Abstract 987: Hematopoietic Stem Cell Differentiation to Megakaryocytes Affects Expression of MRP4 (ABCC4) and MRP5 (ABCC5), Transport Proteins for Signalling Molecules and Drugs
Background: We have recently provided evidence that the amphiphilic anion transporter MRP4 (ABCC4) is highly expressed in human platelets and located in delta-granules and plasma membrane and plays a substantial role in ADP storage and release. Platelets are formed by megakaryocytes, arising from pluripotent CD34+ progenitor cells. Therefore, we investigated the expression of MRP4 and the related transporter MRP5 (ABCC5) during the differentiation of hematopoietic stem cells.
Methods & Results: We assessed expression and localization of these transport proteins by real time RT-PCR and laser scanning immunofluorescence microscopy in a haematopoiesis model system using human CD34+ cells isolated from cord blood as well as leukapheresis samples. These cells were differentiated with cytokines along two pathways: megakaryocytic and myelomonocytic. The state of differentiation was determined by FACS staining using lineage specific surface markers. MRP4 expression increased significantly during the CD34+ cell-differentiation towards megakaryocytes and was also detected in mature bone marrow megakaryocytes. In contrast, expression of MRP4 and MRP5 was found to decrease during differentiation to mature leukocytes.
Conclusions: These results indicate that MRP4 and MRP5 expression is specifically regulated during hematopoiesis. The increase of MRP4 expression during the differentiation towards megakaryocytes is in accordance with the attainment of platelet specific functions and supports the role of MRP4 in establishing the content of platelets delta-granules.