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.
Kikuchi
Hirotoshi
H
Gastrointestinal Unit and Cancer Center, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114, USA.
Pino
Maria S
MS
Zeng
Min
M
Shirasawa
Senji
S
Chung
Daniel C
DC
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