BRAF V600E-induced distinct DNA damage response defines the therapeutic potential of p53 activation for TP53 wild-type colorectal cancer.

ABSTRACT

BRAF V600E, one of the most frequent mutations in the MAPK pathway, confers poor prognosis to colorectal cancers (CRCs), partly because of chemotherapeutic resistance. Oncogene-induced DNA damage responses (DDRs) that primarily activate p53 are important mechanistic barriers to the malignant transformation of cells; however, the mechanism underlying this impairment in cancer remains unknown. Here, we evaluated the responses of BRAFV600E-induced DDRs in two CRC cell lines, SW48 and LIM1215, both of which harbor wild-type TP53, KRAS, and BRAF. BRAFV600E transduction exhibited distinct phenotypes in these cells SW48 cell proliferation markedly decreased, whereas that of LIM1215 increased. BRAFV600E expression induced the activation of oncogene-induced DDR signaling in SW48 cells, but not in LIM1215 cells, whereas chemotherapeutic agents similarly activated DDRs in both cell lines. Knockdown experiments revealed that these responses in SW48 cells were mediated by p53-p21 pathway activation. Comet assay (both alkaline and neutral) revealed that BRAFV600E increased single-strand breaks to the same extent in both cell lines; however, in case of LIM1215 cells, it only facilitated double-strand breaks. Furthermore, the proliferation of LIM1215 cells, wherein no oncogene-induced DDRs occurred, was synergistically inhibited upon MDM2 inhibitor-mediated p53 activation combined with MEK inhibition. Taken together, these distinct DDR signaling responses highlight the novel characteristics of BRAFV600E-mutated CRC cells and define the therapeutic potential of p53 activation combined with MAPK inhibition against TP53 wild-type CRC harboring a BRAFV600E mutation.