TAILIEUCHUNG - Báo cáo khoa học: Ras oncogene induces b-galactoside a2,6-sialyltransferase (ST6Gal I) via a RalGEF-mediated signal to its housekeeping promoter

Several oncogenic proteins are known to influence cellular glycosylation. In particular, transfection of codon 12 point mutated H-Ras increases CMP-Neu5Ac: Galb1,4GlcNAc a2,6-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 ofmouse ST6Gal I is achieved by the selective use of multiple promoters, we attempted to identifywhichof these parameters are involved in linking the Ras signal to ST6Gal I gene transcription in mouse fibroblasts. . | Eur. J. Biochem. 271 3623-3634 2004 FEBS 2004 doi Ras oncogene induces b-galactoside a2 6-sialyltransferase ST6Gal I via a RalGEF-mediated signal to its housekeeping promoter Martin Dalziel1 Fabio Dall Olio2 Arron Munaul3 Veroniaue Piller1 and Friedrich Piller1 1 Centre de Biophysique Moléculaire CNRS UPR 4301 affiliated with the University of Orleans and INSERM Orleans France 2Dipartimento di Patologia Sperimentale Universita di Bologna Italy 3Cancer Research UK Breast Cancer Biology Group Guy s Hospital London UK Several oncogenic proteins are known to influence cellular glycosylation. In particular transfection of codon 12 point mutated H-Ras increases CMP-Neu5Ac Galp1 4GlcNAc a2 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-RasV12 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 a2 6-sialyltransferase activity and of Neu5Aca2 6Gal at the cell surface. Results obtained with H-RasV12 partial loss of function mutants H-RasV12S35 Raf signal only H-RasV12C40 PI3-kinase signal only and H-RasV12G37 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 .

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