No abstract

The G2/M checkpoint is activated on DNA damage by the ATM and ATR kinases that are regulated by post-translational modifications. In this paper, the transcriptional coregulation of ATM and ATR by SMARCAL1 and BRG1, both members of the ATPdependent chromatin remodeling protein family, is described. SMARCAL1 and BRG1 colocalize on the promoters of ATM and ATR; downregulation of SMARCAL1/BRG1 results in transcriptional repression of ATM/ATR and therefore, overriding of the G2/M checkpoint leading to mitotic abnormalities. On doxorubicin-induced DNA damage, SMARCAL1 and BRG1 are upregulated and in turn, upregulate the expression of ATM/ATR. Phosphorylation of ATM/ATR is needed for the transcriptional upregulation of SMARCAL1 and BRG1, and therefore, of ATM and ATR on DNA damage. The regulation of ATM/ATR is rendered non-functional if SMARCAL1 and/or BRG1 are absent or if the two proteins are mutated such that they are unable to hydrolyze ATP, as in for example in Schimke Immuno-Osseous Dysplasia and Coffin-Siris Syndrome. Thus, an intricate transcriptional regulation of DNA damage response genes mediated by SMARCAL1 and BRG1 is present in mammalian cells.

The G2/M checkpoint is activated on DNA damage by the ATM and ATR kinases that are regulated by post-translational modifications. In this paper, the transcriptional coregulation of ATM and ATR by SMARCAL1 and BRG1, both members of the ATPdependent chromatin remodeling protein family, is described. SMARCAL1 and BRG1 colocalize on the promoters of ATM and ATR; downregulation of SMARCAL1/BRG1 results in transcriptional repression of ATM/ATR and therefore, overriding of the G2/M checkpoint leading to mitotic abnormalities. On doxorubicin-induced DNA damage, SMARCAL1 and BRG1 are upregulated and in turn, upregulate the expression of ATM/ATR. Phosphorylation of ATM/ATR is needed for the transcriptional upregulation of SMARCAL1 and BRG1, and therefore, of ATM and ATR on DNA damage. The regulation of ATM/ATR is rendered non-functional if SMARCAL1 and/or BRG1 are absent or if the two proteins are mutated such that they are unable to hydrolyze ATP, as in for example in Schimke Immuno-Osseous Dysplasia and Coffin-Siris Syndrome. Thus, an intricate transcriptional regulation of DNA damage response genes mediated by SMARCAL1 and BRG1 is present in mammalian cells.

ATP-dependent chromatin remodeling proteins use the energy released from ATP hydrolysis to reposition nucleosomes in DNA-dependent processes. These proteins are classified as SF2 helicases. SMARCAL1, a member of this protein family, is known to modulate both DNA repair and transcription by specifically recognizing DNA molecules possessing double-strand to single-strand transition regions. Mutations in this gene cause a rare autosomal recessive disorder known as Schimke Immuno-Osseous Dysplasia (SIOD).Structural studies have shown that the ATP-dependent chromatin remodeling proteins possess two RecA-like domains termed as RecA-like domain 1 and RecA-like domain 2. Using Active DNA-dependent ATPase A domain (ADAAD), the bovine homolog of SMARCAL1, as a model system we had previously shown that the RecA-like domain 1 containing helicase motifs Q, I, Ia, II, and III are sufficient for ligand binding; however, the Rec A-like domain 2 containing motifs IV, V, and VI are needed for ATP hydrolysis. In the present study, we have focused on the motifs present in the RecA-like domain 2. Our studies demonstrate that the presence of an aromatic residue in motif IV is needed for interaction with DNA in the presence of ATP. We also show that the motif V is required for the catalytic efficiency of the protein and motif VI is needed for interaction with DNA in the presence of ATP. Finally, we show that the SIOD-associated mutation, R820H, present in motif VI results in loss of ATPase activity, and therefore, reduced response to DNA damage.