Mutational and functional study of Tuberous Sclerosis Complex 1 and 2 genes (TSC1 and TSC2)

• Autor(a) principal: Almeida, Luiz Gustavo Dufner de
• Data de Publicação: 2019
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: http://www.teses.usp.br/teses/disponiveis/41/41131/tde-27082019-100610/
• topic: Complexo da esclerose tuberosa; Estudo funcional; Functional study; Gene TSC1; Gene TSC2; Transcriptoma; Transcriptome; TSC1 gene; TSC2 gene; Tuberous Sclerosis Complex

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder caused by pathogenic variants in either TSC1 or TSC2 tumor suppressor genes. It affects more often the brain, skin, kidneys, heart, lungs, and retina. The protein products of both genes, TSC1 (hamartin) and TSC2 (tuberin), interact, assembling a complex that inhibits mTORC1. Cells with bi-allelic inactivation of either TSC1 or TSC2 genes present hyperactivation of mTORC1, which phosphorylates downstream targets, up-regulating cell proliferation and growth. Moreover, a functional role as heat-shock protein (HSP) co-chaperone has been assigned to TSC1 protein. The first aim of the thesis was to analyze the nature, distribution and functional effects of TSC1 and TSC2 DNA variants from 100 patients with definite clinical diagnosis of TSC. We analyzed leukocyte DNA of 115 TSC patients from three Brazilian tertiary referral hospitals. Pathogenic DNA variants were detected in 99 (86,09%) unrelated individuals; 17 (17,17%) in TSC1 and 82 (82,82%) in TSC2. Clear loss-of-function mutations were detected in 87 patients, of which frameshift (29.29%) and nonsense (29.29%) variants were the most common types. In- frame deletions, missense and putative splicing DNA variants with uncertain clinical significance (VUS) have been functionally assessed. Five variants significantly increased phosphorylation of the reporter residue S6K Thr 389 . Forty-one novel pathogenic DNA variants and 19 novel single nucleotide variants have been detected. Among the 11 individuals with no mutation identified, seven presented rare putative missense, splicing or in- frame deletion DNA VUS. To understand the regulatory relationship of TSC1/2 gene expression, we aimed to evaluate TSC1 and TSC2 mRNA and protein levels in human cell lines with bi-allelic inactivation of each gene. We employed high throughput transcriptome analysis (RNA-Seq) and Western blotting of HEK293T and other six HEK293T-derived cell lines that had the genomic sequence of the TSC1 and or TSC2 genes edited by the CRISPR (clustered regularly interspaced short palindromic repeats)-CAS9 system. In lack of either TSC1 or TSC2 protein, a significant reduction of the respective mRNA was observed, inferring no positive transcriptional feedback. Serum-deprived cell lines without TSC1 decreased TSC2 mRNA levels. Under these conditions, TSC1 mRNA levels were not negatively affected by the lack of TSC2. In one cell line with loss of TSC1 (1C2) TSC1/2 mRNA and TSC2 protein levels were consistently decreased independently on serum. RNA-Seq gene ontology analyses comparing 1C2 to HEK293T reference cell line disclosed down-regulation of translational pathways independently on serum; and up-regulation of protein folding and stability pathways upon serum withdrawal. Our data are consistent with the role of TSC1 as HSP co-chaperone, and suggest that TSC1 mRNA may be regulated at both transcriptional and decay levels