Oncogenic KRAS and BRAF differentially regulate hypoxia-inducible factor-1alpha and -2alpha in colon cancer.
KRAS and BRAF mutations are frequently observed in human colon cancers. These mutations occur in a mutually exclusive manner, and each is associated with distinctive biological features. We showed previously that K-ras can interact with hypoxia to activate multiple signaling pathways. Many hypoxic responses are mediated by hypoxia-inducible factor (HIF)-1alpha and HIF-2alpha, and we sought to define the roles of mutant KRAS and BRAF in the induction of HIF-1alpha and HIF-2alpha in colon cancer cells. Ectopic expression of mutant K-ras in Caco2 cells enhanced the hypoxic induction of only HIF-1alpha, whereas mutant BRAF enhanced both HIF-1alpha and HIF-2alpha. Knockout or knockdown of mutant KRAS in DLD-1 and HCT116 cells impaired the hypoxic induction of only HIF-1alpha. HIF-1alpha mRNA levels were comparable in cells with and without a KRAS mutation. However, the rate of HIF-1alpha protein synthesis was higher in cells with a KRAS mutation, and this was suppressed by the phosphoinositide 3-kinase inhibitor LY294002. In contrast, knockdown of mutant BRAF in HT29 cells suppressed both HIF-1alpha and HIF-2alpha. Although BRAF regulated mRNA levels of both HIF-1alpha and HIF-2alpha, knockdown of BRAF or treatment with the MEK inhibitor PD98059 impaired the translation of only HIF-2alpha. Our data reveal that oncogenic KRAS and BRAF mutations differentially regulate the hypoxic induction of HIF-1alpha and HIF-2alpha in colon cancer, and this may potentially contribute to the phenotypic differences of KRAS and BRAF mutations in colon tumors.
Gastrointestinal Unit and Cancer Center, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114, USA.
Hirotoshi
H
Kikuchi
Maria S
MS
Pino
Min
M
Zeng
Senji
S
Shirasawa
Daniel C
DC
Chung
D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D000860:Hypoxia; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics*; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics*; D016283:Proto-Oncogene Proteins p21(ras); D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018631:ras Proteins / Q000235:genetics*; D000099162:Endothelial PAS Domain-Containing Protein 1
D051792:Basic Helix-Loop-Helix Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D019869:Phosphatidylinositol 3-Kinases; D011518:Proto-Oncogene Proteins; D048493:Proto-Oncogene Proteins B-raf; D016283:Proto-Oncogene Proteins p21(ras); D012333:RNA, Messenger; D018631:ras Proteins; D000099162:Endothelial PAS Domain-Containing Protein 1; C497442:HIF1A protein, human; C117307:KRAS protein, human; C482119:BRAF protein, human