CYCLOSPORINE-A DECREASES THE PROTEIN LEVEL OF THE CALCIUM-BINDING PROTEIN CALBINDIN-D 28KDA IN RAT-KIDNEY

Despite the widespread use of cyclosporine A (CsA), its mechanism of a ction and side effects are not yet completely understood. There exists a large body of evidence suggesting that disturbance of calcium homeo stasis is a critical step in the cascade of cellular and molecular eve nts induced by the drug. As recently shown in our laboratory by two-di mensional protein gel electrophoresis (2-DE) analysis of kidney homoge nates, CsA induced numerous changes in several kidney proteins. One ki dney protein in particular was shown to be strongly down-regulated by the drug. In this work we report the identification of the strongly de creased kidney protein as calbindin-D 28kDa, a vitamin D-dependent cal cium-binding protein associated with calcium handling by cells. The as signment of the down-regulated protein spot is based on its internal a mino acid sequence analysis and its specific reaction with a monoclona l antibody raised against calbindin-D 28kDa. In kidney homogenates of male Wistar rats treated with 50 mg/kg/d CsA for up to 28 days, calbin din levels were measured by ELISA and were shown to be continuously de creased with prolonged CsA treatment. To our knowledge, this is the fi rst report describing the effect of CsA on kidney calbindin-D 28kDa pr otein levels. Further studies are needed to elucidate whether the CsA- mediated down-regulation of the calcium-binding protein calbindin-D 28 kDa may be a critical factor for the renal adverse effects induced by this drug.