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

Abstract

Ras is activated by transforming growth factor beta (TGFbeta) in several cell types, but the biological consequences of this activation are largely unknown. We now show that ras mediates two stages in integrin beta1-chain maturation: 1) glycosylation of the 86-kD core peptide, which is a TGFbeta1-independent process, and 2) TGFbeta1-mediated conversion of the 115-kD beta1 integrin precursor into the mature 130-kD form. HD3 colon epithelial cells maintain elevated levels of integrin alpha2beta1 heterodimers, strong binding to collagen I, and autocrine regulation by TGFbeta1, which converts beta1 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 beta1-chain, decreased cell surface expression of the mature integrin beta1, and impaired binding to collagen and laminin. Autocrine levels of TGFbeta were not altered by expression of N17ras. The aberrant glycosylation of the integrin beta1-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 TGFbeta1 or inhibition of autocrine TGFbeta1. In contrast, conversion of the partially glycosylated beta1 integrin precursor into the mature 130-kD isoform was accelerated by exogenous TGFbeta1 and blocked by neutralizing antibody to autocrine TGFbeta1 in control cell lines. Neither effect was seen in the N17ras transfectants, indicating that TGFbeta1 modulates integrin beta1-chain maturation by activating ras proteins. Cell fractionation studies demonstrated that this conversion takes place within the Golgi.

Oncogenic Ki-ras Confers a More Aggressive Colon Cancer Phenotype through Modification of Transforming Growth Factor-β Receptor III

“…The TGF-␤1/Ras pathway functions to convert a partially glycosylated ␤ 1 integrin precursor into the mature, fully glycosylated form and is blocked by dominant-negative N17Ras (58). In like fashion, constitutive activation of Ki-Ras in stable oncogenic Ki-ras transfectants may up-regulate glycosyltransferases that modify T␤RIII.…”

“…In this study, we have shown that both functional, posttranslationally modified T␤RIII and the biological response to TGF-␤1 were restored by stable expression of oncogenic Ki- (58). The TGF-␤1/Ras pathway functions to convert a partially glycosylated ␤ 1 integrin precursor into the mature, fully glycosylated form and is blocked by dominant-negative N17Ras (58).…”

TGF-β1 -promoted epithelial-to-mesenchymal transformation and cell adhesion contribute to TGF-β1 -enhanced cell migration in SMMC-7721 cells

“…The hypoglycosylated form (lower band in Fig 4C) was tentatively identified as biosynthetic precursor of 1 subunit. The band with lower migration rate (upper band in Fig 4C) was the hyperglycosylated mature form of integrin 1 subunit, which mainly located at the plasma membrane [21][22][23]. The correlation between 5 1 integrin and cell migration has been previously reported.…”

Core3 O-Glycan Synthase Suppresses Tumor Formation and Metastasis of Prostate Carcinoma PC3 and LNCaP Cells through Down-regulation of α2β1 Integrin Complex

“…9C). It was reported that the higher molecular weight form represents the mature form of ␤1 integrin (42). Two differently glycosylated forms of ␤1 integrin resolved to one lower molecular weight band after N-glycanase treatment (Fig.…”