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(Circulation Research. 2007;100:874.)
© 2007 American Heart Association, Inc.

Cellular Biology

Alternative Splicing of Ryanodine Receptors Modulates Cardiomyocyte Ca²⁺ Signaling and Susceptibility to Apoptosis

Christopher H. George, Sarah A. Rogers, Benedicte M.A. Bertrand, Richard E.A. Tunwell, N. Lowri Thomas, Derek S. Steele, Eryl V. Cox, Christopher Pepper, Carolyn J. Hazeel, William C. Claycomb, F. Anthony Lai

From the Department of Cardiology (C.H.G., S.A.R., B.M.A.B., N.L.T., E.V.C., C.J.H., F.A.L.), Wales Heart Research Institute, Cardiff University, UK; Department of Physiology (R.E.A.T.), University College London, UK; Institute of Membrane and Systems Biology (D.S.S.), University of Leeds, UK; Department of Haematology (C.P.), Cardiff University School of Medicine, UK; and Department of Biochemistry (W.C.C.), Louisiana State University, New Orleans.

Correspondence to Dr Christopher H. George, Department of Cardiology, Wales Heart Research Institute, School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, UK. E-mail georgech{at}cf.ac.uk

Ca²⁺ release via type 2 ryanodine receptors (RyR2) regulates cardiac function. Molecular cloning of human RyR2 identified 2 alternatively spliced variants, comprising 30- and 24-bp sequence insertions; yet their role in shaping cardiomyocyte Ca²⁺ signaling and cell phenotype is unknown. We profiled the developmental regulation and the tissue and species specificity of these variants and showed that their recombinant expression in HL-1 cardiomyocytes profoundly modulated nuclear and cytoplasmic Ca²⁺ release. All splice variants localized to the sarcoplasmic reticulum, perinuclear Golgi apparatus, and to finger-like invaginations of the nuclear envelope (nucleoplasmic reticulum). Strikingly, the 24-bp splice insertion that was present at low levels in embryonic and adult hearts was essential for targeting RyR2 to an intranuclear Golgi apparatus and promoted the intracellular segregation of this variant. The amplitude variability of nuclear and cytoplasmic Ca²⁺ fluxes were reduced in nonstimulated cardiomyocytes expressing both 30- and 24-bp splice variants and were associated with lower basal levels of apoptosis. Expression of RyR2 containing the 24-bp insertion also suppressed intracellular Ca²⁺ fluxes following prolonged caffeine exposure (1 mmol/L, 16 hours) that protected cells from apoptosis. The antiapoptotic effects of this variant were linked to increased levels of Bcl-2 phosphorylation. In contrast, RyR2 containing the 30-bp insertion, which was abundant in human embryonic heart but was decreased during cardiac development, did not protect cardiomyocytes from caffeine-evoked apoptosis. Thus, we provide the first evidence that RyR2 splice variants exquisitely modulate intracellular Ca²⁺ signaling and are key determinants of cardiomyocyte apoptotic susceptibility.

Key Words: ryanodine receptor • Ca²⁺ • alternative splicing • cardiomyocyte • apoptosis

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One Gene, Many Proteins: Alternative Splicing of the Ryanodine Receptor Gene Adds Novel Functions to an Already Complex Channel Protein

Héctor H. Valdivia
Circ. Res. 2007 100: 761-763. [Full Text] [PDF]

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