pp60c-src expression is induced by activation of normal human T lymphocytes.
We have re-examined whether pp60c-src, the normal cellular homologue of the transforming protein of Rous sarcoma virus, is present in human T cells. By in vitro immune-complex kinase assay or Western blotting with the anti-pp60c-src mAbs 327 or GD11, pp60c-src was found to be present in lysates of T cell lines, including the Jurkat T cell line. The 327 and GD11 mAbs have been reported to be specific for pp60c-src and not to cross-react with other src family members or other kinases. Furthermore, the size of the pp60c-src bands present on Western blotting and in vitro kinase assay were clearly different from those of p56lck or p59fyn. In addition, pp60c-src is detected in the HTLV-I-derived T cell lines S1T and C8, which lack expression of p56lck and p59fyn. RNase protection assays confirmed that pp60c-src mRNA is present in Jurkat T cells. We also found pp60c-src protein to be constitutively present in freshly isolated thymocytes. In contrast, pp60c-src was absent, or present at extremely low levels, in normal, resting peripheral blood T lymphocytes, which is in agreement with previous findings. However, after stimulation of resting T cells with the mitogenic lectin PHA or with Ab to the TCR complex, pp60c-src expression is induced in both CD4+ and CD8+ T cell subsets, with peak expression detectable 12 to 24 h after T cell activation. The levels of pp60c-src are low in all T cells except Jurkat, where levels of pp60c-src are comparable to levels found in a glioblastoma cell line (T98G). Nevertheless, significant levels of pp60c-src kinase activity are readily detectable in thymocytes and activated normal T cells as well as in T cell lines. The finding that pp60c-src is inducible following activation through the TCR suggests that pp60c-src may play a specific role in the normal T cell activation pathway.
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Research Section, Canadian Red Cross Society, Toronto, Ontario.
Mills
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D015152:Blotting, Northern; D015153:Blotting, Western; D015496:CD4-Positive T-Lymphocytes / Q000201:enzymology; D018414:CD8-Positive T-Lymphocytes / Q000201:enzymology; D004790:Enzyme Induction; D015870:Gene Expression; D006801:Humans; D066298:In Vitro Techniques; D008213:Lymphocyte Activation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051076:Proto-Oncogene Proteins c-fyn; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D016176:T-Lymphocyte Subsets / Q000201:enzymology*
D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D011505:Protein-Tyrosine Kinases; C494957:FYN protein, human; D051076:Proto-Oncogene Proteins c-fyn; D016392:Proto-Oncogene Proteins pp60(c-src)