Abstract 1918 P122 Protein, a Positive Regulator for Phospholipase C-σ1, Is Upregulated and Involved in Enhanced Calcium Signaling in Human Coronary Spasm

Abstract

We previously showed that the activity of phospholipase C (PLC)-σ1, a key enzyme for Ca 2+ signaling in the coronary artery smooth muscle, was enhanced threefold in patients with coronary spastic angina (CSA) compared with control subjects. Structural mutation of PLC-σ1 (864G-A) variant with the amino acid replacement of arginine 257 by histidine is one mechanism for the enhanced PLC-σ1 activity, but this was observed in only 10% of CSA patients. PLC-σ1 was shown to be positively regulated by p122 protein. We examined the possible role of p122 protein in the mechanism for enhanced PLC-σ1 activity. In 11 patients with CSA and 9 control subjects without CSA, skin fibroblasts were obtained at the coronary angiography and were cultured. Protein and gene expressions of p122 were determined by Western blot analysis and real-time quantitative RT-PCR, respectively. The protein expression of p122 was enhanced in CSA threefold compared with control subjects (237±17 vs 85±13 units, p<0.0001). The gene expression of p122 was also enhanced in CSA by 36.1±8.7% compared with control (p<0.01). We further examined whether the upregulated p122 protein is associated with the enhancement of intracellular Ca 2+ signaling. Human embryonic kidney cells (HEK293) were cultured and transfected by muscarine M1 receptor. In the cells expressing normal PLC-σ1, acethylcholine (ACh) at 10 −6 and 10 −5 mol/L caused a dose-dependent, rapid transient increase in [Ca 2+ ] i followed by a lower but sustained phase of the increase. We further transfected the HEK293 cells by p122, which resulted in the increased expression of p122 protein two-to threefold. [Ca 2+ ] i at baseline was 23±1 nmol/L in the cells without p122 transfection and 39±2 nmol/L in those with p122 (P<0.01). The peak increase in [Ca 2+ ] i from the baseline after ACh was significantly greater in the cells transfected with p122 than in those without transfection (68±6 versus 33±4 nmol/L at 10 −6 mol/L Ach, and 128±11 versus 67±8 nmol/L at 10 −5 mol/L ACh, both P<0.01). The sustained phase of [Ca 2+ ] i increase was prolonged in the cells with p122 transfection compared with those without transfection. In conclusion, the enhanced p122 protein expression is involved in the pathogenesis of CSA by enhancing intracellular Ca 2+ signaling.