Open AccessRas oncogene induces β‐galactoside α2,6‐sialyltransferase (ST6Gal I) via a RalGEF‐mediated signal to its housekeeping promoter
Author(s) -
Dalziel Martin,
Dall'Olio Fabio,
Mungul Arron,
Piller Véronique,
Piller Friedrich
Publication year - 2004
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.2004.04284.x
Subject(s) - sialyltransferase , microbiology and biotechnology , transfection , biology , promoter , transcription (linguistics) , oncogene , gene expression , gene , chemistry , cell cycle , glycoprotein , genetics , linguistics , philosophy
Several oncogenic proteins are known to influence cellular glycosylation. In particular, transfection of codon 12 point mutated H‐Ras increases CMP‐Neu5Ac: Galβ1,4GlcNAc α2,6‐sialyltransferase I (ST6Gal I) activity in rodent fibroblasts. Given that Ras mediates its effects through at least three secondary effector pathways (Raf, RalGEFs and PI3K) and that transcriptional control of mouse ST6Gal I is achieved by the selective use of multiple promoters, we attempted to identify which of these parameters are involved in linking the Ras signal to ST6Gal I gene transcription in mouse fibroblasts. Transformation by human K‐Ras or H‐Ras (S12 and V12 point mutations, respectively) results in a 10‐fold increase in ST6Gal I mRNA, but no alteration in the expression of related sialyltransferases. Using an inducible H‐Ras V12 expression system, a direct causal link between activated H‐Ras expression and elevated ST6Gal I mRNA was demonstrated. The accumulation of the ST6Gal I transcript in response to activated Ras was accompanied by an increase of α2,6‐sialyltransferase activity and of Neu5Acα2,6Gal at the cell surface. Results obtained with H‐Ras V12 partial loss of function mutants H‐Ras V12S35 (Raf signal only), H‐Ras V12C40 (PI3‐kinase signal only) and H‐Ras V12G37 (RalGEFs signal only) suggest that the H‐Ras induction of the mouse ST6Gal I gene ( Siat1 ) transcription is primarily routed through RalGEFs. 5′‐Rapid amplification of cDNA ends analysis demonstrated that the increase in ST6Gal I mRNA upon H‐Ras V12 or K‐Ras S12 transfection is mediated by the Siat1 housekeeping promoter P3‐associated 5′ untranslated exons.