A highly expressed 81 kDa protein in immortalized mouse fibroblast: its proliferative function and identity with ezrin.
An 81 kDa protein was found to be highly expressed in spontaneously immortalized CD1-ICR mouse fibroblasts, RS-4, as compared to normal fibroblasts. RS-4 cells have a reduced serum requirement and exhibit multilayered growth in vitro but are not tumorigenic. The protein was purified from RS-4 cell extracts and used to obtain a polyclonal antibody that specifically immunoprecipitated an 81 kDa protein from cell lysates. Immunocloning of its cDNA and sequence analysis revealed its identity with ezrin, an F-actin binding protein that is a component of the cortical cytoskeleton. Microinjection of the purified IgG fraction of the anti-p81 antiserum into the cytoplasm of RS-4 cells blocked their entry into S phase suggesting that the protein has a proliferative function. Immunostaining of normal mouse tissues showed that the expression of p81/ezrin was highest in proliferating cell populations. Unlike RS-4, NIH3T3 cells exhibit contact inhibition and express levels of p81/ezrin similar to those of normal fibroblasts. When NIH3T3 cells were transfected with p81/ezrin cDNA they lost contact inhibition and thus resembled RS-4 cells. The study demonstrates a proliferative function of p81/ezrin and suggests its involvement in pathways that negatively regulate contact inhibition.
Kaul
S C
SC
National Institute of Bioscience and Human Technology, Agency of Industrial Science and Technology, Tsukuba, Ibaraki, Japan.
Mitsui
Y
Y
Komatsu
Y
Y
Reddel
R R
RR
Wadhwa
R
R
D016475:3T3 Cells / Q000166:cytology; D000818:Animals; D002450:Cell Communication / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins; D018076:DNA, Complementary / Q000235:genetics; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008813:Mice, Inbred ICR; D008845:Microinjections; D010750:Phosphoproteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D010957:Plasmids; D014162:Transfection; D000099149:Ezrin
D003598:Cytoskeletal Proteins; D018076:DNA, Complementary; D010750:Phosphoproteins; D000099149:Ezrin