title: Functional analysis of PIK3CA gene mutations in human colorectal cancer.
abstract: Mutations in the PIK3CA gene, which encodes the p110alpha catalytic subunit of phosphatidylinositol 3-kinase (PI3K), have been reported in human cancers, including colorectal cancer. Most of the mutations cluster at hotspots within the helical and kinase domains. Whereas H1047R, one of the hotspot mutants, is reported to have elevated lipid kinase activity, the functional consequences of other mutations have not been examined. In this study, we examined the effects of colon cancer-associated PIK3CA mutations on the lipid kinase activity in vitro, activation of the downstream targets Akt and p70S6K in vivo and NIH 3T3-transforming ability. Of eight mutations examined, all showed increased lipid kinase activity compared with wild-type p110alpha. All the mutants strongly activated Akt and p70S6K compared with wild-type p110alpha as determined by immunoblotting using phospho-specific antibodies. These mutants also induced morphologic changes, loss of contact inhibition, and anchorage-independent growth of NIH 3T3 cells. The hotspot mutations examined in this study, E542K, E545K, and H1047R, all had high enzymatic and transforming activities. These results show that almost all the colon cancer-associated PIK3CA mutations are functionally active so that they are likely to be involved in carcinogenesis.
authors.affiliation: Department of Gastroenterology, Graduate School of Medicine, University of Tokyo Hospital, Bunkyo-ku, Japan.
authors.forename: Tsuneo
authors.initials: T
authors.lastname: Ikenoue
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Kanai
authors.forename: Yohko
authors.initials: Y
authors.lastname: Hikiba
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Obata
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Tanaka
authors.forename: Jun
authors.initials: J
authors.lastname: Imamura
authors.forename: Miki
authors.initials: M
authors.lastname: Ohta
authors.forename: Amarsanaa
authors.initials: A
authors.lastname: Jazag
authors.forename: Bayasi
authors.initials: B
authors.lastname: Guleng
authors.forename: Keisuke
authors.initials: K
authors.lastname: Tateishi
authors.forename: Yoshinari
authors.initials: Y
authors.lastname: Asaoka
authors.forename: Masayuki
authors.initials: M
authors.lastname: Matsumura
authors.forename: Takao
authors.initials: T
authors.lastname: Kawabe
authors.forename: Masao
authors.initials: M
authors.lastname: Omata
mesh_terms: D000818:Animals; D014408:Biomarkers, Tumor / Q000235:genetics; D002448:Cell Adhesion / Q000502:physiology; D048708:Cell Growth Processes / Q000502:physiology; D058534:Class I Phosphatidylinositol 3-Kinases; D015179:Colorectal Neoplasms / Q000201:enzymology* / Q000235:genetics; D004789:Enzyme Activation; D006801:Humans; D051379:Mice; D041681:NIH 3T3 Cells; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics* / Q000378:metabolism; D011487:Protein Conformation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism
chemical_list: D014408:Biomarkers, Tumor; D058534:Class I Phosphatidylinositol 3-Kinases; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; C484760:PIK3CA protein, human; C494918:AKT1 protein, human