NRAS is unique among RAS proteins in requiring ICMT for trafficking to the plasma membrane

Abstract

Isoprenylcysteine carboxyl methyltransferase (ICMT) is the third of three enzymes that sequentially modify the C-terminus of CaaX proteins, including RAS. Although all four RAS proteins are substrates for ICMT, each traffics to membranes differently by virtue of their hypervariable regions that are differentially palmitoylated. We found that among RAS proteins, NRAS was unique in requiring ICMT for delivery to the PM, a consequence of having only a single palmitoylation site as its secondary affinity module. Although not absolutely required for palmitoylation, acylation was diminished in the absence of ICMT. Photoactivation and FRAP of GFP-NRAS revealed increase flux at the Golgi, independent of palmitoylation, in the absence of ICMT. Association of NRAS with the prenyl-protein chaperone PDE6δ also required ICMT and promoted anterograde trafficking from the Golgi. We conclude that carboxyl methylation of NRAS is required for efficient palmitoylation, PDE6δ binding, and homeostatic flux through the Golgi, processes that direct delivery to the plasma membrane.

Specific Disruption of Ras2 CAAX Proteolysis Alters Its Localization and Function

“…While palmitoylation of different Ras isoforms is traditionally thought to require prior prenylation, palmitoylation has been detected in the absence of prenylation or full CAAX processing ( 21 , 26 – 28 ). We directly investigated this issue for Ras2 using the acyl-polyethylene glycol (PEG) exchange (APE) assay, which has been applied for investigations of mammalian Ras palmitoylation ( 29 ).…”

Pathway-based Approach Reveals Differential Sensitivity to E2F1 Inhibition in Glioblastoma

“…Additionally, T2-1P (PIK3R1 and EBF1 activated) significantly associated with adult astrocytic markers and the AC-like molecular state, and T2-2N (ICMT activated) significantly associated with adult OPC markers and both OPC-like and NPC1-like molecular states. Notably, ICMT is a methyl transferase necessary for the localization of CaaX proteins (which include the Ras family) to the cell membrane (38,39). Ras/ERK signaling has been associated with the proneural subtype (40) and NRAS is expressed at higher levels in proneural subtype compared with mesenchymal and classical (https://gliovis.bioinfo.cnio.es/).…”

Drugging the Undruggable: Advances on RAS Targeting in Cancer

“…In parallel, efforts to inhibit KRAS post-translational modifications have moved to target the downstream processing enzymes, RCE1 and ICMT [21,22]. Recent data show that NRAS is strongly dependent on ICMT activity for efficient trafficking, which would suggest that ICMT inhibitors could be a good therapeutic strategy for NRAS-driven tumours [23]. Another potential target that has been recently identified is the prenyl-binding protein phosphodiesterase δ (PDEδ), which regulates RAS localisation and trafficking [24].…”