Ras homolog enriched in brain (Rheb) (Rheb)

Ras homolog enriched in brain (Rheb) is a small GTPase that serves as the essential proximal activator of the mechanistic target of rapamycin complex 1 (mTORC1), a central hub for regulating cell growth, protein synthesis, and autophagy (UniProt P36544). For Rheb to be biologically active, it must undergo a post-translational modification known as farnesylation, where a 15-carbon farnesyl lipid group is attached to its C-terminal CAAX motif by the enzyme farnesyltransferase (PubMed: 15545991). This modification is crucial for anchoring Rheb to the lysosomal membrane, the site where it interacts with and activates mTORC1. In pathological states such as Tuberous Sclerosis Complex (TSC) and certain cancers, the loss of the TSC1/TSC2 complex leads to an accumulation of Rheb in its active GTP-bound state, causing constitutive mTORC1 signaling and uncontrolled cellular proliferation (PubMed: 12665855). Targeting Rheb farnesylation has emerged as a potent therapeutic strategy, particularly through the use of farnesyltransferase inhibitors (FTIs) like tipifarnib and lonafarnib. By blocking the farnesylation of Rheb, these drugs prevent its membrane localization, effectively sequestering it from mTORC1 and inhibiting downstream signaling (PubMed: 33009416). This approach is being investigated for patients with TSC-mutant tumors and other malignancies where mTORC1 is hyperactivated. Clinical challenges include managing the off-target effects of FTIs, as they also inhibit the farnesylation of other proteins, and identifying the specific patient populations most likely to benefit from this intervention.

Other names

Rheb1Ras homolog enriched in brain 1RHEB1Ras homolog enriched in brain

Farnesyltransferase inhibitors (FTIs) block the post-translational attachment of a farnesyl group to the Rheb CAAX motif, preventing its localization to the lysosomal membrane and subsequent activation of mTORC1.