Abstract 2137 Evaluating the effect of RNAi silencing on the KRAS translocation in pancreatic Cancer Cells

Membrane-bound Ras proteins are small GTPases involved in the activation of cell proliferation and differentiation. Several Ras family members have been implicated in cancer cells, with mutations in the KRAS gene being the most prevalent. K-Ras is regulated by guanine nucleotide exchange factors (GEF) in the Map kinase cascade. K-Ras is translocated from the endoplasmic reticulum to the plasma membrane via the attraction of a basic hypervariable domain to acidic lipid rafts. This docking allows for recruitment and activation of the Map Kinase Cascade. The end goal of this cascade is activation of transcription factors which enhance proliferation and cell migration. Most cancerous cell lines have a mutation in the KRAS pathway, resulting in increased cell motility and growth. 40% of pancreatic cancer cases have KRAS mutations and current KRAS inhibitors have not been shown to have consistent impact in patients. RNAi is a regulatory mechanism in eukaryotic cells that uses double stranded RNA as a regulation of gene expression. In drug resistant cancers, studies have shown RNA interference in the KRAS signaling pathway can have a significant therapeutic effect. Small interfering RNA loads onto enzymatic machinery and targets homologous sequences in mRNA transcripts for degradation leading to loss of protein expression in RNAi treated cells. K-Ras C-terminal membrane anchor binds to the lipid phosphatidylserine (PtdSer), a negatively charged phospholipid in the plasma membrane. Loss of PtdSer prevents K-Ras association during translocation (from lysine (basic) rich HVR) thus inhibiting K-Ras signaling. Phosphatidylserine synthase (PTDSS1) is responsible for production of phosphatidylserine and presents a novel target for RNA interference. We evaluated the effect on mRNA levels and cell viability after RNA interference of PTDSS1 in PANC-1 pancreatic cancer cells.