Abstract
Abstract: :
Purpose: Protein kinase CK2 (casein kinase 2) is a ubiquitous serine/threonine protein kinase that phosphorylates more than 300 substrates and is involved in a wide variety of biological processes. Our previous data showed that tube formation by cultured retinal endothelial cells, their migration and secondary sprouting could be blocked by CK2 inhibitors. These observations imply that CK2 may in some way be involved in retinal angiogenesis that is impaired in some pathological conditions, such as diabetic retinopathy. Our purpose was to identify the expression patterns of CK2 in normal and diabetic retinal cells. Methods: Localization of CK2 in human retinal cells was studied by immunohistochemistry on retinal sections using specific antibodies to a catalytic α–subunit of CK2. Results: A panel of specific antibodies to human CK2α was utilized for immunohistochemical study of human retinas. Although in Western blot analyses most of the antibodies tested here were capable of specifically reacting with commercial purified CK2, only two antibodies showed good immunoreactivity with frozen sections of human retina. The two anti–CK2α monoclonal antibodies (mAb 1AD9 and D8E) showed staining of macroglial cells as proved by co–distribution with the corresponding markers (vimentin for Müller cells, and GFAP for astrocytes). The immunostaining with 1AD9 antibody was confined to "tangential" processes running in the main area of astrocyte location, the inner retina, often in close association with vasculature. This pattern of immunostaining was identical to that of the anti–GFAP, a marker for astrocytes. Specificity of the immune reaction was corroborated by depleting the antibody with purified CK2. D8E antibody stained both the endfeet of Müller cells (as did the anti–vimentin antibody) and the "tangential" processes of astrocytes. Neither of the antibodies showed significant differences between normal and diabetic retinas in the distribution of CK2α in macroglial cells. Conclusions: In the human retina, CK2 is expressed primarily in macroglia. Both anti–CK2α mAbs co–distribute in labeling tangential astroglial processes, whereas Müller cell endfeet are immunostained solely by D8E mAb. We presume that the two antibodies, which recognize different epitopes in CK2α, may be able to partially discriminate in cell type–specific manner between hypothetical conformational variants of the enzyme that differ in displaying the two antigenic determinants.
Keywords: Muller cells • diabetic retinopathy • immunohistochemistry