Differential regulation of multiple steps in inositol 1,4,5- trisphosphate signaling by protein kinase C shapes hormone-stimulated Ca2+ oscillations. [Metabolism]

June 15th, 2015 by Bartlett, P. J., Metzger, W., Gaspers, L. D., Thomas, A. P.

How Ca2+ oscillations are generated and fine-tuned to yield versatile downstream responses remains to be elucidated. In hepatocytes, G-protein coupled receptor (GPCR)-linked Ca2+ oscillations report signal strength via frequency, while Ca2+ spike amplitude and wave velocity remain constant. IP3 uncaging also triggers oscillatory Ca2+ release, but in contrast to hormones Ca2+ spike amplitude, width and wave velocity were dependent on [IP3] and were not perturbed by phospholipase C (PLC) inhibition. These data indicate that oscillations elicited by IP3 uncaging are driven by the biphasic regulation of the IP3 receptor (IP3R) by Ca2+, and unlike hormone-dependent responses do not require PLC. Removal of extracellular Ca2+ did not perturb Ca2+ oscillations elicited by IP3 uncaging, indicating that reloading of endoplasmic reticulum (ER) stores via plasma membrane Ca2+ influx does not entrain the signal. Activation and inhibition of PKC attenuated hormone-induced Ca2+ oscillations, but had no effect on Ca2+ increases induced by uncaging IP3. Importantly, PKC activation and inhibition differentially affected Ca2+ spike frequencies and kinetics. PKC activation amplifies negative feedback loops at the level of GPCR, PLC activity and/or IP3 metabolism to attenuate IP3 levels and suppress the generation of Ca2+ oscillations. Inhibition of PKC relieves negative feedback regulation of IP3 accumulation, and thereby shifts Ca2+ oscillations towards sustained responses or dramatically prolonged spikes. PKC downregulation attenuates phenylephrine-induced Ca2+ wave velocity, whereas responses to IP3 uncaging are enhanced. The ability to assess Ca2+ responses in the absence of PLC activity indicates that IP3R modulation by PKC regulates Ca2+ release and wave velocity.
  • Posted in Journal of Biological Chemistry, Publications
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