Overexpression of transglutaminase 2 accelerates the erythroid differentiation of human chronic myelogenous leukemia K562 cell line through PI3K/Akt signaling pathway.

Transglutaminase 2 (TG2) is a GTP-binding protein with transglutaminase activity. Despite advances in the characterization of TG2 functions and their impact on cellular processes, the role of TG2 in Human chronic myelogenous leukemia K562 cell line is still poorly understood. To understand the biological significance of TG2 during the differentiation of K562 cells, we established and characterized K562 cells that specifically express TG2. Non-transfected K562 cells showed the increase of membrane-bound-TG2 level after 3 days in the response to Hemin and all trans-retinoic acid (tRA), indicating that membrane recruitment of TG2 is occurred during the erythroid differentiation. However, membrane recruitment of TG2 in TG2-transfected cells revealed within earlier time period, compared with that in vector-transfected cells. The ability of membrane-bound-TG2 to be photoaffinity-labeled with [alpha-32P]GTP was also increased in TG2-transfected cells. TG2-transfected cells activated Akt phosphorylation and inactivated ERK1/2 phosphorylation, compared with vector-transfected cells. Furthermore, phosphorylation of CREB, one of the Akt substrates, was increased in TG2-transfected cells and this phenomenon was confirmed by RT-PCR analysis of several marker genes related with erythroid lineage in the absence of PI3K specific inhibitor, Wortmannin, indicating that PI3K/Akt signaling pathway also involved in the differentiation of the cell. Finally, as results of benzidine positive staining as well as hemoglobinization analysis, overexpression of TG2 revealed acceleration of the erythroid differentiation of K562 cells. Taken together, there was no increased TG2 expression level in the response of Hemin/tRA and delayed differentiation in vector transfected cells than in TG2-transfected cells, suggesting that suppression of TG2 expression may retard the erythroid differentiation of K562 cells. Therefore, our study may give a new insight for another aspect of the development of this disease.