Browsing by Author "Brodkin, Jefim"

Colorectal cancer (CRC) is the third most common cancer in the world. About 68% of all colorectal cancer patients are alive five years after diagnosis. About half of all cancer patients receive radiation therapy. Ionizing radiation causes DNA damage to cells, which leads to cell death if unrepaired. Although radiation is an effective cancer treatment, some tumor cells – especially cancer stem cells – are resistant to radiation-induced DNA damage, which allows them to survive radiation therapy. Disruption of the Wnt/β-catenin signaling pathway, which occurs in almost all CRC patients, leads to overactivation of the PROX1 gene. PROX1 has been found to promote dysplastic changes and an invasive phenotype of CRC. Since PROX1 has been shown to be expressed in cancer stem cells, our hypothesis was that PROX1 expression protects tumor cells from radiation-induced damage. We found that PROX1 expression promotes radiation resistance in colorectal cancer cells. First, we found that irradiation itself increases the proportion of PROX1-expressing cells. Furthermore, we found that cells overexpressing PROX1 endure radiation better than PROX1-negative cells. To elucidate the underlying mechanisms of radiation resistance, we performed single-cell RNA sequencing to CRC patient organoid cultures and to adenoma cells isolated from ApcMin/+ tumor-bearing mice. The data showed enhanced expression of multiple DNA damage repair transcripts in PROX1-positive cells. In addition, we showed that following irradiation, PROX1-expressing cells had less DNA damage. Furthermore, we showed that DNA damage repair occured faster in PROX1-positive cells, especially through non- homologous end joining (NHEJ), than in PROX1-negative cells, and that inhibition of NHEJ decreased the survival of PROX1-positive cells following irradiation. Our data showed that PROX1 has a protective effect on tumor stem cells and promotes radiation resistance, which may be a possible druggable target in the future.