Expression, enzyme activity, and subcellular localization of mammalian target of rapamycin in insulin-responsive cells.

Journal Article (Journal Article)

The role of the mammalian target of rapamycin (mTOR) was investigated in insulin responsive cell lines. mTOR was expressed at high levels in insulin responsive cell types and in 3T3-L1 cells mTOR expression levels increased dramatically as cells differentiated from fibroblasts into insulin responsive adipocytes. mTOR localized to membrane fractions in all cells tested and in 3T3-L1 adipocytes mTOR was specifically localized to microsomal membranes. Protein kinase activity directed towards mTOR was tightly associated with mTOR immunoprecipitates and this kinase activity was inhibited by FKBP12-rapamycin indicating it was due to an autokinase activity present in mTOR. The mTOR autokinase and the protein kinase activity of the p110 alpha isoform of PI 3-kinase shared several notable similarities; (a) both were maximally active in the presence of Mn2+ but also showed significant activity in the presence of Mg2+ (b) neither were inhibited by the presence of non-ionic detergent and (c) both were inhibited by wortmannin and LY294002, known inhibitors of the PI 3-kinase lipid kinase activity. These data taken together indicate the autokinase activity lay in the PI 3-kinase homology domain. In summary mTOR is a membrane anchored protein kinase that is active in conditions encountered in vivo and the fact it is highly expressed in insulin responsive cell types is consistent with a role in insulin signalling.

Full Text

Duke Authors

Cited Authors

  • Withers, DJ; Ouwens, DM; Nave, BT; van der Zon, GC; Alarcon, CM; Cardenas, ME; Heitman, J; Maassen, JA; Shepherd, PR

Published Date

  • December 29, 1997

Published In

Volume / Issue

  • 241 / 3

Start / End Page

  • 704 - 709

PubMed ID

  • 9434772

International Standard Serial Number (ISSN)

  • 0006-291X

Digital Object Identifier (DOI)

  • 10.1006/bbrc.1997.7878


  • eng

Conference Location

  • United States