A src-related 120,000-dalton protein expressed in an avian sarcoma virus-transformed rat cell line

Phosphotyrosine-containing 120,000-dalton protein coimmunoprecipitated with pp60v-src from Rous sarcoma virus-transformed mammalian cells

Serum from rabbits bearing tumors (TBR serum) induced by the Rous sarcoma virus (RSV) was originally developed to identify the RSV src gene protein-pp60v-src. It is also capable of directly or indirectly immunoprecipitating a number of proteins besides pp60v-src from lysates of RSV-transformed cells. This report describes a highly phosphorylated protein of approximately 120,000 Da (pp120) which is specifically immunoprecipitated from RSV-transformed mammalian cells by TBR sera and monospecific antibodies against pp60v-src. However, it was not immunoprecipitated by TBR serum from RSV-transformed chicken embryo fibroblasts. Phosphoamino acid analysis revealed that pp120 contains phosphoserine and phosphotyrosine in relative amounts similar to that found in pp60v-src. Various experimental results indicate that pp120 is not structurally related to RSV virion proteins or to the putative pp60v-src substrate-vinculin. Furthermore, proteolytic peptide mapping and immunoblotting experiments indicate that although pp120 is immunoprecipitated by various anti-pp60v-src antibodies, it does not appear to be related to the RSV transforming protein. These results suggest that pp120 is distinct from previously reported substrates of pp60v-src and may exist in association with the transforming protein in mammalian cell lysates.

MC29 virus-coded protein occurs as monomers and dimers in transformed cells

The MC29 virus-coded protein p110gag-myc was found exclusively in the nucleus of transformed Japanese quail (Q8) cells, and time course experiments indicated that the protein had a half-life of about 30 min. When extracts of either Q8 or chicken embryo cells infected with MC29 virus were prepared with nondenaturing detergents and then sedimented in sucrose gradients, p110 was found in the fractions expected to contain monomers (5.9S), dimers (9.3S), or mixtures of the two. The same extracts treated with denaturing detergent (0.2% sodium dodecyl sulfate) exhibited p110 only in fractions expected for the monomeric protein, but beta-mercaptoethanol had no effect on the original distribution. Gradients prepared with 0.5 or 1.0 M NaCl failed to dissociate the faster-sedimenting form. No other protein or polyribonucleotide which could increase the sedimentation rate of p110 was found, and neither RNase nor DNase altered the sedimentation pattern of p110 in nondenatured extracts. A reassociation of monomeric p110 into dimers discernible by gel electrophoresis was demonstrated.

Correlation between tumor-specific surface antigens and src gene expression in Rous sarcoma virus-induced rat tumors

Immunization with Rous sarcoma virus (RSV)-induced mouse tumors or with SR-3Y1 or NY8-3Y1 rat fibroblasts transformed by a wild type RSV or an env gene deletion mutant of RSV induced complete transplantation resistance against an RSV-induced mouse tumor (CSA1M) in syngeneic hosts. On the other hand, 10 of 19 mice immunized with ts68-3Y1 rat fibroblasts transformed by an src gene temperature-sensitive mutant of RSV (permissive temperature: 33-35 degrees C) could not reject the CSA1M. SR-3Y1, NY8-3Y1 and RSV-induced mouse tumors expressed a common tumor-specific cell-surface antigen (TSSA) detected by a syngeneic rat antiserum against NY8-3Y1. In ts68-3Y1, expression of the TSSA was temperature-sensitive, TSSA being detected only when ts68-3Y1 was cultivated at the permissive temperature. Immunoprecipitation showed that serum from a rabbit bearing an RSV-induced tumor detected a 60-kdalton protein in cell extracts from SR-3Y1 and NY8-3Y1. Antiserum to NY8-3Y1 failed to detect this protein. These results suggest that the tumor-specific surface antigen(s) on RSV-induced mammalian tumors was coded for by an RSV src gene that was not identical with the simple form of the 60-kdalton protein identified.