Tissue Distribution of Isoforms of Type-1 Protein Phosphatase PP1 in Mouse Tissues and Its Diabetic Alterations

Abstract

The amounts of four isoforms of the catalytic subunit of type-1 protein phosphatase, PP1α, PP1γl, PP1γ2, and PP1δ have been determined in extracts of various mouse tissues including brain, liver, skeletal muscle, kidney, small intestine, heart, lung, spleen, thymus, and testis by Western blot analysis. Immunoreactive bands for PP1 isoforms were detected at 39.5, 38.5, and 40 kDa for PPlα, PP1γ1, and PP1γ2, respectively, and at 39 and 37 kDa for PP1δ. The amount of PP1α was at comparable levels in all tissues examined except skeletal and heart muscles, in which it was detected slightly or not detectable, respectively. The amount of PP1γ1 was at higher levels in brain, small intestine, and lung, being 2 to 3 times those in other tissues except heart and spleen, in which PP1γ1 was not detectable. The amount of PP1γ2 was extremely large in testis, small in brain, lung, spleen, and thymus, but it was not detectable in the other tissues. The amount of PP1δ was at comparable levels in all the tissues except skeletal muscle, in which it was at a low but detectable level. Then, the amounts of the four PP1 isoforms were determined in non-obese diabetic (NOD) mice. The amounts of PP1α were progressively decreased in livers of NOD mice as a function of increasing concentrations of blood glucose, whereas the amounts of PP1γ1 and PP1δ were unchanged. These tissue-characteristic expression patterns and the diabetes-induced alteration strongly suggest different roles and significance of each isoform of type-1 protein phosphatase in these mouse tissues.