Non-voltage-gated L-type Ca2+ channels in human T cells: pharmacology and molecular characterization of the major alpha pore-forming and auxiliary beta-subunits.
In T lymphocytes, engagement of the antigen receptor leads to a biphasic Ca2+ flux consisting of a mobilization of Ca2+ from intracellular stores followed by a lower but sustained elevation that is dependent on extracellular Ca2+. The prolonged Ca2+ flux is required for activation of transcription factors and for subsequent activation of the T cell. Ca2+ influx requires as yet unidentified Ca2+ channels, which potentially play a role in T cell activation. Here we present evidence that human T cells express a non-voltage-gated Ca2+ channel related to L-type voltage-gated Ca2+ channels. Drugs that block classical L-type channels inhibited the initial phase of the antigen receptor-induced Ca2+ flux and could also inhibit the sustained phase of the Ca2+ signal suggesting a role for the L-type Ca2+ channel in antigen receptor signaling. T cells expressed transcripts for the alpha(1) 1.2 and alpha(1) 1.3 pore-forming subunits of L-type voltage-gated Ca2+ channels and transcripts for all four known beta-subunits including several potential new splice variants. Jurkat T leukemia cells expressed a small amount of full-length alpha(1)1.2 protein but the dominant form was a truncated protein identical in size to a truncated alpha(1) 1.2 protein known to be expressed in B lymphocytes. They further expressed a truncated form of the alpha(1) 1.3 subunit and auxiliary beta1- and beta3-subunit proteins. Our data strongly suggest that functional but non-voltage-gated L-type Ca2+ channels are expressed at the plasma membrane in T cells and play a role in the antigen receptor-mediated Ca2+ flux in these cells.
Medical Research Council Centre for Immune Regulation, Institute of Biomedical Research, University of Birmingham, Birmingham B15 2TT, United Kingdom.
Leanne
L
Stokes
John
J
Gordon
Gillian
G
Grafton
D017398:Alternative Splicing; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000737:chemistry*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D002469:Cell Separation; D017931:DNA Primers / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D005434:Flow Cytometry; D006801:Humans; D015151:Immunoblotting; D019169:Jurkat Cells; D009447:Neuroblastoma / Q000378:metabolism; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology; D013997:Time Factors; D014158:Transcription, Genetic
C485995:Cacna1d protein, mouse; D020746:Calcium Channels, L-Type; D017931:DNA Primers; C419385:L-type calcium channel alpha(1C); D012333:RNA, Messenger; D012313:RNA; D019284:Thapsigargin; D002118:Calcium