Calpain-3-mediated regulation of the Na⁺-Ca²⁺ exchanger isoform 3.
Ca(2+) disturbances are observed when Ca(2+)-dependent cysteine proteases malfunction, causing muscle weakness and wasting. For example, loss of calpain-3 (CAPN3) activity leads to limb-girdle muscular dystrophy 2A (LGMD2A). In neuronal excitotoxicity, the cleavage of the Na(+)-Ca(2+) exchanger isoform 3 (NCX3) has been associated with an increase in activity and elevation of the Ca(2+) content in the endoplasmic reticulum (ER). Since NCX3 is expressed in skeletal muscle, we evaluated the cleavage of different NCX3 splice variants by CAPN1 and CAPN3. Using Fura-2-based cellular Ca(2+) imaging, we showed for the first time that CAPN3 increases NCX3 activity and that only NCX3-AC, the variant predominantly expressed in skeletal muscle, is sensitive to calpain. The silencing of the endogenous CAPN1 and the expression of the inactive form of CAPN3 (C129S CAPN3) confirmed the specificity for CAPN1 and CAPN3. Functional studies revealed that cellular Ca(2+) uptake through the reverse mode of NCX3 was significantly increased independently of the mode of activation of the exchanger by either a rise in intracellular Ca(2+) ([Ca(2+)]i) or Na(+) ([Na(+)]i). Subsequently, the sensitivity to CAPN1 and CAPN3 could be abrogated by removal of the six residues coded in exon C of NCX3-AC. Additionally, mutation of the Leu-600 and Leu-601 suggested the presence of a cleavage site at Leu-602. The increased Ca(2+) uptake of NCX3 might participate in the Ca(2+) refilling of the sarcoplasmic reticulum (SR) after the excitation-contraction uncoupling following exercise and therefore be implicated in the impaired reticular Ca(2+) storage observed in LGMD2A.
From the Department of Physiology, Centre for System Biology and Bioenergetics, Radboud University Medical Center, PO Box 9101, 6500 HB, Nijmegen, The Netherlands.
Lauriane Y M
LY
Michel
From the Department of Physiology, Centre for System Biology and Bioenergetics, Radboud University Medical Center, PO Box 9101, 6500 HB, Nijmegen, The Netherlands.
Joost G J
JG
Hoenderop
From the Department of Physiology, Centre for System Biology and Bioenergetics, Radboud University Medical Center, PO Box 9101, 6500 HB, Nijmegen, The Netherlands. Rene.Bindels@radboudumc.nl.
René J M
RJ
Bindels
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002154:Calpain / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D059748:Proteolysis; D019831:Sodium-Calcium Exchanger / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D009124:Muscle Proteins; D020033:Protein Isoforms; C491101:Slc8a3 protein, mouse; D019831:Sodium-Calcium Exchanger; C105884:CAPN3 protein, human; D002154:Calpain; C484806:CAPN1 protein, human; D002118:Calcium
Alternative splicing; Calpain-3; Exercise; Muscle fatigue; Muscular dystrophy; Sodium-calcium exchange