Pluse-Labeling studies of tumor-antigen TA-4 in squamous cell carcinoma cells

A tumor antigen TA-4 of squamous cell carcinoma can be devided into two subgroups (acidic TA-4 with pI of less than 6.25 and neutral TA-4 with pI of 6.25 or greater) by isoelectric focusing method (IFF), and acidic TA-4 is particularly relating to the malignant cells. The present study demonstrates the production of acidic TA-4 by in vitro cell line system. SKG III a cells, an established cell line of squamous cell carcinoma, were labeled with ^3H-labeled leucine for 3 minutes, and IFF patterns of radiolabeled TA-4 subfractions were chased at different intervals of time after the label. Immediately after the label, the radioactivity appeared only in acidic TA-4, which remains for up to 2 hours and disappeared 24 hours after the label. Small amount of radiolabeled neutral TA-4 was produced when the cells were incubated with ^3H-leucine for 24 hours. The cells were also incubated with several radiolabeled sugar, including ^3H-mannose, ^3H-glucosamie, or ^3H-galactose, for 24 hours, resulting in the incorpolation of the radioactivity into acidic TA-4. These results indicated that acidic TA-4 was synthesized in a different manner from neutral TA-4, and that acidic TA-4 contained some sugar chains.