Brg1 is required to maintain colorectal cancer stem cells

Abstract

Tumor cells capable of self-renewal and continuous production of progeny cells are called tumor stem cells (TSCs) and are considered to be potential therapeutic targets. However, the mechanisms underlying the survival and function of TSCs are not fully understood. We previously reported that chromatin remodeling regulator Brg1 is essential for intestinal stem cells in mice and Dclk1 is an intestinal TSC marker. In this study, we investigated the role of Brg1 in Dclk1 + intestinal tumor cells for the maintenance of intestinal tumors in mice. Specific ablation of Brg1 in Dclk1 + intestinal tumor cells reduced intestinal tumors in Apc Min mice, and continuous ablation of Brg1 maintained the reduction of intestinal tumors. Lineage tracing in the context of Brg1 ablation in Dclk1 + intestinal tumor cells revealed that Brg1-null Dclk1 + intestinal tumor cells did not give rise to their descendent tumor cells, indicating that Brg1 is essential for the self-renewal of Dclk1 + intestinal tumor cells. Five days after Brg1 ablation, we observed increased apoptosis in Dclk1 + tumor cells. Furthermore, Brg1 was crucial for the stemness of intestinal tumor cells in a spheroid culture system. BRG1 knockdown also impaired cell proliferation and increased apoptosis in human colorectal cancer (CRC) cells. Microarray analysis revealed that apoptosis-related genes were upregulated and stem cell-related genes were downregulated in human CRC cells by BRG1 suppression. Consistently, high BRG1 expression correlated with poor disease-specific survival in human CRC patients. These data indicate that Brg1 plays a crucial role in intestinal TSCs in mice by inhibiting apoptosis and is critical for cell survival and stem cell features in human CRC cells. Thus, BRG1 represents a new therapeutic target for human CRC.

JNK pathway plays a critical role for expansion of human colorectal cancer in the context of BRG1 suppression

“… 16 Of the 50 most upregulated genes in BRG1 ‐silenced hCRC cells, we observed JUN ( c‐JUN ) and MAP3K14 , which were known to be JNK pathway‐related genes, and DDIT3 ( CHOP ) and HMOX1 , which were known to be ER stress‐related genes. 16 Gene Set Enrichment Analysis revealed that there was a positive enrichment of gene sets related to the JNK pathway (“ST_JNK_MAPK_PATHWAY”) in BRG1 ‐silenced cells (Figure 1D ). These findings indicate that the JNK pathway was upregulated in the context of BRG1 suppression in hCRC cells.…”

“…Our recent work indicated that the expression of BRG1 is suppressed by siRNA technique at nearly 10% in hCRC cells (DLD‐1 and HCT 116) and that BRG1 silencing results in impaired cell growth, loss of stemness feature, and increased apoptosis in hCRC cells. 16 In the report, we undertook a microarray analysis of control and BRG1 ‐silenced hCRC cells (GSE 169627). The heatmap showed that expression of the JNK pathway genes was upregulated in BRG1 ‐silenced DLD‐1 and HCT 116 cells (Figure 1C ).…”

“… 14 Previous reports, including our report, have shown that hCRCs strongly express BRG1. 12 , 15 , 16 As in other types of cancer, expression of BRG1 in hCRC is associated with recurrence, metastasis, and poor prognosis. 12 , 13 , 16 We have recently reported that Brg1 plays an essential role for maintenance of murine intestinal TSCs and for cell survival and stemness features of hCRC cells.…”

“… 12 , 15 , 16 As in other types of cancer, expression of BRG1 in hCRC is associated with recurrence, metastasis, and poor prognosis. 12 , 13 , 16 We have recently reported that Brg1 plays an essential role for maintenance of murine intestinal TSCs and for cell survival and stemness features of hCRC cells. 16 Continuous ablation of Brg1 in intestinal TSCs maintains suppression of intestinal tumors accompanied by increased apoptosis and loss of their capacity for self‐renewal in mice.…”

“… 12 , 13 , 16 We have recently reported that Brg1 plays an essential role for maintenance of murine intestinal TSCs and for cell survival and stemness features of hCRC cells. 16 Continuous ablation of Brg1 in intestinal TSCs maintains suppression of intestinal tumors accompanied by increased apoptosis and loss of their capacity for self‐renewal in mice. However, it is still unclear how BRG1 suppression changes the underlying intracellular mechanisms of hCRC cells.…”