Localization and characterization of calcineurin in bovine eye

Abstract

PURPOSE. There are several aspects of the visual system that may be regulated by Ca 2ϩ-and calmodulin (CaM)-stimulated protein phosphatase. In the present study, the distribution and characterization of calcineurin (CaN) in bovine eye was determined. METHODS. Whole bovine eyes were either homogenized for purification or regionally dissected to determine CaN localization and activity. Dissected tissues were homogenized and Western blot analysis performed, using polyclonal anti-CaN antibodies, and assayed using p-nitrophenyl phosphate (PNPP) as a substrate to determine the dephosphorylation activity of CaN. Fresh samples were then prepared for immunohistochemistry and probed with polyclonal anti-CaN antibodies. RESULTS. CaN was found to be present in all eye tissues, although activity and protein expression varied. The highest levels of CaN activity and protein expression were found in the optic nerve, retina, and cornea. Immunohistochemical methods displayed similar results with additional staining of the optic nerve vasculature. Assays of purified CaN demonstrated that bovine eye CaN had regulatory properties similar to CaN isolated from other tissues. Probing eye tissues with CaN A isoform-specific antibodies demonstrated that eye tissues displayed variable distributions of the CaN A␣ and CaN A␤ isoforms. CONCLUSIONS. The presence of CaN in the bovine eye provides a physiological pathway by which the phosphorylated state of proteins and intracellular Ca 2ϩ concentrations can be coordinated. The authors propose that CaN is involved in the immunologic privilege of the cornea, retinal signal transduction, and the toxic effects of immunosuppressants on the eye. Further in vivo studies of CaN function are necessary to understand the contributions of CaN to ocular physiology. (Invest Ophthalmol Vis Sci. 2002;43:15-21) C alcineurin (CaN) is an 80-kDa protein phosphatase that is regulated by intracellular Ca 2ϩ concentrations and is capable of regulating a variety of protein substrates by dephosphorylation. The inositol 1,4,5-trisphosphate (IP3) receptor 1 and N-methyl-D-aspartate receptors 2 are deactivated on dephos-From the