Small Rab GTPase Rab7b Promotes Megakaryocytic Differentiation by Enhancing IL-6 Production and STAT3-GATA-1 Association.

Abstract 1549

Interleukin 6 (IL-6) is a pleiotropic cytokine acting on a variety of cell types, and plays important roles in hematopoiesis. GATA-1 (GATA binding protein 1) is an important transcription factor involved in either megakaryocytic or erythrocytic differentiation. However, the mechanisms for IL-6-induced megakaryocytic differentiation and regulation of GATA-1 have not been fully elucidated. By using phorbol-12-myristate-13-acetate (PMA)-induced megakaryocytic differentiation of K562 cells as a model, we investigated the roles of Rab7b, a late endosome/lysosome-localized myeloid small GTPase, in megakaryocytic differentiation. We find that Rab7b can promote PMA-induced megakaryocytic differentiation, as evidenced by typical morphological alterations, increased fibronectin-specific adhesion, increased polyploidy formation, and increased expression of CD41a. The GTP-bound status and lysosomal localization of Rab7b are required for promotion of K562 megakaryocytic differentiation, which can be blocked by inhibitor of nuclear factor κB (NF-κB) and neutralizing antibodies for IL-6 and gp130. In Rab7b-silenced K562 cells, PMA-induced activation of NF-κB, IL-6 production and megakaryocytic differentiation are impaired. Furthermore, we demonstrate that IL-6-induced activation of signal transducer and activator of transcription 3 (STAT3) and the subsequent association of STAT3 with GATA-1 may contribute to PMA-induced and Rab7b-mediated transcriptional upregulation of megakaryocytic differentiation markers. Therefore, our data suggest that Rab7b may play important roles in megakaryopoiesis by activating NF-κB and promoting IL-6 production. Our study also indicates that the IL-6-induced association of STAT3 with GATA-1 may favor megakaryopoiesis.