Increase in nuclear calcium concentration has several biological effects which include controlling calcium-activated gene transcription. Using extracellular ATP to induce intracellular calcium transient as a model, Western blotting, immunofluorescence, real-time PCR as well as Ca²⁺ image studies were carried out. It was found that inositol 1, 4, 5-trisphosphate receptors (IP₃Rs) and endoplasmic reticulum protein 44 (ERp44) co-localized on the nuclear envelope and endoplasmic reticulum (ER). Extracellular ATP induced nuclear calcium transient via IP₃Rs and subsequently increased the cAMP response element binding protein (CREB) phosphorylation and the expression of c-Myc. However, all these were inhibited by 2-aminoethoxydiphenyl borate (2-APB), an IP₃Rs inhibitor, and by over-expression of ERp44. These results suggest that ERp44 inhibits gene transcription via IP₃Rs in HeLa cells.