A CRISPR-Cas9 repressor for epigenetic silencing of KRAS.

KRAS is one of the most frequently mutated oncogenes in cancers. Currently no direct and effective anti-KRAS therapies are available. Using the powerful CRISPR-Cas9 technology to target the mutant KRAS promoter, we designed an epigenetic repressor to silence KRAS through epigenome editing. Catalytically dead Cas9 (dCas9) functioned as a DNA binding device, which was fused with a transcriptional repressor histone deacetylase 1 (HDAC1). We designed a panel of three CRISPR RNAs (crRNAs) covering 1500-bp range of the KRAS promoter and identified that crRNA1 and crRNA2 efficiently silenced KRAS. The suppression of K-Ras resulted in a significant inhibition of cell growth, suppression of colony formation in soft agar and induction of cell death in cancer cells with KRAS mutations. In addition, the chromatin immunoprecipitation (ChIP) assay demonstrated dCas9-HDAC1 modified histone acetylation on the KRAS promoter. Furthermore, transfection of dCas9-HDAC1 protein and gRNA ribonucleoprotein complex also inhibited K-Ras and suppressed cell proliferation. In summary, we have developed a new strategy that combines CRISPR-Cas9 technology with HDAC1 epigenetic silencing to target cancers driven by KRAS mutations.