Rapid 1α,25(OH)₂D₃ membrane-mediated activation of Ca²⁺/calmodulin-dependent protein kinase II in growth plate chondrocytes requires Pdia3, PLAA and caveolae

Abstract

1α,25-Dihydroxy vitamin D3 [1α,25(OH)₂D₃] regulates growth zone chondrocytes (GC) via classical steroid hormone receptor-mediated gene transcription and by initiating rapid membrane-mediated signaling pathways. 1α,25(OH)₂D₃ initiates its membrane effects via its specific membrane-associated receptor (Pdia3) in caveolae. 1α,25(OH)₂D₃ binding to Pdia3 leads to phospholipase-A₂ (PLA₂)-activating protein (PLAA) activation, stimulating PLA₂, resulting in prostaglandin E2 (PGE₂) release and protein kinase C activation. Recently, we reported that 1α,25(OH)₂D₃ rapidly activates Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) in GC cells. However, the roles of Pdia3, PLAA and caveolae in 1α,25(OH)₂D₃-dependent rapid activation of CaMKII are not clear. The aim of the present study was to evaluate the roles of Pdia3, PLAA and caveolae in 1α,25(OH)₂D₃ membrane-stimulated CaMKII activation. Pre-treating chondrocytes from the growth zone of the rat costochondral cartilage with antibodies against PLAA or Pdia3 blocked activation of CaMKII by 1α,25(OH)₂D₃. PLAA peptide rapidly activated CaMKII in GC cells. Caveolae disruption abolished CaMKII activation in response to 1α,25(OH)₂D₃ or PLAA peptide treatment. Immunoprecipitation studies showed increased CaM binding to PLAA in response to 1α,25(OH)₂D₃. The results indicated that Pdia3, PLAA and caveolae are required for rapid 1α,25(OH)₂D₃ membrane-mediated activation of CaMKII. 1α,25(OH)₂D₃ signaling via Pdia3 receptor triggered the interaction between PLAA and CaM suggesting that CaM may play a major role linking PLAA to CaMKII in membrane-mediated actions of 1α,25(OH)₂D₃.

• Caveolae
• non-genomic actions
• phospholipase A2 activating protein
• protein disulfide isomerase A3
• rapid actions
• secosteroid hormone