Objective To test whether in the absence of actin, actin-binding proteins such as caldesmon, calponin, and tropomyosin interact with the myosin of unphosphorylation, Ca 2+ -dependent phosphorylation (CDP), and Ca 2+ -...Objective To test whether in the absence of actin, actin-binding proteins such as caldesmon, calponin, and tropomyosin interact with the myosin of unphosphorylation, Ca 2+ -dependent phosphorylation (CDP), and Ca 2+ -independent phosphorylati-on (CIP) and stimulate myosin Mg 2+ -ATPase activities. Methods Mg 2+ -ATPase activities were measured to evaluate the effects of caldesmon, calponin, and tropomyosin on the myosin in unphosphorylation, CDP by myosin light chain kinase (MLCK), and CIP by MLCK. Results (1) At different incubation-time, i.e., 5, 10, 20, 40, and 60 minutes, the highest Mg 2+ -ATPase activity was ob-served when myosin was in the state of CDP, the medium was CIP of myosin, and the lowest was the unphosphorylated myosin. (2) In the absence of caldesmon, calponin, and tropomyosin, the Mg 2+ -ATPase activities from high to low were in the following order: CDP, CIP, and unphosphorylated myosin. However, in the presence of caldesmon, calponin, and tropo-myosin, the order of relative value of Mg 2+ -ATPase activities from high to low was unphosphorylated, CIP, and CDP of myosin respectively compared to the corresponding controls. Conclusions The results propose that caldesmon, calponin, and tropomyosin are capable of stimulating Mg 2+ -ATPase activity of smooth muscle myosin in Ca 2+ -independent manner, since Ca 2+ is not obligating for the stimulating effects of the three proteins. The common characteristic of the three proteins is that when myosin activities are low, their activations are relatively strong and this property might be involved in smooth muscle tension keeping.展开更多
The effect of U50488, a selective K-opioid receptor agonist, on cardiac rhythm in the isolated perfused rat heart and intracellular calcium ([Ca2+] i) in the single ventricular myocyte were studied. The results showed...The effect of U50488, a selective K-opioid receptor agonist, on cardiac rhythm in the isolated perfused rat heart and intracellular calcium ([Ca2+] i) in the single ventricular myocyte were studied. The results showed that U50488 can induce arrhythmias dose-dependently in the isolated perfused rat heart and increase [ Ca2 + ] i in the single ventricular myocyte. The effect of U50488 can be blocked by a selectivek-receptor antagonist, nor-binaltorphimine. The arrhythmogenic effects and the increase of [ Ca2+]i induced by U50488 were blocked by U73122, neomycin and streptomycin, which are selective phospolipase C inhibitors, but not by U73433, the inactive structural analog of U73122. These results demonstrated that the arrhythmogenic effect of cardiac K-receptor is due to activation of phosphoinositol/Ca2+ pathway.展开更多
Overexpression of the MDM2 oncogene and mutations in the p53 tumor suppressor commonly occur in hepatocellular carcinoma(HCC)and are associated with increased mortality due to this disease.Inhibiting MDM2 has been dem...Overexpression of the MDM2 oncogene and mutations in the p53 tumor suppressor commonly occur in hepatocellular carcinoma(HCC)and are associated with increased mortality due to this disease.Inhibiting MDM2 has been demonstrated to be a valid approach for the treatment of HCC.However,most of the MDM2 inhibitors evaluated to date have been designed to block the MDM2 and p53 binding,and have limited efficacy against tumors with mutant or deficient p53.In the present study,we developed a novel MDM2 inhibitor(termed SP141)that has direct effects on MDM2 and exerts anti-HCC activity independent of the p53 status of the cancer cells.We demonstrate that SP141 inhibits cell growth and prevents cell migration and invasion,independent of p53.Mechanistically,SP141 directly binds the MDM2 protein and promotes MDM2 degradation.The inhibition of MDM2 by SP141 also increases the sensitivity of HCC cells to sorafenib.In addition,in orthotopic and patient-derived xenograft models,SP141 inhibits MDM2 expression and suppresses tumor growth and metastasis,without any host toxicity.Furthermore,the inhibition of MDM2 by SP141 is essential for its anti-HCC activities.These results provide support for the further development of SP141 as a lead candidate for the treatment of HCC.展开更多
基金Supported by the National Natural Science Foundation of China ( 30070203).
文摘Objective To test whether in the absence of actin, actin-binding proteins such as caldesmon, calponin, and tropomyosin interact with the myosin of unphosphorylation, Ca 2+ -dependent phosphorylation (CDP), and Ca 2+ -independent phosphorylati-on (CIP) and stimulate myosin Mg 2+ -ATPase activities. Methods Mg 2+ -ATPase activities were measured to evaluate the effects of caldesmon, calponin, and tropomyosin on the myosin in unphosphorylation, CDP by myosin light chain kinase (MLCK), and CIP by MLCK. Results (1) At different incubation-time, i.e., 5, 10, 20, 40, and 60 minutes, the highest Mg 2+ -ATPase activity was ob-served when myosin was in the state of CDP, the medium was CIP of myosin, and the lowest was the unphosphorylated myosin. (2) In the absence of caldesmon, calponin, and tropomyosin, the Mg 2+ -ATPase activities from high to low were in the following order: CDP, CIP, and unphosphorylated myosin. However, in the presence of caldesmon, calponin, and tropo-myosin, the order of relative value of Mg 2+ -ATPase activities from high to low was unphosphorylated, CIP, and CDP of myosin respectively compared to the corresponding controls. Conclusions The results propose that caldesmon, calponin, and tropomyosin are capable of stimulating Mg 2+ -ATPase activity of smooth muscle myosin in Ca 2+ -independent manner, since Ca 2+ is not obligating for the stimulating effects of the three proteins. The common characteristic of the three proteins is that when myosin activities are low, their activations are relatively strong and this property might be involved in smooth muscle tension keeping.
文摘The effect of U50488, a selective K-opioid receptor agonist, on cardiac rhythm in the isolated perfused rat heart and intracellular calcium ([Ca2+] i) in the single ventricular myocyte were studied. The results showed that U50488 can induce arrhythmias dose-dependently in the isolated perfused rat heart and increase [ Ca2 + ] i in the single ventricular myocyte. The effect of U50488 can be blocked by a selectivek-receptor antagonist, nor-binaltorphimine. The arrhythmogenic effects and the increase of [ Ca2+]i induced by U50488 were blocked by U73122, neomycin and streptomycin, which are selective phospolipase C inhibitors, but not by U73433, the inactive structural analog of U73122. These results demonstrated that the arrhythmogenic effect of cardiac K-receptor is due to activation of phosphoinositol/Ca2+ pathway.
基金W.W. and R.Z. were partially supported by National Institutesof Health (NIH)/National Cancer Institute grants(R01 CA186662 and R01CA214019)W.W. and R.Z. were alsosupported by American Cancer Society (ACS) grant RSG-15-009-01-CDD. R.Z. was also supported by funds for Robert L.Boblitt Endowed Professor in Drug Discovery and researchfunds from College of Pharmacy and University of Houston.J.C., J.F., and X-R. Y. were supported by grants from theNational Natural Science Foundation of China (No.81272389, 81472674, 81502486). The content of this reportis solely the responsibility of the authors, and does notnecessarily represent the official views of the National Institutesof Health or other funding agencies.
文摘Overexpression of the MDM2 oncogene and mutations in the p53 tumor suppressor commonly occur in hepatocellular carcinoma(HCC)and are associated with increased mortality due to this disease.Inhibiting MDM2 has been demonstrated to be a valid approach for the treatment of HCC.However,most of the MDM2 inhibitors evaluated to date have been designed to block the MDM2 and p53 binding,and have limited efficacy against tumors with mutant or deficient p53.In the present study,we developed a novel MDM2 inhibitor(termed SP141)that has direct effects on MDM2 and exerts anti-HCC activity independent of the p53 status of the cancer cells.We demonstrate that SP141 inhibits cell growth and prevents cell migration and invasion,independent of p53.Mechanistically,SP141 directly binds the MDM2 protein and promotes MDM2 degradation.The inhibition of MDM2 by SP141 also increases the sensitivity of HCC cells to sorafenib.In addition,in orthotopic and patient-derived xenograft models,SP141 inhibits MDM2 expression and suppresses tumor growth and metastasis,without any host toxicity.Furthermore,the inhibition of MDM2 by SP141 is essential for its anti-HCC activities.These results provide support for the further development of SP141 as a lead candidate for the treatment of HCC.
