Protein tyrosine phosphatase 1B is a mediator of cyclic ADP ribose-induced Ca2+ signaling in ventricular myocytes.

Cyclic ADP-ribose (cADPR) releases Ca2+ from ryanodine receptor (RyR)-sensitive calcium pools in various cell types. In cardiac myocytes, the physiological levels of cADPR transiently increase the amplitude and frequency of Ca2+ (that is, a rapid increase and decrease of calcium within one second) during the cardiac action potential. In this study, we demonstrated that cADPR levels higher than physiological levels induce a slow and gradual increase in the resting intracellular Ca2+ ([Ca2+]i) level over 10 min by inhibiting the sarcoendoplasmic reticulum Ca2+ ATPase (SERCA). Higher cADPR levels mediate the tyrosine-dephosphorylation of α-actin by protein tyrosine phosphatase 1B (PTP1B) present in the endoplasmic reticulum. The tyrosine dephosphorylation of α-actin dissociates phospholamban, the key regulator of SERCA, from α-actin and results in SERCA inhibition. The disruption of the integrity of α-actin by cytochalasin B and the inhibition of α-actin tyrosine dephosphorylation by a PTP1B inhibitor block cADPR-mediated Ca2+ increase. Our results suggest that levels of cADPR that are relatively higher than normal physiological levels modify calcium homeostasis through the dephosphorylation of α-actin by PTB1B and the subsequent inhibition of SERCA in cardiac myocytes.

Basic fibroblast growth factor increases intracellular magnesium concentration through the specific signaling pathways.

Basic fibroblast growth factor (bFGF) plays an important role in angiogenesis. However, the underlying mechanisms are not clear. Mg(2+) is the most abundant intracellular divalent cation in the body and plays critical roles in many cell functions. We investigated the effect of bFGF on the intracellular Mg(2+) concentration ([Mg(2+)](i)) in human umbilical vein endothelial cells (HUVECs). bFGF increased [Mg(2+)](i) in a dose-dependent manner, independent of extracellular Mg(2+). This bFGF-induced [Mg(2+)](i) increase was blocked by tyrosine kinase inhibitors (tyrphostin A-23 and genistein), phosphatidylinositol 3-kinase (PI3K) inhibitors (wortmannin and LY294002) and a phospholipase Cgamma (PLCgamma) inhibitor (U73122). In contrast, mitogen-activated protein kinase inhibitors (SB202190 and PD98059) did not affect the bFGF-induced [Mg(2+)](i) increase. These results suggest that bFGF increases the [Mg(2+)](i) from the intracellular Mg(2+) stores through the tyrosine kinase/PI3K/PLCgamma-dependent signaling pathways.

[VEGF165-induced angiogenesis by regulating intracellular free Mg2+ in HUVECs].

AIM: The mechanism of vascular endothelial growth factor165 (VEGF165) on intracellular free magnesium ([Mg2+]i) in human umbilical vein endothelial cells (HUVECs) was investigated. METHODS: [Mg2+]i in HUVECs loaded with fluorescent magnesium indicator mag-fura-2 were quantitatively detected the use of intracellular cation measurement system. RESULTS: VEGF165 significantly increased [Mg2+]i in the extracellular Mg2+ and this effect could be blocked by pretreatment with tyrosine kinase inhibitors (tyrphostin A23 and genistein), phosphatidylinositol 3-kinase (PI3K) inhibitors (wortmannin and LY294002) and phospholipase Cgamma (PLCgamma) inhibitor (U73122). In contrast, phospholipase Cgamma (PLCgamma) inhibitor analog (U73343), mitogen-activated protein kinase inhibitors (SB202190 and PD98059) had no effect on the VEGF165-induced [Mg2+]i increase. CONCLUSION: The increase of [Mg2+]i by VEGF165 originates from intracellular Mg2+ pool through tyrosine kinase/ PI3K/PLCgamma-dependent signaling pathways.

[Evidence for a major role of Mg2+ in VEGF165-mediated angiogenesis].

OBJECTIVE: The effect of vascular endothelial growth factor(165) (VEGF(165)) on intracellular free magnesium ([Mg(2+)](i)) and the relationship between Mg(2+) and angiogenesis in human umbilical vein endothelial cells (HUVECs) were investigated in this study. METHODS: [Mg(2+)](i) in HUVECs loaded with fluorescent magnesium indicator mag-fura-2 were quantitatively detected with the use of intracellular cation measurement system. HUVECs were obtained from normal fetus and cultured in M199 with 0.2 fetal bovine serum. The angiogenesis effects of VEGF(165) were observed in presence of 0 mmol/L, 1 mmol/L or 2 mmol/L of extracellular Mg(2+). RESULTS: VEGF(165) significantly increased [Mg(2+)](i) in a dose-dependent manner independent of extracellular Mg(2+), Na(+) and Ca(2+) and this effect could be blocked by pretreatment with VEGF(165) receptor-2 (KDR) inhibitor (SU1498). The angiogenesis induced by VEGF(165) was significantly inhibited cells with 0 mmol/L extracellular Mg(2+), the angiogenesis effects of VEGF(165) were similar in cells with 1 mmol/L and 2 mmol/L extracellular Mg(2+) and these effects could be blocked by SU1498. CONCLUSIONS: These results suggest that the [Mg(2+)](i) increase induced by VEGF(165) originates from intracellular Mg(2+) pools and promotes angiogenesis via KDR-dependent signaling pathways.

Vascular endothelial growth factor increases the intracellular magnesium.

Vascular endothelial growth factor (VEGF) is one of the key players in the process of angiogenesis. However, its underlying mechanism remains unclear. Mg2+ is the most abundant intracellular divalent cation in the body and plays critical roles in many cell functions. We investigated the effect of VEGF on intracellular Mg2+ in human umbilical vein endothelial cells (HUVECs). VEGF-A165 increased the intracellular Mg2+ concentration ([Mg2+]i) in a dose-dependent manner, with or without extracellular Mg2+, and the increase of [Mg2+]i was blocked by pretreatment with SU1498, tyrosine kinase inhibitors (tyrphostin A-23 and genistein), phosphatidylinositol 3-kinase (PI3K) inhibitors (wortmannin and LY294002) or phospholipase Cgamma (PLCgamma) inhibitor (U73122). In contrast, mitogen-activated protein kinase inhibitors (SB202190 and PD98059) had no effect on the VEGF-induced [Mg2+]i increase. These results suggest that VEGF-A165 increases the [Mg2+]i from the intracellular Mg2+ stores through the tyrosine kinase/PI3K/PLCgamma-dependent signaling pathways.