Expression of stress response protein glucose regulated protein-78 mediated by c-Myb.
Glucose regulated protein-78, GRP78 has been implicated in the protection of tumor cells from cytotoxic damage and apoptosis. When protein profiles of colon cell lines were investigated we found remarkably high GRP78 expression in two cell lines. These cell lines express elevated levels of the transcription factor c-Myb due to genomic amplification of the c-myb locus and we hypothesized that c-Myb regulates GRP78 expression in colon cancer cells. The promoters of human and murine GRP78 and the related family member GRP94 were examined and potential c-Myb binding sites were identified and characterized. DNA binding studies with recombinant c-Myb and nuclear extracts together with ChIP assays on colon cell lines validated these sites. Endogenous GRP78 expression was further induced in these colon cells in response to Thapsigargin treatment, a potent inducer of the unfolded protein response. Transactivation studies with the human GRP78 promoter in colon cell lines showed reporter activity was dependent upon the presence of a conserved c-Myb binding site independent of sequences associated with the unfolded protein response. Finally, over-expression of c-Myb induced the endogenous GRP78 gene. These data suggest that amplification of c-myb in tumor cells may lead to robust GRP78 gene induction, which may in turn assist cells in survival under conditions of oxygen deprivation and nutrient stress.
Ramsay
Robert G
RG
Differentiation and Transcription Laboratory, Trescowthick Research Laboratories, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne 3002, Australia. rob.ramsay@petermac.org
Ciznadija
Daniel
D
Mantamadiotis
Theo
T
Anderson
Robin
R
Pearson
Richard
R
D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D000091342:Endoplasmic Reticulum Chaperone BiP; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D020570:Genes, myb; D006360:Heat-Shock Proteins / Q000096:biosynthesis*; D006801:Humans; D018832:Molecular Chaperones / Q000096:biosynthesis*; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000235:genetics*; D019284:Thapsigargin / Q000494:pharmacology; D015533:Transcriptional Activation
D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D019284:Thapsigargin