Opposing regulation of megakaryopoiesis by LPA receptors 2 and 3 in K562 human erythroleukemia cells.

Erythrocytes and megakaryocytes (MK) are derived from a common progenitor that undergoes lineage specification. Lysophosphatidic acid (LPA), a lipid growth factor was previously shown to be a regulator for erythropoietic process through activating LPA receptor 3 (LPA3). However, whether LPA affects megakaryopoiesis remains unclear. In this study, we used K562 leukemia cell line as a model to investigate the roles of LPA in MK differentiation. We demonstrated that K562 cells express both LPA2 and LPA3, and the expression levels of LPA2 are higher than LPA3. Treatment with phorbol 12-myristate 13-acetate, a commonly used inducer of megakaryopoiesis, reciprocally regulates the expressions of LPA2 and LPA3. By pharmacological blockers and knockdown experiments, we showed that activation of LPA2 suppresses whereas, LPA3 promotes megakaryocytic differentiation in K562. The LPA2-mediated inhibition is dependent on ß-catenin translocation, whereas reactive oxygen species (ROS) generation is a downstream signal for activation of LPA3. Furthermore, the hematopoietic transcriptional factors GATA-1 and FLI-1, appear to be involved in these regulatory mechanisms. Taken together, our results suggested that LPA2 and LPA3 may function as a molecular switch and play opposing roles during megakaryopoiesis of K562 cells.

Pharmacological activation of lysophosphatidic acid receptors regulates erythropoiesis.

Lysophosphatidic acid (LPA), a growth factor-like phospholipid, regulates numerous physiological functions, including cell proliferation and differentiation. In a previous study, we have demonstrated that LPA activates erythropoiesis by activating the LPA 3 receptor subtype (LPA3) under erythropoietin (EPO) induction. In the present study, we applied a pharmacological approach to further elucidate the functions of LPA receptors during red blood cell (RBC) differentiation. In K562 human erythroleukemia cells, knockdown of LPA2 enhanced erythropoiesis, whereas knockdown of LPA3 inhibited RBC differentiation. In CD34(+) human hematopoietic stem cells (hHSC) and K526 cells, the LPA3 agonist 1-oleoyl-2-methyl-sn-glycero-3-phosphothionate (2S-OMPT) promoted erythropoiesis, whereas the LPA2 agonist dodecyl monophosphate (DMP) and the nonlipid specific agonist GRI977143 (GRI) suppressed this process. In zebrafish embryos, hemoglobin expression was significantly increased by 2S-OMPT treatment but was inhibited by GRI. Furthermore, GRI treatment decreased, whereas 2S-OMPT treatment increased RBC counts and amount of hemoglobin level in adult BALB/c mice. These results indicate that LPA2 and LPA3 play opposing roles during RBC differentiation. The pharmacological activation of LPA receptor subtypes represent a novel strategies for augmenting or inhibiting erythropoiesis.