Thiopurines Induce Oxidative Stress in T-Lymphocytes: A Proteomic Approach

Figure 4

Thiopurine induced oxidative stress and proteome regulation 6-MP and 6-TG treatment induced phosphorylation changes in GSTM3 and PRDX3 (redox regulators of cell) which can consequently reduce their ROS neutralization activity [32, 36]. Similarly, TPMT knockdown and thiopurine treatment downregulated expression of SOD1 which together with altered activity of GSTM3 and PRDX3 might result in enhanced ROS accumulation. ROS assays showed an increase in ROS level after 6-MP and 6-TG treatment. Increased ROS levels may cause mitochondrial dysfunction [59]. Persistent and increasing mitochondrial dysfunction can induce cellular cytotoxicity and apoptosis [59]. On the other hand, to cope with increasing oxidative stress, cells could activate their cellular antioxidant mechanisms [59] as suggested by the increased expression of the antioxidant proteins THIO [60], SOD2 [61], and CAT [39]. ROS accumulation also affects cytoskeleton [62], suggested by the altered cytoskeleton regulator proteins (expression of COF1 and PROF1 and phosphorylation of p-ARP2, p-COR1A) [30, 50, 52, 53]. Oxidative stress influences the cell cycle [63], and the observed reduced expression of STMN1 (a regulator of microtubule dynamics during meiosis) and decreased phosphorylation of PRS10 (involved in ATP-dependent degradation of ubiquitinated proteins) may be indicative of this phenomenon [43, 46]. We hypothesize that 6-MP and 6-TG treatment affect the activity of antioxidant proteins which results in increased oxidative stress and consequently mitochondrial dysfunction, as well as cytoskeleton and cell cycle disturbances which collectively contribute to thiopurine induced cytotoxicity.