Regulation of intracellular calcium signaling by polycystin 1 expression.

摘要

Polycystic kidney disease (ADPKD) is a genetic disease with the highest occurrence worldwide. Despite its slow progression, this disease still eventually causes kidney failure. It is known that mutations in polycystin-1 (PC1) and/or polycystin-2 (PC2) cause ADPKD. However, the molecular mechanism of how mutations in PC1 and PC2 cause ADPKD is still not known yet. Much of the reason is because the exact function of these proteins is still not known yet.;PC1 is a big protein, and its function is still not clear. PC2 has been suggested as an intracellular Ca2+ channel, residing in the ER. Interference of intracellular Ca2+ homeostasis has been linked to ADPKD phenotypes, and mutations in either PC1 or PC2 cause the same phenotypes. Therefore, we hypothesized that PC1 is also involved in the regulation of Ca2+ signaling.;We expressed the C-terminus tail of PC1 in Xenopus oocytes to directly measure IP3-induced Ca2+ release. We choose oocytes system because we can directly stimulate activation of IP3R by injection of caged IP3 that can be activated through UV photolysis. This system eliminates any confounding factors such as difference in production of IP3. We observed that expression of PC1 fragment results in reduced Ca2 release through IP3R. We further found that the PC1 fragment interacts with ligand-binding domain of IP3R and this binding could perhaps interfere the binding of IP3 to IP3R.;Following up on this observation, we tried to investigate the molecular mechanism of PC1's inhibition on intracellular Ca2+ release and how PC1 regulates intracellular Ca2+ signaling, especially when PC2 is also expressed. Our result suggests that PC1 regulates intracellular Ca2+ release through activation of the PI3K signaling pathway. This pathway regulates the interaction of PC2 with IP3R in the ER. We also found that the interaction between PC2 and IP3R is competitive to the STIM1 and IP3R complex. STIM1 is an ER luminal Ca 2+ level sensor. Reduction in the PC2-IP3R interaction and augmentation of the STIM1-IP3R association inhibits ER Ca 2+ release. In summary, we have shown how PC1 modulates PC2 and STIM1's interaction with IP3R in the ER to regulate intracellular Ca 2+ homeostasis.