Attali B, Latter H, Rachamim N, Garty H
Department of Membrane Research and Biophysics, Weizmann Institute of Science, Rehovot, Israel.
Proc Natl Acad Sci U S A. 1995 Jun 20;92(13):6092-6. doi: 10.1073/pnas.92.13.6092.
Screening a rat colon cDNA library for aldosterone-induced genes resulted in the molecular cloning of a cDNA whose corresponding mRNA is strongly induced in the colon by dexamethasone, aldosterone, and a low NaCl diet. A similar mRNA was detected in kidney papilla but not in brain, heart, or skeletal muscle. Xenopus laevis oocytes injected with cRNA synthesized from this clone, designated CHIF (channel-inducing factor), express a K(+)-specific channel activity. The biophysical, pharmacological, and regulatory characteristics of this channel are very similar to those reported before for IsK (minK). These include: slow (tau > 20 s) activation by membrane depolarization with a threshold potential above -50 mV, blockade by clofilium, inhibition by phorbol ester, and activation by 8-bromoadenosine 3',5'-cyclic monophosphate and high cytoplasmic Ca2+. The primary structure of this clone, however, shows no homology to IsK. Instead, CHIF exhibits > 50% similarity to two other short bitopic membrane proteins, phospholemman and the gamma subunit of Na+K(+)-ATPase. The data are consistent with the possibility that CHIF is a member of a family of transmembrane regulators capable of activating endogenous oocyte transport proteins.
通过筛选大鼠结肠cDNA文库寻找醛固酮诱导基因，得到了一个cDNA的分子克隆，其对应的mRNA在结肠中可被地塞米松、醛固酮和低氯化钠饮食强烈诱导。在肾乳头中检测到了类似的mRNA，但在脑、心脏或骨骼肌中未检测到。用从该克隆（命名为CHIF，即通道诱导因子）合成的cRNA注射非洲爪蟾卵母细胞后，可表达一种钾离子特异性通道活性。该通道的生物物理、药理和调节特性与之前报道的IsK（minK）非常相似。这些特性包括：膜去极化时缓慢（时间常数>20秒）激活，阈值电位高于-50 mV，被氯非铵阻断，被佛波酯抑制，以及被8-溴腺苷3',5'-环磷酸和高细胞质钙离子激活。然而，该克隆的一级结构与IsK没有同源性。相反，CHIF与另外两种短的双位膜蛋白——磷膜蛋白和钠钾ATP酶的γ亚基有超过50%的相似性。这些数据与CHIF是能够激活内源性卵母细胞转运蛋白的跨膜调节因子家族成员这一可能性一致。
