Regulation of L-selectin mRNA in Jurkat cells. Opposing influences of calcium- and protein kinase C-dependent signaling pathways.
L-Selectin initiates leukocyte attachment to venular endothelium during lymphocyte recirculation through lymph nodes, leukocyte recruitment into sites of inflammation, and the hematogenous spread of lymphoid malignancies. The density of L-selectin at the cell surface is a major determinant of binding activity and entry into tissues. Post-transcriptional shedding is one control mechanism; however, the extent and physiologic relevance of pre-translational regulation has not been defined. The current study shows that mitogen-/IL-2-driven proliferation of human T cells first increased then markedly decreased the expression of L-selectin on the blast population. The prevalence of specific mRNA showed parallel changes, implying that receptor density is controlled, in part, at the pretranslational level. We used the IL-2-independent Jurkat cell line to determine whether signaling through C-type protein kinases and intracellular calcium regulated L-selectin mRNA directly. Selective pharmacologic activation of these pathways with phorbol esters and calcium ionophore, respectively, resulted in opposite effects on both L-selectin density and mRNA levels. Phorbol esters induced receptor shedding followed by progressive increases in L-selectin density and steady state levels of mRNA. Addition of a calcium ionophore with the phorbol ester blocked both the reexpression of surface receptor and the increase in mRNA. Treatment with ionophore alone resulted in a steady decline in L-selectin expression and mRNA levels. Cyclosporin A, a specific inhibitor of calcineurin, blocked the impact of ionophore on both basal and phorbol-induced levels of L-selectin mRNA. Ionophore alone did not induce apoptosis, significantly alter cell cycle kinetics, or increase transcription of the IL-2 gene under conditions that suppressed L-selectin. Thus, calcineurin seems to be a proximal enzyme in a novel regulatory cascade that suppresses L-selectin expression independent of its known effects on proliferating T cells. In light of the findings in Jurkat, we propose that the protein kinase pathway up-regulates L-selectin mRNA and surface expression early in mitogen-driven T cell proliferation. Chronic elevation of intracellular calcium in repeatedly stimulated T cells then down-regulates expression at the pretranslational level through prolonged activation of calcineurin.
Kaldjian
E P
EP
University of Michigan Medical School, Department of Pathology Medical Sciences, Ann Arbor 48109, USA.
Stoolman
L M
LM
D015152:Blotting, Northern; D002118:Calcium / Q000037:antagonists & inhibitors / Q000502:physiology*; D015815:Cell Adhesion Molecules / Q000096:biosynthesis*; D003208:Concanavalin A / Q000494:pharmacology; D016572:Cyclosporine / Q000494:pharmacology; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000276:immunology*; D006801:Humans; D015759:Ionomycin / Q000494:pharmacology; D019041:L-Selectin; D008213:Lymphocyte Activation / Q000276:immunology; D011493:Protein Kinase C / Q000819:agonists / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis; D015398:Signal Transduction / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D015815:Cell Adhesion Molecules; D012333:RNA, Messenger; D003208:Concanavalin A; D019041:L-Selectin; D015759:Ionomycin; D016572:Cyclosporine; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium