Role of Nuclear Chromogranin B in Inositol 1,4,5-Trisphosphate-Mediated Nuclear Ca²⁺ Mobilization

Abstract

Recently, secretory granule Ca(2+) storage protein chromogranin B (CGB) was shown to be present in the nucleoplasm proper in a complex structure that consists of the inositol 1,4,5-trisphosphate receptor (IP(3)R)/Ca(2+) channels and the phospholipids. Further, the amounts of IP(3)Rs present in the nucleus of bovine chromaffin cells were shown to be comparable to that of the endoplasmic reticulum. Therefore, we investigated here the potential contribution of nuclear CGB on the IP(3)-dependent Ca(2+) mobilization in the nucleus, using both neuroendocrine PC12 and nonneuroendocrine NIH3T3 cells. Chromogranin A (CGA) expression in the NIH3T3 cells, which do not contain intrinsic chromogranins, increased the IP(3)-induced Ca(2+) releases in the nucleus by 45%, while CGB expression in the same cells increased the IP(3)-induced Ca(2+) releases in the nucleus by 80%. Microinjection of IP(3) into the nucleus of CGB-expressing NIH3T3 cells increased the IP(3)-dependent nuclear Ca(2+) mobilization approximately 3-fold, whereas in CGA-expressing cells it remained the same as that of control cells. In contrast, inhibition of CGA expression in PC12 cells by siRNA treatment decreased the IP(3)-induced Ca(2+) releases in the nucleus by 17%, while inhibition of CGB expression decreased the IP(3)-induced Ca(2+) releases in the nucleus by 55%. Microinjection of IP(3) into the nucleus of siCGB-treated PC12 cells decreased the IP(3)-dependent nuclear Ca(2+) mobilization by approximately 75%, whereas in siCGA-treated cells it remained the same as that of control cells. Given the presence of CGB in the nucleus, these results further highlight the critical contribution of nuclear CGB in the IP(3)-induced Ca(2+) release in the nucleus.

Inositol Trisphosphate Receptor Ca2+Release Channels

“…Interference of the interaction between chromogranins and InsP 3 R with an expressed chromogranin peptide targeted to the ER lumen in neuronally differentiated PC12 cells, inhibited Ca 2ϩ release response to the muscarinic agonist carbachol (87). CGB is also found in the nucleus in a complex with phospholipids and the InsP 3 R, and it has been suggested that the interaction could modulate InsP 3 -dependent Ca 2ϩ signaling within the nucleoplasm (194).…”

C-terminal Domain of Chromogranin B Regulates Intracellular Calcium Signaling

“…1A) were constructed as described under "Experimental Procedures." Full-length CGB and its fragments were expressed in NIH3T3 cells, a mouse fibroblast cell line without endogenous CGB (10). Expression and localization were determined via Western blotting (Fig.…”

Secretory granules in inositol 1,4,5‐trisphosphate‐dependent Ca2+signaling in the cytoplasm of neuroendocrine cells

“…In view of the presence of the majority of cellular calcium, IP 3 R/Ca 2+ channels, and chromogranins in secretory granules, which is necessary for an organelle to function as the major IP 3 ‐sensitive intracellular Ca 2+ store, it would be natural for secretory granules to play the most significant role in the IP 3 ‐dependent intracellular Ca 2+ control mechanism. Whether secretory granules play the major role in the cytoplasmic IP 3 ‐dependent Ca 2+ control mechanism could be discerned by comparing the magnitudes of the IP 3 ‐mediated Ca 2+ releases between the cells that contain different numbers of secretory granules (27, 83).…”

“…Given that only the number of secretory granules formed is reduced in the cytoplasm, these results indicate that secretory granules are responsible for the majority of IP 3 ‐mediated cellular Ca 2+ release in the cytoplasm of neuroendocrine PC12 cells (27). On the other hand, induction of secretory granule formation by expressing chromogranins in nonneuroendocrine NIH3T3 cells that normally do not contain any secretory granules markedly increased the magnitude of IP 3 ‐induced Ca 2+ release of these cells (27, 83). When secretory granule formation was induced by expressing CGA in NIH3T3 cells, the magnitude of IP 3 ‐induced Ca 2+ release in the cytoplasm of NIH3T3 cells increased ~2.7‐fold over the control (Fig.…”