Functional analysis of PIK3CA gene mutations in human colorectal cancer.
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.
Ikenoue
Tsuneo
T
Department of Gastroenterology, Graduate School of Medicine, University of Tokyo Hospital, Bunkyo-ku, Japan.
Kanai
Fumihiko
F
Hikiba
Yohko
Y
Obata
Toshiyuki
T
Tanaka
Yasuo
Y
Imamura
Jun
J
Ohta
Miki
M
Jazag
Amarsanaa
A
Guleng
Bayasi
B
Tateishi
Keisuke
K
Asaoka
Yoshinari
Y
Matsumura
Masayuki
M
Kawabe
Takao
T
Omata
Masao
M
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
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