ChIP-Seq landscapes of BCL6 and STAT5 transcription factors in DLD-1 colorectal cancer cells

Colorectal cancer is one of the most prevalent types of cancer worldwide and the GTPase RAC1 and its effector PAK1 have been found overexpressed or hyperactivated in colorectal cancers, particularly those with more aggressive and invasive features, leading to unfavorable clinical prognosis, often resulting from chemoresistance. Previously, we described a new signaling pathway in which activation of RAC1/PAK1 signaling promotes a transcriptional switch between the BCL6 repressor and the STAT5 transcriptional activator, leading to increased expression of a subset of cell-cycle genes. Here we used an innovative ChIP-Seq data analysis approach, using biological rather than statistical filters, for the genome wide identification of the BCL6/STAT5 switch target genes. Enrichment analysis among the 1834 identified target genes revealed an overrepresented cluster of 30 genes involved in DNA damage repair. Combining protein network analysis with read count data, we identified the pivotal genes in this cluster and demonstrated that their expression in DLD-1 colorectal cancer cells increased in response to the stimulation of RAC1/PAK1 signaling. Moreover, using the comet assay as a read out of the extent of DNA damage, we show that the activation of this pathway provides partial protection against damage induced by alkylating agents and significantly accelerates DNA damage repair. This work demonstrates a role for the RAC1/PAK1-BCL6/STAT5 pathway in enhancing DNA damage repair mechanisms that may contribute for the chemoresistant phenotype of aggressive colorectal tumors.