Post-translational regulation of the 54K cellular tumor antigen in normal and transformed cells.

Abstract

The 54K cellular tumor antigen has been translated in vitro, using messenger ribonucleic acids from simian virus 40 (SV40)-transformed cells or 3T3 cells. The in vitro 54K product could be immmunoprecipitated with SV40 tumor serum and had a peptide map that was similar, but not identical, to the in vivo product. The levels of this 54K protein in SV3T3 cells were significantly higher than those detected in 3T3 cells (D. I. H. Linzer, W. Maltzmnan, and A. J. Levine, Virology 98:308-318, 1979). In spite of this, the levels of translatable 54K messenger ribonucleic acid from 3T3 and SV3T3 cells were roughly equivalent or often greater in 3T3 cells. Pulse-chase experiments with the 54K protein from 3T3 or SV3T3 cells demonstrated that this protein, once synthesized, was rapidly degraded in 3T3 cells but was extremely stable in SV3T3 cells. Similarily, in an SV40 tsA-transformed cell line, temperature sensitive for the SV40 T-antigen, the 54K protein was rapidly turned over at the nonpermissive temperature and stable at the permissive temperature, whereas the levels of translatable 54K messenger ribonucleic acid at each temperature were roughly equal. These results demonstrate a post-translational regulation of the 54K cellular tumor antigen and suggest that this control is mediated by the SV40 large T-antigen. Animals bearing simian virus 40 (SV40)-induced tumors produce antibody to two viruscoded proteins, the large T-antigen (24) and the small t-antigen (3,20), and a cellular protein of about 54,000 molecular weight (54K) (2,9,10,12,16,23). The 54K protein has been detected in mouse 3T3 cells at about 2% the levels expressed in SV40-transformed 3T3 cells (13). SV40 infection of 3T3 cells results in a 20-to 30-fold increase in the levels of detectable 54K protein in these cells (12, 13). The SV40 A gene product, or large T-antigen, is required for this stimulation in the level of the cellular 54K protein in both virus-infected and -transformed mouse cells (13). Similar or identical proteins of 53,000 to 55,000 molecular weight have been detected in murine chemically transformed cell lines (4), embryonal carcinoma cell lines (12), spontaneously transformed cells (4; W. Maltzman, M. Oren, and A. J. Levine, Virology, in press), and lymphocytes from irradiation-induced leukemia (4). Both immunologically and chemically related 54K proteins have been detected in SV40-transformed rat, hamster, monkey, and human cell lines (6,22). Thus, the expression of high levels of the 54K protein appears to be correlated with btansformation (although not every transformed cell line expresses detectable levels of this protein), and the 54K protein appears to have been conserved, in part, over evolutionary time scales.The mechanism by which the SV40 T-antigen increases the levels of the 54K cellular protein in virus-infected or -transformed cells is at present unclear. The SV40 A gene product might stimulate the de novo synthesis of the 54K protein, as it apparently does for several celllar enzymatic activities (8,19) and the cellular ...

A fluorescent p53GFP fusion protein facilitates its detection in mammalian cells while retaining the properties of wild-type p53

“…In Balb/c 3T3 cells the fusion protein had the same half-life as that of the exogenous human wtp53, and as the endogenous murine wtp53 protein. This result is consistent with the reported half-life of wtp53 in many non-transformed cell types (Mercer and Baserga, 1985;Oren et al, 1981).…”

Sodium butyrate inhibits the synthesis of the transformation related protein p 53 in 3T6 mouse fibroblasts

“…The half-life of p 53 varies dramatically in normal vs transformed cells: 20-60 min in 3T3 cells but longer than 20 h in SV 40 transformed 3T3 cells [26]. In pulse-chase experiments we found a half-life of about 6 h for p 53 in our 3T6 cell line ( fig.3d,e); this is considerably longer than that of the protein in 3T3 cells implying that 3T6 cells in this aspect behave more like transformed ones which is in agreement with other properties of this cell line [9,10,27].…”

Loss of function and p53 protein stabilization

“…Three viral oncoproteins have been reported to inhibit p53 function and increase its levels: (1) Ad E1b, a 55-kD protein, forms a complex with p53, disrupting its trans-activational activity but also leading to its stabilization (Lane and Crawford, 1979; Linzer and Levine, 1979;Oren et al, 1981;Sarnow et al, 1982;Braithwaite and Jenkins, 1989;Yew and Berk, 1992). (2) SV40 large T antigen binds to p53 eliminating wt p53 speci®c functions and stabilizes p53 (Braithwaite and Jenkins, 1989;Farmer et al, 1992).…”

“…However, stabilization is not solely a property of mutant p53 protein, since it can also occur with wild-type p53 following a variety of stimuli, and these can result in either a decrease or an increase in function (Table 1). Thus, p53 elevation following transformation by DNA tumor viruses [SV40 large Tantigen (Oren et al, 1981;Sarnow et al, 1982;Deppert and Haug, 1986), E1B and E1A oncoproteins (Braithwaite and Jenkins, 1989;Yew and Berk, 1992;Steegenga et al, 1996)] results in a loss of p53 function. In contrast, stabilization following pharmacological stimuli, including DNA damage, hypoxia, depletion of ribonucleotide pools, and microtubule disruption, result in a higher level of a functional p53 (Maltzman and Czyzyk, 1984;Kastan et al, 1991Kastan et al, , 1992Fritsche et al, 1993;Graeber et al, 1994;Blagosklonny et al, 1995a;Chernova et al, 1995;Tishler et al, 1995;Wahl et al, 1996;Linke et al, 1996).…”