately 7 months.[4,5] Novel therapeutic targets for patients with MPM are needed.Yes-associated protein (YAP), a transcriptional coactivator, is the major regulatory effector in the Hippo pathway, and its overexpression contributes to the development of many cancers and resistance to anticancer drugs.[6,7,8] at present, YAP is a new anticancer research hotspot. 3.2 | CDK7 expression level is consistent with activity of the Hippo pathway (YAP) in MPM cell lines The Western blot results showed that the protein expression level of CDK7 in 211H, H290, H2052 and MS-1 cells was higher than in H2452 and H28 cells (Figure 2A,B).
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