Apoptosis and Bcl-2 expression in cultured murine splenic T cells.
To elucidate the mechanism by which bcl-2 affects apoptosis in post-thymic T cells, we investigated the expression of Bcl-2 protein in primary cultures of splenic T cells and in the interleukin-2 (IL-2)-dependent T-cell line CTLL-2. The overall level of Bcl-2 was determined by immunoblotting, and the variability in Bcl-2 expression was determined by flow cytometry. For a few days after concanavalin A (Con A) plus IL-2 activation, the overall level of Bcl-2 in T cells remains unchanged, but it becomes more heterogeneous. By 5 days after activation, the expression returns to a more homogeneous distribution, but it is increased up to threefold above pre-activation levels, depending upon the dose of IL-2 supplied. When Con A blasts or CTLL-2 cells are deprived of IL-2 for 24 hr, there is no change in their overall Bcl-2 levels which remain homogeneous even though almost half of the cells are apoptotic. However, when bcl-2 transfected CTLL-2 cells are deprived of IL-2, they do not undergo apoptosis, and their endogenous Bcl-2 protein level slowly decreases relative to their total protein. These data document the IL-2-dependent expression of Bcl-2 in activated T cells, confirm the ability of deregulated bcl-2 to inhibit the onset of apoptosis after IL-2 withdrawal, but suggest that, after IL-2 withdrawal, a drop in Bcl-2 levels relative to total protein levels does not precede apoptosis.
Broome
H E
HE
Department of Pathology, University of California, San Diego, La Jolla 92093-0612, USA.
Dargan
C M
CM
Bessent
E F
EF
Krajewski
S
S
Reed
J C
JC
D000818:Animals; D017209:Apoptosis / Q000276:immunology* / Q000502:physiology; D002478:Cells, Cultured; D003208:Concanavalin A / Q000276:immunology; D004306:Dose-Response Relationship, Immunologic; D005434:Flow Cytometry; D007376:Interleukin-2 / Q000276:immunology; D008213:Lymphocyte Activation; D051379:Mice; D008810:Mice, Inbred C57BL; D011518:Proto-Oncogene Proteins / Q000276:immunology* / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2; D013154:Spleen / Q000276:immunology* / Q000378:metabolism; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D014407:Tumor Cells, Cultured
D007376:Interleukin-2; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D003208:Concanavalin A