Comparison of signaling pathways involved in apoptosis of a thymocyte hybridoma triggered by a rat thymic medullary epithelial cell line, dexamethasone or T-cell receptor cross-linking.
Using an in vitro co-culture assay we found that a rat medullary thymic epithelial cell (TEC) line (TE-R2.5) induces apoptosis of the BWRT8 thymocyte hybridoma (TH) (CD4(hi)CD8(low) alphabetaTCR(hi)). TH apoptosis induced by this TEC line was predominantly mediated by direct cell-cell contacts and was potentiated by cross-linking of the T cell receptor (TCR) by R73 monoclonal antibody (mAb). Dexamethasone (Dx) also triggered TH apoptosis but inhibited death of these cells induced by TE-R2.5 cells or immobilized R73 mAb. The TEC-induced apoptosis was independent of the LFA-1/ICAM-1 interaction but partly depended on a novel 29 kDa molecule expressed on TE-R2.5 cells. All three types of TH apoptosis were followed by the cleavage of poly-(ADP-ribose)-polymerase and were blocked by a caspase inhibitor Z-Val-Ala-Asp(OMe)-CH(2)F.PKC stimulation by phorbol myristate acetate interfered with the TH apoptosis induced by TE-R2.5 and Dx, but did not modulate the effect of R73 mAb. On the contrary, inhibition of calcineurin with cyclosporine A did not influence the apoptosis induced by TE-R2.5 and Dx, but completely prevented the R73-triggered TH cell death. The TE-R2.5-mediated BWRT8 apoptosis was suppressed by Na-orthovanadate, an inhibitor of protein tyrosine phosphatases (PTP) as well as by genistein, a protein tyrosine kinase (PTK) inhibitor, while both compounds potentiated the effect of Dx. Blocking PTP, but not PTK decreased the proapoptotic effect of R73 mAb. These results, including those using a BWRT8 subclone (BWRT8-MDP.2) which is resistant to TCR-triggered apoptosis, but sensitive to apoptosis stimulated by TE-R2.5 and Dx, indicate that TE-R2.5-induced TH apoptosis in our model is different from apoptosis in other TEC co-culture models, published so far.
Popović
P
P
Institue of Medical Research, Military Medical Academy, Crnotravska 17, 11002, Belgrade, Yugoslavia.
Colić
M
M
Vucević
D
D
Gasić
S
S
Pavicić
L
L
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000276:immunology*; D020169:Caspases / Q000502:physiology; D002450:Cell Communication / Q000276:immunology; D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology*; D004847:Epithelial Cells / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology / Q000276:immunology; D006825:Hybridomas / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology / Q000276:immunology; D051379:Mice; D051381:Rats; D011948:Receptors, Antigen, T-Cell / Q000276:immunology* / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology / Q000276:immunology; D014407:Tumor Cells, Cultured
D011948:Receptors, Antigen, T-Cell; D003907:Dexamethasone; D020169:Caspases