ginsenoside rh2 Transforming growth factor TGF signaling is

Transforming growth factor β (TGF-β) signaling is closely related to DNA damage repair regulation (Mitra et al., 2013). Studies have shown that TGF-β signaling can suppress BRCA1-dependent repair of DSBs (Dubrovska et al., 2005). Activin A, a member of the TGF-β superfamily of cytokines, interacts with Activin type I (ALK 2, ALK 4, or ALK 7) and type II (Acvr2a and Acvr2b) receptors (Bondestam et al., 1999; Donaldson et al., 1992; Robson et al., 2008), and it participates in DNA damage repair. In premalignant cells, DSB damage results in Activin A-dependent induction of Cox-2, which is associated with a high level of γ-H2AX (Carlson et al., 2013; Fordyce et al., 2012). In ductal carcinoma, DNA damage response (shorter telomeres and γ-H2AX foci) is also associated with high level of Activin A (Fordyce et al., 2012). Additionally, in hESCs, Activin A can maintain pluripotency even without feeder layers (Beattie et al., 2005). In mESCs, Activin A signaling can promote cell proliferation (Ogawa et al., 2007). However, it remains unknown whether the maintenance of a stable status in ESCs is also related to the DNA damage repair function of Activin A signaling. DSB damage is the most toxic type of DNA damage (Valerie and Povirk, 2003). Homologous recombination-mediated repair (HRR) is thought to be used in ESCs to repair DSBs (Hasty et al., 1992; Shrivastav et al., 2008; Smih et al., 1995; Tichy et al., 2010). Rad51 family members, including Rad51, Rad51b, Rad5c, Rad51d, and so on, are evolutionarily conserved proteins that play important roles during HHR (Baumann et al., 1996; Chun et al., 2013; Kawabata et al., 2005; Thacker, 2005). Rad51 paralogs take part in SSB and DSB damage repair (Jensen et al., 2010, 2013). RAD51B is also a protein kinase regulating the function of cell cycle-related genes (Havre et al., 2000) and is a known molecule to promote HRR by participating in the Holliday junction process (Kawabata et al., 2005; Takata et al., 2000). Previous studies have shown that overexpression of Rad51b in Chinese hamster ovary cells causes a G1 delay and UV irradiation hypersensitivity (Havre et al., 1998). TGF-β signaling has also been reported to inhibit DNA damage repair by downregulating the expression of Rad51 in Mv1Lu epithelial cells (Kanamoto et al., 2002). However, it is unknown whether Rad51 paralogs can regulate both the DNA damage repair and ginsenoside rh2 or even maintain their balance in mESCs. Additionally, the upstream regulators of Rad51 paralogs in mESCs are unclear. MicroRNAs (miRNAs) are posttranscriptional modulators of gene expression and are connected to the transcriptional regulatory circuitry of mESCs (Marson et al., 2008). Several miRNAs target DNA repair-related factors and influence DNA damage repair. Studies have shown that UV damage promotes miRNA expression in a partially ataxia telangiectasia mutated kinase (ATM)/ataxia telangiectasia and Rad3-related kinase-independent manner (Pothof et al., 2009). Overexpression of miR-24 attenuates H2AX, leading to high sensitivity to irradiation and reduced repair capacity (Lal et al., 2009). miRNAs can also regulate TGF-β signaling. miR-302/367 can modulate BMP signaling, which supports self-renewal by targeting BMP inhibitors in hESCs (Lipchina et al., 2011; Qi et al., 2004). However, there is limited understanding of miRNA modulation of these signaling pathways to regulate DNA damage repair to maintain self-renewal during ESC proliferation, which differs from differentiated cells (Tichy and Stambrook, 2008). In the present study, we found that miR-590 inhibits Activin signaling by directly targeting Acvr2a to inhibit the expression of Rad51b, balancing the DNA damage repair and rapid proliferation of ESCs.
Results
Discussion Rapid proliferation can maintain the self-renewal of ESCs, but it can also result in DNA damage that leads to catastrophic mutations affecting the differentiation of organisms and causing mutations to be passed to progeny (Savatier et al., 2002; Tichy and Stambrook, 2008). In response to DNA damage stress, cells generally slow or arrest cell cycle progression to repair or prevent the transmission of damage to daughter cells (Ishikawa et al., 2006). Cell cycle and DNA damage repair can be regulated during mES differentiation. During differentiation, mESCs accumulate in G1 phase and exhibit a cell cycle lengthened from 8–10 hr to more than 16 hr (White and Dalton, 2005). Additionally, DNA damage, especially DSB damage, is decreased during differentiation (Turinetto et al., 2012). Thus, there should be a system balancing the paradox of rapid proliferation and DNA damage repair to guarantee the normal self-renewal, pluripotency, and genomic stabilization in ESCs (Tichy, 2011). Here, we found that miR-590 balances DNA damage repair and proliferation by affecting the expression of Rad51b in mESCs. Importantly, Activin signaling regulated by Acvr2a mediates the balancing regulation of miR-590 on Rad51b. Furthermore, the miR-590/Acvr2a/Rad51b axis regulates the balance of rapid proliferation and DNA damage repair in mESCs.