Mutation of the PI3' kinase gene in a human colon carcinoma cell line, HCC2998.
HCC2998 is a highly differentiated human colon carcinoma cell line, which has been shown to be converted to a poorly differentiated one after expression of a constitutively active phosphatidylinositol 3-kinase (PI3' kinase). These cells express aberrant sizes of a regulatory subunit of PI3' kinase, p85alpha, with molecular weights of 50 and 76 kDa at a very low level. To elucidate how these cells express these proteins, we analyzed mutations within the p85alpha gene. DNA sequencing analysis revealed that these mutant proteins were generated by independent point mutations in the two alleles of the p85alpha gene: one in the coding sequence, and the other in the acceptor sequence for splicing. Introduction of wild-type p85alpha into HCC2998 cells induced slight rounding of the cells and enhancement of mucin secretion. At the same time, a membrane receptor, ErbB3, was phosphorylated on tyrosine, which in turn, binds to PI3' kinase. Since ErbB3 is upstream of PI3' kinase, it is likely that there is an autocrine loop in which PI3' kinase is activated by ErbB3, which may contribute to dedifferentiation of the cells.
Shi
Bin-Hi
BH
Laboratory of Biological Chemistry, Division of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo, Japan.
Nashimoto
Takeshi
T
Andoh
Ryota
R
Konishi
Hiroaki
H
Kobayashi
Michimoto
M
Xu
Qingyun
Q
Ihara
Sayoko
S
Fukui
Yasuhisa
Y
D000483:Alleles; D001483:Base Sequence; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D003001:Cloning, Molecular; D003110:Colonic Neoplasms / Q000201:enzymology* / Q000235:genetics* / Q000473:pathology; D004252:DNA Mutational Analysis; D004273:DNA, Neoplasm / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009077:Mucins / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry / Q000235:genetics*; D010766:Phosphorylation; D017354:Point Mutation; D021122:Protein Subunits; D020893:Receptor, ErbB-3 / Q000737:chemistry / Q000378:metabolism; D014443:Tyrosine / Q000737:chemistry
D004273:DNA, Neoplasm; D009077:Mucins; D021122:Protein Subunits; D014443:Tyrosine; D019869:Phosphatidylinositol 3-Kinases; D020893:Receptor, ErbB-3