COMPARISON OF P56(LCK) AND P59(FYN) PROTEIN EXPRESSION IN THYMOCYTE SUBSETS, PERIPHERAL T-CELLS, NK CELLS, AND LYMPHOID-CELL LINES

The expression of the src-family kinases, p56(lck) and p59(fyn), is cr itical for thymocyte development and TCR-mediated signal transduction, and may be important for signaling through other lymphoid receptors a s well. Overexpression studies have demonstrated that the levels of p5 6(lck) and p59(fyn) expression can affect T cell development and signa ling through the TCR. Therefore, it is likely that their exact express ion levels play an important role in modulating signaling in thymocyte s, mature T cells, and other lymphocytes. Here, we used quantitative i mmunoblotting to measure p56(lck) and p59(fyn) protein expression leve ls in thymocyte subsets, peripheral T cells, NK cells, and lymphoid ce ll lines, p59(fyn) expression levels were similar to p56(lck) in most cells that were examined demonstrating that p59(fyn) is abundantly exp ressed in T cells. In addition, we found that p56(lck) protein express ion is equivalent in CD4 and CD8 double-negative, double-positive, and single-positive thymocytes. In contrast, p59(fyn) expression levels w ere significantly lower in double-positive thymocytes than in the othe r thymocyte subpopulations. Finally, we demonstrate that p56(lck) and p59(fyn) expression varies greatly in a number of cell lines used to s tudy T cell activation and that IL-2 treatment can dynamically regulat e p56(lck) and p59(fyn) expression in some cells.