Kanzaki M, Nie L, Shibata H, Kojima I
Department of Cell Biology, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi 371, Japan.
J Biol Chem. 1997 Feb 21;272(8):4964-9. doi: 10.1074/jbc.272.8.4964.
CD20 functions as a calcium-permeable cation channel. When expressed in Balb/c 3T3 cells, CD20 accelerates the G1 progression induced by insulin-like growth factor-I (IGF-I). To further characterize how CD20 modulates the action of IGF-I, we investigated whether the activity of CD20 channel was affected by IGF-I. In quiescent cells expressing CD20, IGF-I increased cytoplasmic free calcium concentration, [Ca2+]c, which was reversed by the removal of extracellular calcium. In contrast, IGF-I did not increase [Ca2+]c in cells that did not express CD20. In perforated patch clamp recordings, addition of IGF-I to the bath solution augmented the Ca2+ permeability, which was reversed by anti-CD20 antibody. In cell-attached patch, calcium-permeable channel activity with unitary conductance of 7 picosiemens was detected, which was abolished by anti-CD20 antibody. The single channel activities were markedly enhanced when IGF-I was included in the pipette solution, whereas IGF-I added to the bath solution was ineffective. When cells were first exposed to pertussis toxin, activation of the channel by IGF-I was blocked. Transfection of cDNA for Gip2, a constitutive active form of alphai2, activated the CD20 channel. These results indicate that the CD20 channel is regulated by the IGF-I receptor by a mechanism involving pertussis toxin-sensitive G protein.
CD20作为一种钙通透性阳离子通道发挥作用。当在Balb/c 3T3细胞中表达时，CD20可加速胰岛素样生长因子-I（IGF-I）诱导的G1期进程。为了进一步阐明CD20如何调节IGF-I的作用，我们研究了IGF-I是否会影响CD20通道的活性。在表达CD20的静止细胞中，IGF-I增加了细胞质游离钙浓度[Ca2+]c，去除细胞外钙可使其逆转。相比之下，IGF-I在不表达CD20的细胞中不会增加[Ca2+]c。在穿孔膜片钳记录中，向浴液中添加IGF-I可增强Ca2+通透性，抗CD20抗体可使其逆转。在细胞贴附式膜片中，检测到了单位电导为7皮西门子的钙通透性通道活性，抗CD20抗体可将其消除。当移液管溶液中含有IGF-I时，单通道活性显著增强，而添加到浴液中的IGF-I则无效。当细胞首先暴露于百日咳毒素时，IGF-I对通道的激活被阻断。转染组成型活性形式的αi2（Gip2）的cDNA可激活CD20通道。这些结果表明，CD20通道受IGF-I受体调节，其机制涉及百日咳毒素敏感的G蛋白。
