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Mol. Cell. Biol., 03 1995, 1613-1619, Vol 15, No. 3
N Asai, T Iwashita, M Matsuyama and M Takahashi
Transforming activity of the c-ret proto-oncogene with multiple endocrine
neoplasia (MEN) 2A mutations was investigated by transfection of NIH 3T3
cells. Mutant c-ret genes driven by the simian virus 40 or cytomegalovirus
promoter induced transformation with high efficiencies. The 170-kDa Ret
protein present on the cell surface of transformed cells was highly
phosphorylated on tyrosine and formed disulfide-linked homodimers. This
result indicated that MEN 2A mutations induced ligand- independent
dimerization of the c-Ret protein on the cell surface, leading to
activation of its intrinsic tyrosine kinase. In addition to the MEN 2A
mutations, we further introduced a mutation (lysine for asparaginic acid at
codon 300 [D300K]) in a putative Ca(2+)-binding site of the cadherin-like
domain. When c-ret cDNA with both MEN 2A and D300K mutations was
transfected into NIH 3T3 cells, transforming activity drastically
decreased. Western blot (immunoblot) analysis revealed that very little of
the 170-kDa Ret protein with the D300K mutation was expressed in
transfectants while expression of the 150-kDa Ret protein retained in the
endoplasmic reticulum was not affected. This result also demonstrated that
transport of the Ret protein to the plasma membrane is required for its
transforming activity.
Copyright © 1995, American Society for Microbiology
Mechanism of activation of the ret proto-oncogene by multiple endocrine neoplasia 2A mutations
Department of Pathology, Nagoya University School of Medicine, Japan.
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