Immunohistochemical and immunocytochemical localization of human phostensin

Phostensin, protein phosphatase 1 F‐actin cytoskeleton targeting subunit, is a protein phosphatase 1 (PP1) binding protein. Phostensin is an actin filament pointed end‐capping protein and is capable of modulating actin dynamics. Northern blot analysis of phostensin mRNA indicate that the expression is predominant in leukocytes and spleen. To study phostensin protein distribution, we created a monoclonal antibody that specifically recognizes the residues 88–125. In consistence with mRNA distribution, phostesin protein is specifically distributed in lymphoid tissues including spleen, thymus, lymph node, as evidenced by immunohistochemistry assays. Phostensin was also present in human leukemic cell lines. Confocal microscopy revealed that phostensin was localized in the cytoplasm of peripheral blood mononuclear cells, and co‐localized with actin. Taken together, our results suggested that phostensin was located in the cytoplasm of leukocyte cells, and modulated actin dynamics.