Nucleolar protein treacle ribosome biogenesis factor 1 maintains gastric cancer cell proliferation by regulating R‐loop associated DNA replication stress

Gastric cancer (GC) is a common malignant neoplasm in the gastrointestinal tract, accounting for high mortality globally. Treacle ribosome biogenesis factor 1 (TCOF1) is a nucleolar protein, which has been reported to be implicated in the pathogenesis of Treacher Collins syndrome and the development of several types of human cancer. However, the role of TCOF1 in GC is not known.Immunohistochemistry was carried out to determine TCOF1 expression in GC tissues. Immunofluorescence, co-IP, and DNA fiber assays were conducted to investigate the function of TCOF1 in GC-derived BGC-823 and SGC-7901 cell lines.TCOF1 expression was aberrantly increased in GC tissues compared with adjacent normal tissues. In addition, we found that TCOF1 left the nucleolus and localized to R-loops (DNA/RNA hybrids) during S phase in GC cells. Furthermore, TCOF1 interacted with DDX5 and suppressed R-loop levels. Knockdown of TCOF1 led to increased nucleoplasmic R-loops specifically during S phase, which restrained DNA replication and cell proliferation. Overexpression of R-loop eraser RNaseH1 rescued the DNA synthesis defects and decreased DNA damage caused by TCOF1 depletion.These findings demonstrate a novel role of TCOF1 in maintaining GC cell proliferation by alleviating R-loop associated DNA replication stress.