GLI1 promotes cancer stemness through intracellular signaling pathway PI3K/Akt/NFκB in colorectal adenocarcinoma

Abstract

The role of Hedgehog (HH)/ glioma-associated oncogene homolog 1 (GLI1) pathway has been implicated in a variety of cancer entities, and the targeted pathway inhibition mediated by GLI1 is of therapeutic relevance. However, its oncogenicity and cross-talks with other cancer pathways including PI3K/Akt/NFκB, which modulates the HH/GLI1 signal strength, have rarely been explored in colorectal adenocarcinoma. We assessed the expression of GLI1 and its relationship with other cancer stemness genes, cell cycle markers, epithelial-mesenchymal transition (EMT), PI3K/Akt/NFκB signaling pathway genes, and HIF1α in 100 paraffin-embedded colorectal adenocarcinoma tissue samples using immunohistochemistry. We further addressed the effect of GLI1 on EMT, cell cycle, and its putative interaction with the PI3K/Akt/NFκB cascade in colorectal adenocarcinoma cell lines. The expression of GLI1 in colorectal adenocarcinoma tissues was found to correlate with the clinical stages, and distant metastasis. Moreover, GLI1 was found to be an independent predictor of poor overall survival and disease-free survival in colorectal adenocarcinoma. GLI1-expressing cancer cells also expressed their representative cancer stem-like cell (CSC) markers (SOX9 and CD133), as well as HIF1α. GLI1 expression was also strongly linked to EMT-related and PI3K/Akt/NFκB signaling genes. Downregulation of GLI1 by inhibitor treatment in colorectal adenocarcinoma cell lines resulted in reduced expression of CSC markers, cell clonogenicity, S-phase subpopulations, as well as the migration and invasion ability. Importantly, Akt inhibitor Perifosine significantly inhibited the expression of pAkt and GLI1 in colorectal adenocarcinoma cells. Combination of GLI1 inhibitor GANT61 and NFκB p65 inhibitor QZN exhibited much higher inhibition compared to using any of them individually on colorectal adenocarcinoma cells. We suggested that GLI1 may be a novel stem cell marker, and cancer stemness was activated via PI3K/Akt/NFκB pathway. In addition, co-targeting GLI1 and PI3K/Akt/NFκB signaling simultaneously might provide an alternative therapeutic strategy for colorectal adenocarcinoma patients.

Keywords: Colorectal adenocarcinoma; Epithelial-to-mesenchymal transition; Glioma-associated oncogene homolog 1; PI3K/Akt/NFκB pathway; Prognosis, cancer stem-like cell.