Expression of the GPI-anchored receptor Prv-1 enhances thrombopoietin and IL-3-induced proliferation in hematopoietic cell lines

Prv-1 is a hematopoietic cell surface receptor that has been shown to be overexpressed in patients diagnosed with polycythemia vera (PV) and essential thrombocythemia (ET), yet its cellular function remains unclear. In this study, we assessed the role of Prv-1 in thrombopoietin (Tpo)/Mp1 signaling with the goal of identifying molecular mechanisms which augment Tpo-induced proliferation. By engineering the cytokine-dependent hematopoietic cell line BaF3 to express both Prv-1 and wild-type or mutant forms of Mp1, we were able to follow the time Course of Tpo-dependent proliferation. We report that the overexpression of Prv-1 increased Tpo as well as IL-3-induced proliferation of BaF3/Mp1 and BaF3 cells. Cells co-expressing Prv-1 and an Mp1 receptor containing a Box I motif mutation, which fails to activate Jak2, was completely deficient in Tpo-dependent proliferation. In addition, BaF3 and BaF3/Prv-1 cells Stimulated with IL-3 in the presence of the Jak2 inhibitor, AG490, abrogated the proliferative response, indicating that Prv-1 requires a functional Jak2 for its signaling activities. Western blot analysis showed an increase in Tpo and IL-3-induced Stat3 and Stat5 tyrosine phosphorylation in BaF3/Mp1 and BaF3 cells expressing Prv-1. These results indicate a novel function for Prv-1 as a signaling molecule in cytokine signaling cascades and may lead to a greater understanding of the mechanism of overexpression of Prv-1 in myeloproliferative disorders. (C) 2007 Elsevier Ltd. All rights reserved.