The HRAS protein is a GTPase and is an early player in many signal transduction pathways and is usually associated with cell membranes due to the presence of an isoprenyl group on its C-terminus.

HRAS acts as a molecular on/off switch, once it is turned on it recruits and activates proteins necessary for the propagation of the receptor's signal, such as c-Raf and PI 3-kinase.

Subsequently, GTP present in the cytosol binds and HRAS-GTP dissociates from the GEF, resulting in HRAS activation.

The mutations responsible for Costello syndrome lead to the production of an HRAS protein that is permanently active.

Researchers are uncertain how mutations in the HRAS gene cause the other features of Costello syndrome (such as mental retardation, distinctive facial features, and heart problems), but many of the signs and symptoms probably result from cell overgrowth and abnormal cell HRAS has been shown to be a proto-oncogene.

Mutations in the HRAS gene also have been associated with the progression of bladder cancer and an increased risk of tumor recurrence after treatment.

DNA copy-number gain of a segment containing HRAS is included in a genome-wide pattern, which was found to be correlated with an astrocytoma patient's outcome.