Transfection of the CD20 cell surface molecule into ectopic cell types generates a Ca2+ conductance found constitutively in B lymphocytes.
CD20 is a plasma membrane phosphoprotein expressed exclusively by B lymphocytes. mAb binding to CD20 alters cell cycle progression and differentiation, indicating that CD20 plays an essential role in B lymphocyte function. Whole-cell patch clamp and fluorescence microscopy measurements of plasma membrane ionic conductance and cytosolic-free Ca2+ activity, respectively, were used to directly examine CD20 function. Transfection of human T and mouse pre-B lymphoblastoid cell lines with CD20 cDNA and subsequent stable expression of CD20 specifically increased transmembrane Ca2+ conductance. Transfection of CD20 cDNA and subsequent expression of CD20 in nonlymphoid cells (human K562 erythroleukemia cells and mouse NIH-3T3 fibroblasts) also induced the expression of an identical transmembrane Ca2+ conductance. The binding of a CD20-specific mAb to CD20+ lymphoblastoid cells also enhanced the transmembrane Ca2+ conductance. The mAb-enhanced Ca2+ currents had the same conductance characteristics as the CD20-associated Ca2+ currents in CD20 cDNA-transfected cells. C20 is structurally similar to several ion channels; each CD20 monomer possesses four membrane spanning domains, and both the amino and carboxy termini reside within the cytoplasm. Biochemical cross-linking of cell-surface molecules with subsequent immunoprecipitation analysis of CD20 suggests that CD20 may be present as a multimeric oligomer within the membrane, as occurs with several known membrane channels. Taken together, these findings indicate that CD20 directly regulates transmembrane Ca2+ conductance in B lymphocytes, and suggest that multimeric complexes of CD20 may form Ca2+ conductive ion channels in the plasma membrane of B lymphoid cells.
Bubien
J K
JK
Department of Medicine, University of Alabama, Birmingham 35294.
Zhou
L J
LJ
Bell
P D
PD
Frizzell
R A
RA
Tedder
T F
TF
D000911:Antibodies, Monoclonal; D015703:Antigens, CD / Q000737:chemistry / Q000502:physiology*; D018951:Antigens, CD20; D000944:Antigens, Differentiation, B-Lymphocyte / Q000737:chemistry / Q000502:physiology*; D001402:B-Lymphocytes / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002453:Cell Cycle; D003600:Cytosol / Q000378:metabolism; D004553:Electric Conductivity; D006801:Humans; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D008213:Lymphocyte Activation; D046911:Macromolecular Substances; D010766:Phosphorylation; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D018951:Antigens, CD20; D000944:Antigens, Differentiation, B-Lymphocyte; D046911:Macromolecular Substances; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium