Promoted megakaryocytic differentiation of K562 cells through oxidative stress caused by near ultraviolet irradiation

Reactive oxygen species (ROS) have been proven to be important activators for various cellular activities, including cell differentiation. Several reports showed the necessity of ROS during cell differentiation of the megakaryocytic (MK) lineage. In this study, we employed near ultraviolet (near-UV) irradiation to generate endogenous oxidative stress in an MK differentiation process of K562 cells with phorbol 12-myristate 13-acetate (PMA) induction. A significant increase in the intracellular ROS level was detected on day 1 after near-UV irradiation. In the initial stage of differentiation, a shifted fraction of G(1) and G(2) phase cells was obtained using near-UV irradiation, giving an increased percentage of G(2) phase cells (up from 31.1 to 68.7%). The near-UV irradiation-induced upregulation of the p21 gene, which is a cell cycle inhibitor, suggested that the G(2) phase cells were prevented from undergoing cell division. It was found that the percentage of high ploidy (8N and 16N) cells was enhanced significantly at the later stage of the K562 cell culture with near-UV irradiation. Moreover, time-lapse analysis showed that near-UV irradiation encouraged the expression of CD41, a specific surface marker of megakaryocytes. This is the first report that the elevated oxidative stress through the near-UV irradiation promoted the MK differentiation of PMA-induced K562 cells.