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  • It has been reported that Daxx an interacting partner


    It has been reported that Daxx, an interacting partner of MCRS2/MSP58, promotes ASK1 activation following direct interaction with ASK1 [10], [11]. However, it has not been determined whether MCRS2 is involved in ASK1 signalling. In this study, we identified the direct interaction between MCRS2 and ASK1, and we examined the effect of MCRS2 upon oxidative stress-induced ASK1 activation. As a result, we found that MCRS2 functions as a negative regulator of stress-induced ASK1 activation.
    Materials and methods
    Discussion MCRS2/MSP58 has been reported to associate with some cellular functions such as telomerase inhibition [1], transcriptional regulation [2], [3], and cellular transformation [5]. However, the physiological function of MCRS2 is still not well understood. Our results demonstrate for the first time that MCRS2 interacts with ASK1 and functions as a negative regulator of the ASK1-mediated apoptosis pathway. In this study, we found that MCRS2 interacts with ASK1 directly and co-localises with ASk1 in the cytoplasm (Fig. 1, Fig. 2). Since single Flag-MCRS2 was mostly displayed on the nucleus, we are interested to examine whether MCRS2 could be redistributed from the nucleus to the cytoplasm induced by H2O2. However, H2O2 stimulation induced a speckled pattern of MCRS2 in the nucleus, rather than a translocation from the nucleus to the cytoplasm (Supplementary Fig. S1). This result suggested that endogenous MCRS should exist in the cytoplasm relying on the interaction with ASK1. In this case, MCRS2 could inhibit the phosphorylation level of ASK1 induced by H2O2. Some papers have showed that endogenous MCRS2/MSP58 lies predominantly in the nucleus, whereas a small fraction is detected in the cytoplasm [13]. In our paper, we provided the evidences that both endogenous MCRS2 and Flag-MCRS2 directly interact with ASK1 in H2O2 unstimulated RQ-00203078 (Fig. 1). These results suggested that the endogenous MCRS2 may remain in cytoplasm partially, and the interaction between endogenous MCRS2 and ASK1 may occur in the cytoplasm which does not depend on the stimulation of H2O2. Based on our findings, we propose a model for the negative regulation of ASK1 activity by MCRS2 (Fig. 7D). At baseline conditions, MCRS2 may interact with ASK1 in the cytoplasm and form a complex to inhibit ASK1 activation. Upon oxidative stress, MCRS2 is released from the complex and degraded in a proteasome-dependant manner while ASK1 is phosphorylated. Moreover, activated ASK1 can promote MCRS2 degradation, resulting in the accelerated activation of ASK1 signalling. Recently, it was reported that MSP58 expression is elevated in gliomas and colorectal carcinomas, and down-regulation of MSP58 by siRNA decreases tumour growth, migration and invasion, suggesting a pro-oncogenic role for MSP58 [12], [16]. However, the exact mechanism of MSP58 in promoting tumorigenesis remains unclear. On the contrary, ASK1 has been reported to be a tumour suppressor in colon and liver cancer development through the regulation of stress-induced apoptosis and inflammation [17], [18]. Based on our results, it is tempting to propose that increased MCRS2/MSP58 expression in cancer cells may play a critical role in the inhibition of ASK1 activation, resulting in enhanced resistance against stress-induced apoptosis via the ASK1 pathway. Further studies on the mechanisms by which MCRS2 regulates the ASK1 pathway may contribute to understanding the significance of MCRS2 in tumourgenesis.
    Financial support
    Acknowledgments We thank Dr. Gang Pei (Institute of Biochemistry and Cell Biology, CAS, Shanghai, China) for providing the pcDNA3-HA-ASK1 and pcDNA3-HA-ASK1 (K709R) plasmids. This work was supported by grants from the National Key S&T Special Project of China (Nos. 2012ZX10002009 and 2012CB519002) and the National Natural Sciences Foundation of China (No. 30871341).
    Introduction Hepatic ischemia reperfusion (I/R) is cause of hepatic damage and may lead to liver failure upon liver resection or transplantation. Steatosis, the most frequent hepatic pathology in western countries, greatly augments ischemia/reperfusion (I/R) injury and is associated with higher morbidity and mortality upon major liver surgery [1], [2], [3]. Steatosis is a major risk factor not only in liver resection, but also in transplantation, where the shortage of donors have extended the criteria of graft acceptance also to marginal fatty livers. Thus therapeutic procedures to minimize I/R injury of steatotic liver are increasingly needed [1], [2].