A lymphoma cell line expressing elevated levels of tyrosine protein kinase activity

The major in vitro substrate for a tyrosine protein kinase in the particular fraction of the lymphoma cell line LSTRA is a protein of approximately 58,000 daltons (pp58). In order to determine if this phosphorylation is unique to the LSTRA cells, the particulate fractions from normal mouse T lymphocytes and another lymphoma cell line, YAC-1, were examined for the presence of pp58 phosphorylation. These two cell types were found to contain this phosphorylation, although in vitro pp58 phosphorylation is elevated approximately 20-40-fold in the LSTRA cells over that found in T lymphocytes or YAC-1 cells. A comparison was also made of the levels of tyrosine protein kinase activity among these three cell types. Tyrosine protein kinase activity was measured in vitro using an exogenously added synthetic peptide substrate and in vivo by determining cellular phosphotyrosine levels. The results of these determinations indicate that the LSTRA cell line contains an elevated level of tyrosine protein kinase activity.