Suppression of Super-Enhancer Activity Associated with c-Myc Gene in Pancreatic Cancer Cells
Super-enhancers (SEs) are large clusters of transcriptional enhancers that recruit multiple transcription factors and co-activators to augment transcription. Many oncogenes, including c-Myc, are associated with SEs in cancer cells and hence play important roles in tumor initiation and growth. In this study, we used the CRISPR interference (CRISPRi) to suppress the SE activity associated with the c-Myc genes in pancreatic cancer cells. The CRISPR (clustered, regularly interspaced, short palindromic repeats)-Cas9 system is a gene editing tool that allows for highly specific altering of DNA sequences and modifies gene function. Using a nuclease-inactive dCas9 linked to the Krüppel-associated box (KRAB) repressor (dCas9-KRAB), expression can be suppressed on a target gene sequence that is complementary to the sgRNA (short guide RNA). Here, we used CRISPRi-dCas9-KRAB vectors with sgRNA sequences that are complementary to the SE region of the c-Myc gene to suppress the binding of transcription factors and co-activators to the SE region and consequently, decrease c-Myc expression. The sgRNA sequences were inserted into the vectors and transfected into pancreatic cancer cells (MIA PaCa-2 and PSN1) using lipofectamine. Cells were harvested 72 hours after transfection and the c-Myc expression in the cells was examined at both mRNA and protein levels using RT-PCR and Western blotting, respectively. We observed that in PSN1 cells, all sgRNA sequences caused a decrease in c-Myc protein level compared to the control. This result indicates that suppression of SE activity using CRISPRi can reduce the expression of c-Myc in PDAC cells.