Title: Functional Characterization of TMEM127 Variants Reveals Novel Insights into Its Membrane Topology and Trafficking.
Authors: Flores, Shahida K; Deng, Yilun; Cheng, Ziming; Zhang, Xingyu; Tao, Sifan; Saliba, Afaf; Chu, Irene; Burnichon, Nelly; Gimenez-Roqueplo, Anne-Paule; Wang, Exing; Aguiar, Ricardo C T; Dahia, Patricia L M
Published In J Clin Endocrinol Metab, (2020 09 01)
Abstract: CONTEXT: TMEM127 is a poorly known tumor suppressor gene associated with pheochromocytomas, paragangliomas, and renal carcinomas. Our incomplete understanding of TMEM127 function has limited our ability to predict variant pathogenicity. PURPOSE: To better understand the function of the transmembrane protein TMEM127 we undertook cellular and molecular evaluation of patient-derived germline variants. DESIGN: Subcellular localization and steady-state levels of tumor-associated, transiently expressed TMEM127 variants were compared to the wild-type protein using immunofluorescence and immunoblot analysis, respectively, in cells genetically modified to lack endogenous TMEM127. Membrane topology and endocytic mechanisms were also assessed. RESULTS: We identified 3 subgroups of mutations and determined that 71% of the variants studied are pathogenic or likely pathogenic through loss of membrane-binding ability, stability, and/or internalization capability. Investigation into an N-terminal cluster of missense variants uncovered a previously unrecognized transmembrane domain, indicating that TMEM127 is a 4- transmembrane, not a 3-transmembrane domain-containing protein. Additionally, a C-terminal variant with predominant plasma membrane localization revealed an atypical, extended acidic, dileucine-based motif required for TMEM127 internalization through clathrin-mediated endocytosis. CONCLUSION: We characterized the functional deficits of several germline TMEM127 variants and identified novel structure-function features of TMEM127. These findings will assist in determining pathogenicity of TMEM127 variants and will help guide future studies investigating the cellular role of TMEM127.
PubMed ID: 32575117
MeSH Terms: Adrenal Gland Neoplasms/genetics; Adrenal Gland Neoplasms/metabolism; Amino Acid Substitution; Cell Membrane/metabolism*; Gene Knockdown Techniques; Genetic Predisposition to Disease; Germ-Line Mutation; HEK293 Cells; Humans; Membrane Proteins/chemistry; Membrane Proteins/genetics*; Membrane Proteins/metabolism*; Mutagenesis, Site-Directed; Mutation*/physiology; Paraganglioma/genetics; Paraganglioma/metabolism; Pheochromocytoma/genetics; Pheochromocytoma/metabolism; Protein Transport/genetics; Tissue Distribution