ROLE OF KLF6 TUMOR SUPPRESSOR IN COLON CANCER CELLS EXPRESSING MUTANT K-RAS AS ONCOGENIC DRIVER, UPON TREATMENT WITH PLK1 AND ROCK KINASES INHIBITORS

CASTELLARO A.; OCHOA D.; BOCCO J.L.

Mendoza

Congreso; SAIB-SAMIGE Joint Meeting 2021 ? Online; 2021

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Krüppel-like factor 6 (KLF6) belongs to a large family of mammalian Sp1-like/KLF transcription factors that play critical roles in regulating key cellular functions ranging from differentiation to proliferation and apoptosis. It has been described that KLF6 can fulfill an antitumor role causing the arrest of the cell cycle through the expression of p21(CIP1/WAF1). However, the arrest of the cell cycle caused by KLF6 decreases the cytotoxic effect produced by chemotherapeutic drugs that cause DNA damage. In this work, we analyze the role of KLF6 in cell death induced by treatment with drugs that inhibit PLK1 and ROCK kinases in HCT116 cells which express K-RasG13D mutant as an oncogenic driver. Mutational activation of the RAS family of genes is one of the most common oncogenic events in cancer, occurring in around 30% of human solid tumors. However, despite decades of study, effective therapies against tumors harboring RAS gain-of-function mutations remain a challenge since activated Ras is considered an undruggable target for cancer therapy. Hence, synthetic lethality approaches have begun to be explored to induce selective death in cells expressing activated Ras mutants. It was recently reported that the combined inhibition of PLK1 and ROCK kinases leads to potent induction of synthetic lethality in immortalized human ovarian epithelial cells expressing mutant K-Ras, but not in isogenic counterpart cells having K-Ras wt. The underlying mechanism involved apoptotic cell death through increased p21(CIP1/WAF1) expression. We observed that treatment with ROCK and PLK1 inhibitors (fasudil and volasertib, respectively) produced a peak of endogenous KLF6 expression levels at 6 h. after exposure of cells to these chemotherapy drugs. This increased KLF6 expression also occurred in response to fasudil alone, but not with volasertib as an individual treatment. The KLF6 responsiveness to both drugs was also analyzed in isogenic p53-/- cells where no significant differences were found with respect to HCT116 wt cells, both at the KLF6 expression levels and cell survival to fasudil treatment. This result indicates that cytotoxicity mediated by the mitotic stress caused by ROCK inhibition does not involve p53 function and opens a question about what does mean the KLF6 responsiveness to fasudil treatment. Remarkably, shRNA-mediated KLF6 downregulation renders HCT116 wt cells more sensitive to ROCK inhibition, and a similar effect was also found in HCT116 p21-/- cells. Hence, the tumor suppressor ability of KLF6 to interfere with oncogenesis triggered by mutant Ras, involving a p21(CIP1/WAF1)-mediated cell cycle arrest, must be inhibited to enhance the susceptibility to chemotherapy drugs based on mitotic stress, such as ROCK inhibition.