HBO1 promotes replication stress response through ATR-dependent phosphorylation of Ser50/53

Mounting evidence has shown that histone acetyltransferase binding to ORC1 (HBO1) serves as an oncoprotein, warranting the use of small molecule inhibitor WM-3835 for cancer therapy. However, HBO1 is ubiquitously expressed in both tumor and normal tissues, with potential to increase the risk of systematic toxicity. This unmet need highlights the importance of identifying suitable biomarkers to predict the sensitivity to HBO1 inhibitor. Here, we show that ATR, a key regulator of DNA replication stress, is a novel interacting partner of HBO1. Additionally, we reveal the regulatory function of HBO1 in DNA replication stress responses, in an ATR-dependent manner. Mechanistically, ATR mediated HBO1 Ser50/53 phosphorylation interferes with genomic binding of HBO1 and regulates gene expression. Notably, the overexpression of HBO1 mutated at the ATR phosphorylation site (S50/53A) dampens the expression of DNA repair related genes and suppresses tumor colony formation, consistent with the observations of WM-3835 treatment. Inhibition of ATR significantly antagonized the treatment sensitivity of WM-3835. Collectively, our findings uncovered a previously unidentified role of HBO1 in the regulation of replication stress and discovered ATR as a potential biomarker for WM-3835 treatment.