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Int J Biol Sci 2016; 12(1):18-29. doi:10.7150/ijbs.13549

Research Paper

Excess Nitric Oxide Activates TRPV1-Ca2+-Calpain Signaling and Promotes PEST-dependent Degradation of Liver X Receptor α

Jin-Feng Zhao1, Song-Kun Shyue2, Tzong-Shyuan Lee1,3✉

1. Department of Physiology, National Yang-Ming University, Taipei, 11221, Taiwan.
2. Cardiovascular Division, Institute of Biomedical Sciences, Academia Sinica, Taipei, 11529, Taiwan.
3. Genome Research Center, National Yang-Ming University, Taipei, 11221, Taiwan.

Abstract

Excess nitric oxide (NO) deregulates cholesterol metabolism in macrophage foam cells, yet the underlying molecular mechanism is incompletely understood. To investigate the mechanism, we found that in macrophages, treatment with NO donors S-nitroso-N-acetyl-D,L-penicillamine (SNAP) or diethylenetriamine/nitric oxide induced LXRα degradation and reduced the expression of the downstream target of LXRα, ATP-binding cassette transporter A1 (ABCA1), and cholesterol efflux. In addition, SNAP induced calcium (Ca2+) influx into cells, increased calpain activity and promoted the formation of calpain-LXRα complex. Pharmacological inhibition of calpain activity reversed the SNAP-induced degradation of LXRα, down-regulation of ABCA1 and impairment of cholesterol efflux in macrophages. SNAP increased the formation of calpain-LXRα complex in a Pro-Glu-Ser-Thr (PEST) motif-dependent manner. Truncation of the PEST motif in LXRα abolished the calpain-dependent proteolysis. Removal of extracellular Ca2+ by EGTA or pharmacological inhibition of TRPV1 channel activity diminished SNAP-induced increase in intracellular Ca2+, calpain activation, LXRα degradation, ABCA1 down-regulation and impaired cholesterol efflux. In conclusion, excess NO may activate calpain via TRPV1-Ca2+ signaling and promote the recognition of calpain in the PEST motif of LXRα, thereby leading to degradation of LXRα and, ultimately, downregulated ABCA1 expression and impaired ABCA1-dependent cholesterol efflux in macrophages.

Keywords: nitric oxide, calcium, TRPV1, calpain, ABCA1, LXRα, macrophages

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How to cite this article:
Zhao JF, Shyue SK, Lee TS. Excess Nitric Oxide Activates TRPV1-Ca2+-Calpain Signaling and Promotes PEST-dependent Degradation of Liver X Receptor α. Int J Biol Sci 2016; 12(1):18-29. doi:10.7150/ijbs.13549. Available from http://www.ijbs.com/v12p0018.htm