Immunocytochemical assay for Ras activity

Abstract

This chapter describes the immunocytochemical assay for Ras activity. These activating ras mutations cause loss of intrinsic Ras guanosine triphosphate (GTPase) activity or an increased rate of guanine nucleotide exchange, both resulting in a higher proportion of active (GTP-bound) Ras. Mutations in ras genes that result in constitutively high Ras activity are likely to be early events in the progression of numerous cancers. Alterations in Ras mediators can also result in elevated Ras activity in affected cells. At present, efforts are focused on developing reverse transcription- polymerase chain reaction (RT-PCR) techniques that identify activating ras mutations in tissues and other samples. While these assays may have predictive diagnostic and prognostic value, they do not measure Ras activity and cannot be used to identify which cells in a sample are affected. More importantly, these assays fail to identify cells with elevated Ras activity because of increased Ras expression or mutations in Ras mediators.