An Essential Role for MCL-1 in ATR-mediated CHK1 Phosphorylation

Abstract

INTRODUCTIONMyeloid cell leukemia 1 (Mcl-1) was first identified as a gene induced during myeloid cell differentiation (Kozopas et al., 1993) and is a prosurvival member of the Bcl-2 family. The activity of Bcl-2 family proteins involves several Bcl-2 homology (BH) domains (Danial and Korsmeyer, 2004) that control protein-protein interactions. These proteins play an important role in cancer by regulating cell death and survival. Compared with other prosurvival members such as Bcl-2 or Bcl-xL, Mcl-1 has been shown to have more transient survival effects (Zhou et al., 1997). Unlike other members of the family, the half-life of Mcl-1 is very short and its expression is highly regulated by growth factors and a variety of other agents. Moreover, Mcl-1 has an extended N-terminus that is not conserved in any other Bcl-2 family protein. The N-terminus contains two PEST domains, which are found in proteins that are rapidly turned over, but deletion of the PEST domains does not extend the short half-life of Mcl-1 (Akgul et al., 2000;Clohessy et al., 2004). When the Mcl-1 gene was knocked out in a mouse model, it resulted in peri-implantation lethality (Rinkenberger et al., 2000), but Mcl-1Ϫ/Ϫ embryos showed no alterations in the extent of apoptosis, indicating that Mcl-1 plays a role early in development distinct from its prosurvival functions. We and others reported that Mcl-1 expression can lead to suppression of cell proliferation and may have effects on cell cycle machinery (Fujise et al., 2000;Jamil et al., 2005). We showed that a short nuclear form of Mcl-1 (snMcl-1) was associated primarily with the inactive form of Cdk-1 in the nucleus, most prominently during the G2 phase of the cell cycle, which suggested a potential means by which Mcl-1 mediates its anti-proliferative effects (Jamil et al., 2005).It is now well established that genome surveillance mechanisms function to cause a delay, or arrest, in progression of the cell cycle at the boundary of G1/S or G2/M in response to DNA damage (Zhou and Elledge, 2000;Abraham, 2001;Kastan, 2001;Nyberg et al., 2002;Sancar et al., 2004). These surveillance mechanisms are known to involve a network of interacting proteins that recognize damage and elicit responses including cell cycle delay, DNA repair, and apoptosis (Elledge, 1996;Zhou and Elledge, 2000). Cdk's, which play a central role in cell cycle progression, are key targets of these checkpoints (Iliakis et al., 2003 MATERIALS AND METHODS Cell LinesHeLa, HL-60, and FDC-P1 cells were obtained from ATCC (Manassas, VA). ATM-deficient HT-144 cells were a kind gift from Dr. P. Olive (BC Cancer Agency). ATR-defective fibroblasts, F02-98, were a kind gift from Dr. P. Jeggo. Hs68, which are primary human foreskin fibroblasts (Wheaton and Riabowol, 2004), maintained within 30 -60 mean population doublings, were kindly provided by Dr. K. Riabowol (University of Calgary). HL-60 cells were cultured in RPMI1640 supplemented with 10% fetal bovine serum (FBS), 1 mM sodium pyruvate, 2 mM l-glutamine. FDC-P1 cells were grown in RPMI...

STAT3 and MCL-1 associate to cause a mesenchymal epithelial transition

“…6C). This correlates with earlier reports that transient transfection with MCL-1 increases the expression of phosphoSer345 Chk1 in the absence of DNA damage and leading to accumulation of cells in G2 (Jamil et al, 2008), which suggests a new role for MCL-1 in generating an appropriate response to DNA damage and in the maintenance of chromosome integrity (Jamil et al, 2008).…”

Human FEM1B is required for Rad9 recruitment and CHK1 activation in response to replication stress

“…In spite of these findings, Claspin ablation in HeLa cells did not impede CHK1 activation and only minimally affected the later phase of CHK1 phosphorylation (Chini et al, 2006), suggesting that an alternative pathway does exist. In addition to our findings with FEM1B, a recent study implicated the involvement of another protein, MCL-1, a Bcl-2 family member, in the activation of CHK1 by DNA damage (Jamil et al, 2008). Overexpression of MCL-1 causes CHK1 phosphorylation at activating sites, whereas knockdown abolished it (Jamil et al, 2008).…”

“…In addition to our findings with FEM1B, a recent study implicated the involvement of another protein, MCL-1, a Bcl-2 family member, in the activation of CHK1 by DNA damage (Jamil et al, 2008). Overexpression of MCL-1 causes CHK1 phosphorylation at activating sites, whereas knockdown abolished it (Jamil et al, 2008). How this is accomplished is unknown except that MCL-1 also interacts with activated CHK1 in damagetreated cells.…”

Growth inhibitory effect and Chk1-dependent signaling involved in G2/M arrest on human gastric cancer cells induced by diallyl disulfide

“…ATR mediates checkpoint signaling through its downstream effect or Chk1 (20). As shown in Figure 6, treatment of BCC823 cells for 15 min to 2 h resulted in an increase in phospho-ATR expression, whereas no change was found in ATR expression.…”