Sc. Kaul et al., A HIGHLY-EXPRESSED 81-KDA PROTEIN IN IMMORTALIZED MOUSE FIBROBLASTS -ITS PROLIFERATIVE FUNCTION AND IDENTITY WITH EZRIN, Oncogene, 13(6), 1996, pp. 1231-1237
An 81 kDa protein was found to be highly expressed in spontaneously im
mortalized CD1-ICR mouse fibroblasts, RS-4, as compared to normal fibr
oblasts. RS-4 cells have a reduced serum requirement and exhibit multi
layered growth in vitro but are not tumorigenic, The protein was purif
ied from RS-4 cell extracts and used to obtain a polyclonal antibody t
hat specifically immunoprecipitated an 81 kDa protein from cell lysate
s. Immunocloning of its cDNA and sequence analysis revealed its identi
ty with ezrin, an F-actin binding protein that is a component of the c
ortical cytoskeleton, Microinjection of the purified IgG fraction of t
he anti-p81 antiserum into the cytoplasm of RS-4 cells blocked their e
ntry into S phase suggesting that the protein has a proliferative func
tion, Immunostaining of normal mouse tissues showed that the expressio
n of p81/ezrin was highest in proliferating cell populations. Unlike R
S-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.