Steps in integrin β1-chain glycosylation mediated by TGFβ1 signaling through ras

Academic Article

Abstract

  • Ras is activated by transforming growth factor beta (TGFβ) in several cell types, but the biological consequences of this activation are largely unknown. We now show that ras mediates two stages in integrin β1-chain maturation: 1) glycosylation of the 86-kD core peptide, which is a TGFβ1- independent process, and 2) TGFβ1-mediated conversion of the 115-kD β1 integrin precursor into the mature 130-kD form. HD3 colon epithelial cells maintain elevated levels of integrin α2β1 heterodimers, strong binding to collagen I, and autocrine regulation by TGFβ1, which converts β1 integrin into the mature cell surface form. Each of three HD3 cell clones that stably express dominant negative ras (N17ras) exhibited abnormal glycosylation of the integrin β1-chain, decreased cell surface expression of the mature integrin β1, and impaired binding to collagen and laminin. Autocrine levels of TGFβ were not altered by expression of N17ras. The aberrant glycosylation of the integrin β1-chain was reversed by antisense oligonucleotides specific to the DNA sequence encoding the rasS17N mutation. Glycosylation of the 86-kD core peptide was delayed in the N17ras transfectants, but was not altered by either the addition of TGFβ1 or inhibition of autocrine TGFβ1. In contrast, conversion of the partially glycosylated β1 integrin precursor into the mature 130-kD isoform was accelerated by exogenous TGFβ1 and blocked by neutralizing antibody to autocrine TGFβ1 in control cell lines. Neither effect was seen in the N17ras transfectants, indicating that TGFβ1 modulates integrin β1-chain maturation by activating ras proteins. Cell fractionation studies demonstrated that this conversion takes place within the Golgi.
  • Published In

    Author List

  • Bellis SL; Newman E; Friedman EA
  • Start Page

  • 33
  • End Page

  • 44
  • Volume

  • 181
  • Issue

  • 1