Effects of SETD2 on telomere length and malignant transformation property of Met-5A after one-month crocidolite exposure.

Crocidolite is a carcinogen contributing to the pathogenesis of malignant mesothelioma. This study aimed to characterize the possible telomere-related events mediating the malignant transformation of mesothelial cells with and without SETD2 under crocidolite exposure. The crocidolite concentration resulting in 90% viable SETD2 knockout Met-5A (Met-5A^SETD2-KO) and Met-5A were estimated to be 0.71 μg/cm² and 1.8 μg/cm², respectively, during 72 h of exposure, which was further employed in chronical crocidolite exposure during a 72 h exposure interval per time up to 1 month. Chronical crocidolite-exposed Met-5A^SETD2-KO (chronical Cro-Met-5A^SETD2-KO) had higher colony formation and increased telomerase reverse transcriptase (TERT) protein levels than chronical crocidolite-exposed Met-5A (chronical Cro-Met-5A) and Met-5A^SETD2-KO. Chronical Cro-Met-5A^SETD2-KO had longer telomere length (TL) than chronical Cro-Met-5A, although there were no changes in TL for either chronical Cro-Met-5A or chronical Cro-Met-5A^SETD2-KO compared with their corresponding cells without crocidolite exposure. BIBR 1532, an inhibitor targeting TERT, partially reduced colony formation and TL for chronical Cro-Met-5A^SETD2-KO, while BIBR 1532 reduced TL but had no effect on colony formation for chronical Cro-Met-5A. Therefore, SETD2 deficient mesothelial cells are susceptible to malignant transformation during chronical crocidolite exposure, and TERT-dependent TL modification likely partially drives SETD2 loss-mediated early onset of mesothelial malignant transformation.