Expression of calcium-permeable cation channel CD20 accelerates progression through the G1 phase in Balb/c 3T3 cells.
CD20 is a transmembrane protein that functions as a Ca(2+)-permeable cation channel (Bubien, J. K., Zhou, L. J., Bell, P. D., Frizzel, R. A., and Tedder, T. F. (1993) J. Cell Biol. 121, 1121-1132) and is involved in growth regulation of B lymphocytes. In order to further investigate the role of calcium entry in cell cycle progression, we introduced the cDNA encoding a Ca(2+)-permeable cation channel, CD20, into Balb/c 3T3 cells. Balb/c 3T3 cells transfected with a vector containing cDNA encoding CD20 expressed the CD20 protein, which was detected by assaying the binding of a monoclonal antibody against CD20. Calcium-permeable cation channel activity was detected in CD20-expressing cells by whole cell patch clamp recording and microfluorometric determination of the cytoplasmic Ca2+ concentration using fura-2. The expression of CD20 induced significant alterations in the responses of the cells to insulin-like growth factor-I (IGF-I). IGF-I induced DNA synthesis by control cells only when they had been pretreated with both platelet-derived growth factor (PDGF) and epidermal growth factor (EGF). In contrast, DNA synthesis by 30% of the quiescent CD20-expressing cells was initiated in response to IGF-I in the absence of priming with PDGF and EGF. When control quiescent cells were primed with PDGF and EGF, the addition of IGF-I led to the initiation of DNA synthesis after 14 h or more, whereas it induced DNA synthesis by CD20-expressing cells primed with PDGF and EGF 4 h earlier. The IGF-induced DNA synthesis was dependent on extracellular Ca2+, and expression of CD20 reduced the concentration of extracellular Ca2+ required for it. Furthermore, DNA synthesis by approximately 25% of the CD20-expressing cells was initiated after priming with PDGF and EGF, even in the absence of the progression factor IGF-I. These results indicate that CD20 expressed in Balb/c 3T3 cells functions as a constitutively active Ca(2+)-permeable cation channel and that expression of CD20 accelerates G1 progression in a Ca(2+)-dependent manner.
Kanzaki
M
M
Department of Cell Biology, Gunma University, Maebashi, Japan.
Shibata
H
H
Mogami
H
H
Kojima
I
I
D016475:3T3 Cells; D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000502:physiology*; D018951:Antigens, CD20; D000944:Antigens, Differentiation, B-Lymphocyte / Q000235:genetics / Q000502:physiology*; D001483:Base Sequence; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000235:genetics / Q000502:physiology*; D002412:Cations; D017931:DNA Primers; D004261:DNA Replication / Q000235:genetics; D018076:DNA, Complementary; D016193:G1 Phase / Q000235:genetics / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D010766:Phosphorylation; D014162:Transfection
D015703:Antigens, CD; D018951:Antigens, CD20; D000944:Antigens, Differentiation, B-Lymphocyte; D015220:Calcium Channels; D002412:Cations; D017931:DNA Primers; D018076:DNA, Complementary; D007334:Insulin-Like Growth Factor I; D002118:Calcium