Digitalis and Digitalislike Compounds Down-Regulate Gene Expression of the Intracellular Signaling Protein 14-3-3 in Rat Lens

Na⁺,K⁺-ATPase activity in the epithelial layer is fundamental to the maintenance of ionic concentration gradients and transparency of the lens. Recently we have identified endogenous digitalislike compounds (DLC), 19-norbufalin and its peptide derivatives, in human cataractous lenses (Lichtstein et al. Eur J Biochem 216: 261-268, 1993). Lenses were treated with 10 nM ouabain, bufalin or 19-norbufalin derivative for 24 h and were compared to control lenses. Differential display analysis revealed that one of the down-regulated genes was 14-3-3 theta. Down-regulation was confirmed by Northern blot and by RT-PCR analysis. RT-PCR of additional 14-3-3 isoforms revealed that the eta and gamma isoforms of 14-3-3 are also down-regulated by ouabain, bufalin and 19-norbufalin derivative, whereas the zeta isoform is down-regulated only by bufalin. These results demonstrate that one of the consequences of Na⁺,K⁺-ATPase inhibition by exogenous or endogenous inhibitors is the down-regulation of mRNA transcripts encoding several isoforms of 14-3-3. Since the 14-3-3 proteins are multifunctional regulatory proteins, the reduction in the abundance of various isoforms will have profound effects on cell function. Furthermore, These results, together with the demonstration of digitalislike compounds in the normal lens, and their increased level in human cataractous lenses, strongly suggests their involvement in the molecular mechanisms responsible for cataract formation.