Functional Characterization of TMEM127 Variants Reveals Novel Insights into Its Membrane Topology and Trafficking

J Clin Endocrinol Metab. 2020 Sep 1;105(9):e3142-e3156. doi: 10.1210/clinem/dgaa396.


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.

Keywords: TMEM127; endocytic motif; germline variant; paraganglioma; pheochromocytoma; transmembrane protein; tumor suppressor gene; variant classification.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

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


  • Membrane Proteins
  • TMEM127 protein, human