Paclitaxel accelerates spontaneous calcium oscillations in cardiomyocytes by interacting with NCS-1 and the InsP3R

Abstract

Paclitaxel (Taxol) is a microtubule-stabilizing compound that is used for cancer chemotherapy. However, Taxol administration is limited by serious side effects including cardiac arrhythmia, which cannot be explained by its microtubule-stabilizing effect. Recently, neuronal calcium sensor 1 (NCS-1), a calcium binding protein that modulates the inositol-1,4,5-trisphosphate receptor (InsP 3 R), was described as a binding partner of Taxol and as a substrate of calpain. We examined calcium signaling processes in cardiomyocytes after treatment with Taxol to investigate the basis of Taxol-induced cardiac arrhythmia. After treating isolated neonatal rat ventricular myocytes with a therapeutic concentration of Taxol for several hours live cell imaging experiments showed that the frequency of spontaneous calcium oscillations significantly increased. This effect was not mimicked by other tubulin-stabilizing agents. However, it was prevented by inhibiting the InsP 3 R. Taxol treated cells had increased expression of NCS-1, an effect also detectable after Taxol administration in vivo. Short hairpin RNA mediated knock down of NCS-1 decreased InsP 3 R dependent intracellular calcium release, whereas Taxol treatment, that increased NCS-1 levels, increased InsP 3 R dependent calcium release. The effects of Taxol were ryanodine receptor independent. At the single channel level Taxol and NCS-1 mediated an increase in InsP 3 R activity. Calpain activity was not affected by Taxol in cardiomyocytes suggesting a calpain independent signaling pathway. In short, our study shows that Taxol impacts calcium signaling and calcium oscillations in cardiomyocytes through NCS-1 and the InsP 3 R.

Neuronal Calcium Sensor-1 Promotes Immature Heart Function and Hypertrophy by Enhancing Ca 2+ Signals

“…This finding is consistent with those of previous reports that have demonstrated that NCS-1 enhances IP 3 R activity when monitored as the activity of single channels and as Ca 2ϩ transients in intact cells. 23,25 In addition, the present experiments using the overexpression system were able to directly demonstrate that IP 3 R activation results in CaMKII-␦ phosphorylation, and this was further enhanced by NCS-1 overexpression ( Figures 7C and 7D), which supports a functional link between NCS-1, IP 3 R, and CaMKII activation. The present experiments showed that CaMKII-␦ and NCS-1, which were overexpressed in HEK293 cells, did not coimmunoprecipitate or colocalize with each other (Online Figure VI), which rules out possible direct interactions between NCS-1 and CaMKII-␦ independent of the effects of NCS-1 on IP 3 R. Taken together, these results suggest that NCS-1-IP 3 R interactions could serve as a Ca 2ϩ source for the activation of CaMKII, leading to a higher rate of SR Ca 2ϩ pumping and release and inducing global Ca 2ϩ signaling, thus promoting EC coupling in immature hearts (Online Figure VII depicts a possible signaling pathway).…”

“…22 Recently, NCS-1 was reported to be involved in paclitaxel-induced spontaneous Ca 2ϩ oscillation in cardiomyocytes. 23 However, little evidence is available for its physiological and pathological roles in cardiac functions, possibly because of its relatively low expression in the adult heart. We previously detected high expression levels (comparable to the levels in neurons) of NCS-1 in immature hearts 17 and hypertrophic hearts overexpressing Na ϩ /H ϩ exchanger 24 (data not shown); therefore, we hypothesized that NCS-1 has a specific role in cardiac function, particularly at the immature stage and during progression of hypertrophy.…”

Microtubule Disorganization Affects the Mitochondrial Permeability Transition Pore in Cardiac Myocytes

“…In neonatal rat ventricular myocytes, paclitaxel accelerated spontaneous oscillatory changes in cytosolic Ca 2+ by interacting with InsP3R. 20 The effect of paclitaxel on mPTP was not blocked by the inhibiter of InsP3R in this study. Ca 2+ -releasing channels from the SR are different between neonatal and adult ventricular myocytes, and Ca 2+ release by InsP3R is not dominant in adult ventricular myocytes.…”

“…19 In neonatal cardiomyocytes, paclitaxel accelerates spontaneous Ca 2+ oscillations via InsP3R. 20 Thus, we investigated whether paclitaxel-induced mPTP opening was dependent on InsP3R. For this purpose, 2-aminoethoxydiphenyl borate (2-APB; 20 μmol/L), a blocker of InsP3R, was used.…”

Metabolic amplification of insulin secretion by glucose is independent of β-cell microtubules

“…Here, we found that pretreatment with taxol completely stabilized microtubules in mouse islets, inhibited insulin secretion induced by KCl, tolbutamide, or glucose, but also attenuated the rise in [Ca 2ϩ ] c produced by the three secretagogues. Microtubuleindependent effects of taxol on Ca 2ϩ release from the endoplasmic reticulum have been described in neural cells and cardiomyocytes (3,62), but we are not aware of effects on voltage-dependent calcium channels. Whatever the underlying mechanism, the small decrease of [Ca 2ϩ ] c pro- duced by taxol probably contributed to the partial inhibition of secretion.…”