Role of Klotho Protein in Tumor Genesis, Cancer Progression, and Prognosis in Patients with High-Grade Glioma

Abstract

Klotho, a single-pass transmembrane protein associated with premature aging, acts as a tumor suppressor gene by inhibiting insulin/insulin-like growth factor-1 and fibroblast growth factor pathways. Downregulated Klotho expression is reported in melanoma, mesothelioma, bladder, breast, gastric, cervix, lung, and kidney cancers and is associated with a poor prognosis. Klotho expression and Klotho promoter hypermethylation are predictive factors for patient prognosis. To investigate the potential role of Klotho in glioblastoma-multiforme (GBM), 22 GBM samples were collected from the Sheba Tumor Bank and examined. We found that increased Klotho messenger ribonucleic acid (RNA) expression predicted longer survival (P= 0.03) of GBM patients. Methylation analysis was performed on bisulfite-treated deoxyribonucleic acid from the GBM patient samples using ionization time-of-flight mass spectrometry according to the Sequenom EpiTYPER protocols. Klotho promoter hypermethylation was detected in 65% of the GBM samples and correlated significantly with improved survival (P < 0.04). We found 3 major Klotho promotor hypermethylation sites located 585-579 bp, 540-533 bp, and 537-534 bp upstream of the transcription start site. Methylated deoxyribonucleic acid immunoprecipitation studies confirmed these results. Notably, the messenger RNA expression in these GBM samples revealed an unexpected linear correlation with methylation of these 3 hypermethylation sites identified in the Klotho promotor. Thus Klotho expression and methylation could predict prognosis in patients with GBM. Epigenetic regulation in GBM appears to be complicated. Specific CpG islands affect genes or micro RNAs that interact to control Klotho expression. The diverse effects of these islands may be due to unique factors of GBM.