The Trypanosoma cruzi immunosuppressive factor (TIF) targets a lymphocyte activation event subsequent to increased intracellular calcium ion concentration and translocation of protein kinase C but previous to cyclin D2 and cdk4 mRNA accumulation.
Many immunosuppressive effects of Trypanosoma cruzi can be reproduced in vitro by a preparation consisting of molecules spontaneously released by this protozoan (termed trypanosomal immunosuppressive factor (TIF)). In this work, we attempted to establish whether TIF-induced inhibition of lymphoproliferation results from preventing lymphocyte activation or impairing a post-activation process. Although [3H]thymidine uptake and expression of CD25 by normal human T lymphocytes stimulated with a phorbol ester were markedly reduced by T. cruzi or TIF, translocation of cytosolic protein kinase C (PKC) to the cell membrane was not affected. Lymphoproliferation induced by ionomycin was also inhibited by T. cruzi or TIF but the typical elevation of intracellular calcium ions [Ca2+]i caused by this calcium ionophore was not altered. The increase in [Ca2+]i induced with anti-CD3 antibody was also unaffected by TIF. TIF did not preclude lymphocytes stimulated with phytohemagglutinin from accumulating normal mRNA levels of NFAT1 (also known as NFATp) and NFATc. NFAT1 and NFATc are components of the NFAT complex that controls transcription of genes coding for several cytokines and whose translocation to the nucleus is dependent upon PKC activation and increased [Ca2+]i. In contrast, the mRNA levels of cyclin D2 and cdk4, which form a holoenzyme complex known to regulate cell progression through the G1 phase, were markedly reduced by TIF. These results indicated that TIF did not inhibit lymphocyte activation leading to early secondary signaling but curtailed a mechanism controlling cell progression through G1 and necessary for reaching S phase.
Kierszenbaum
F
F
Department of Microbiology, Michigan State University, East Lansing 48824, USA. kierszen@pilot.msu.edu
Majumder
S
S
Paredes
P
P
Tanner
M K
MK
Sztein
M B
MB
D000818:Animals; D001692:Biological Transport; D017252:CD3 Complex / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D056742:Cyclin D2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases / Q000096:biosynthesis / Q000235:genetics; D016213:Cyclins / Q000096:biosynthesis / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D015759:Ionomycin / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000187:drug effects*; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D011493:Protein Kinase C / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger / Q000096:biosynthesis; D016053:RNA, Protozoan / Q000096:biosynthesis; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014157:Transcription Factors / Q000378:metabolism; D014349:Trypanosoma cruzi / Q000276:immunology*
C080336:CCND2 protein, human; D017252:CD3 Complex; D056742:Cyclin D2; D016213:Cyclins; D004268:DNA-Binding Proteins; D007166:Immunosuppressive Agents; D050778:NFATC Transcription Factors; C494006:NFATC2 protein, human; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D016053:RNA, Protozoan; D011948:Receptors, Antigen, T-Cell; D014157:Transcription Factors; D015759:Ionomycin; D011493:Protein Kinase C; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium