No abstract

To better define malignant pleural mesothelioma (MPM) heterogeneity and identify molecular subtypes of MPM, we focus on the tumor suppressor gene , a member of the Hippo signaling pathway, which plays a key role in mesothelial carcinogenesis. Sixty-one MPM primary cultures established in our laboratory were screened for mutations in Gene inactivation was modeled using siRNAs. Gene and protein expressions were analyzed by quantitative RT-PCR, Western blot analysis, and reverse phase protein array. Cell proliferation, viability, apoptosis, mobility, and invasion were determined after siRNA knockdown or YAP (verteporfin), mTOR (rapamycin), and mTOR/PI3K/AKT (PF-04691502) inhibitor treatment. The gene was altered in 11% of MPM by point mutations and large exon deletions. Genetic data coupled with transcriptomic data allowed the identification of a new MPM molecular subgroup, C2, characterized by a co-occurring mutation in the and genes in the same MPM. MPM patients of this subgroup presented a poor prognosis. Coinactivation of and leads to loss of cell contact inhibition between MPM cells. Hippo signaling pathway activity, mTOR expression, and phosphorylation were altered in the C2 MPM subgroup. MPMs of this new subgroup show higher sensitivity to PF-04691502 inhibitor. The gene was identified as a potential biomarker of the C2 MPM subgroup and PF-04691502 sensitivity. We identified a new MPM molecular subgroup that shares common genetic and transcriptomic characteristics. Our results made it possible to highlight a greater sensitivity to an anticancer compound for this MPM subgroup and to identify a specific potential biomarker. .

Malignant pleural mesothelioma (MPM) is a very aggressive tumor with no known curative treatment. Better knowledge of the molecular mechanisms of mesothelial carcinogenesis is required to develop new therapeutic strategies. MPM, like all cancer cells, needs to maintain telomere length to prevent senescence. Previous studies suggested that the telomere lengthening mechanism in MPM is based mainly on telomerase activity. For this reason, we focused on the key catalytic enzyme, TERT (telomerase reverse transcriptase), by analyzing its gene expression in MPM and by studying the mechanism underlying its upregulation. We used our large collection of MPM composed of 61 MPM in culture and 71 frozen MPM tumor samples. Evaluation of TERT mRNA expression by quantitative RT-PCR showed overexpression in MPM in culture compared with normal mesothelial cells, and in MPM tumor samples compared with normal pleura. We identified a 'hot spot' of mutations in the TERT gene core promoter in both MPM in culture and in MPM tumor samples with an overall frequency of 15%. Furthermore, data clearly identified mutation in the TERT promoter as a mechanism of TERT mRNA upregulation in MPM. In contrast, gene copy number amplification was not associated with TERT overexpression. Then, we analyzed the clinicopathological, etiological and genetic characteristics of MPM with mutations in the TERT promoter. TERT promoter mutations were more frequent in MPM with sarcomatoid histologic subtype (P<0.01), and they were frequently associated with CDKN2A gene inactivation (P=0.03). In conclusion, a subgroup of MPM presents TERT promoter mutations, which lead to TERT mRNA upregulation. This is the first recurrent gain-of-function oncogenic mutations identified in MPM.