Ras oncogene induces beta-galactoside alpha2,6-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: Galbeta1,4GlcNAc alpha2,6-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 alpha2,6-sialyltransferase activity and of Neu5Acalpha2,6Gal 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 demonstrated that the increase in ST6Gal I mRNA upon H-RasV12 or K-RasS12 transfection is mediated by the Siat1 housekeeping promoter P3-associated 5' untranslated exons.
Dalziel
Martin
M
Centre de Biophysique Moléculaire, CNRS UPR 4301 affiliated with the University of Orléans and INSERM, Orléans, France.
Dall'Olio
Fabio
F
Mungul
Arron
A
Piller
Véronique
V
Piller
Friedrich
F
D016475:3T3 Cells; D000818:Animals; D045744:Cell Line, Tumor; D002874:Chromosome Mapping; D003062:Codon; D005091:Exons; D005347:Fibroblasts / Q000201:enzymology / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D011905:Genes, ras; D006801:Humans; D051379:Mice; D041681:NIH 3T3 Cells; D017354:Point Mutation; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D012799:Sialyltransferases / Q000235:genetics* / Q000378:metabolism*; D015398:Signal Transduction; D014158:Transcription, Genetic; D020726:ral Guanine Nucleotide Exchange Factor / Q000378:metabolism*; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase
D003062:Codon; D012333:RNA, Messenger; D020726:ral Guanine Nucleotide Exchange Factor; D012799:Sialyltransferases; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase