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Secretion, Glycosylation, and Phosphorylation of Rat-specific, Transformation-associated Proteins in Moloney Murine Sarcoma Virus-transformed Rat Cells¹

Department of Tumor Biology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030

Previously, we detected, by monoclonal antibody, three Moloney murine sarcoma virus (Mo-MSV)-activated intracellular transformation-associated proteins (TAP), (P66, P63, and P60) in several Mo-MSV-transformed rat cell lines (Chan et al., Biochem. Biophys. Res. Commun., 134: 1223–1230, 1986) and found the release of TAP into the extracellular medium with a change from three intracellular polypeptides to two extracellular polypeptides (P68 and P64) (Li et al., Virology, 156: 91–100, 1987). Since then, we have further analyzed TAP in terms of their secretion, glycosylation, and phosphorylation in a temperature-sensitive Mo-MSV-transformed normal rat kidney (NRK) cell line, the 6M2 line, and found these results. Extracellular TAP were detected by immuno-blotting and immunoprecipitation techniques as two polypeptides (P68 and P64). The secretion of TAP was rapid, with a 50% secretion rate of 78 min. Both intracellular (except for P63) and extracellular TAP were glycosylated. As a result of inhibition of glycosylation by the antibiotic tunicamycin, a fourth intracellular TAP (P58) and a third extracellular TAP (P60) were found. The new results suggest that the intracellular TAP were probably changed from four polypeptides (P66, P63, P60, and P58) to three (P66, P63, and P60) during the glycosylation process. Likewise, the three extracellular TAP were changed to two (P68 and P64) as a result of further glycosylation and subsequent secretion into the extracellular medium. Inhibition of glycosylation by tunicamycin (0.5 µg/ml) reduced the TAP secretion rate by about 39%. Extracellular TAP (P68 and P64) as well as P85^gag-mos and P58^gag were found to be phosphoproteins.

¹ This project was supported by the University Cancer Foundation Grants 175409 and 174391 of The University of Texas M. D. Anderson Cancer Center in Houston, Korea Green Cross Foundation, Grant 170366, and the Council for Tobacco Research—USA, Inc., Grant 2264M.

² To whom requests for reprints should be addressed, at Department of Tumor Biology, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030.

Received 7/13/88. Revised 12/ 7/88. Accepted 1/ 5/89.