Calcineurin A (Ca) Inhibition Supresses Protein Synthesis Via Amp Dependent Kinase (Ampk).

Abstract

Diabetes stimulates CA activity in the kidney and CA inhibitor cyclosporine A (CYA) or CAβ isoform knock-out (CAβ -/-) block diabetic renal hypertrophy.CA regulates the mammalian target of rapamycin (mTOR) to reduce protein synthesis (PS) during cardiac hypertrophy.To study this pathway, NRK-52E and SV40 transformed CAβ +/+ and -/- proximal tubule cell lines were treated with 10 nM epidermal growth factor (EGF) and/or 8 μM CYA. After 48 hrs of CYA in NRK-52E cells, EGF-induced protein/well was 30±4% lower with decreased PS (49±2%) rather than increased protein breakdown. In CAβ -/- cells, protein/well (20+2%) and PS (16 ±1%) were lower and CYA did not decrease PS further. In CAβ+/+ cells, CYA reduced PS 20+2%. However, CYA did not block mTOR signaling as measured by phosphorylation (P) at S2448 or by p70S6 kinase P at T389. CYA also did not alter the mTOR dependent pathway of macroautophagy. However, CYA in NRK-52E or CAβ -/- cells showed increased activation of the metformin-sensitive energy sensor, AMPK, as measured by P of T172 by ∼5- or>10-fold, respectively. AMPK reduces PS via P of eukaryotic elongation factor 2 (eEF2) at T356 and CYA increased eEF2 P by∼3 fold.We conclude CA inhibition reduces PS in renal hypertrophy via a novel pathway involving AMPK and eEF2 rather than by mTOR and p70S6 kinase. Activation of AMPK or altered energy metabolism via CAβ may be important in CA inhibitor nephrotoxicity.