Ras and Its Signals Diffuse through the Cell on Randomly Moving Nanoparticles

Abstract

Spatiotemporal modulation of Ras signaling from different intracellular compartments requires mechanisms allowing Ras and its signals to navigate across cells. Here, we describe one mechanism by which clusters of palmitoylated H-Ras and N-Ras isoforms but not nonpalmitoylated K-Ras diffuse through the cytoplasm, independently of ATP, on fast, randomly moving, small cytosolic nanoparticles (''rasosomes''). Rasosomes forced to diffuse out of live cells and trapped by Ras antibody beads appear as round structures of 80-to 100-nm diameter. Association of H-Ras with rasosomes requires Ras palmitoylation and the hypervariable sequence (hvr) upstream of the palmitoylated cysteines. H-Ras hvr mutants that fail to interact with rasosomes are biologically inactive. Epidermal growth factor stimulation rapidly increases active H-Ras-GTP and phosphorylated extracellular signal-regulated kinase (ERK) on rasosomes. Similarly, rasosomes carrying H-Ras(G12V) but not H-Ras are loaded with active ERK. Thus, the rasosome represents a hitherto unknown particle that enables Ras signal information to spread rapidly across cells. (Cancer Res 2006; 66(4): 1974-81)

Tumor Cells Secrete Galectin-1 to Enhance Endothelial Cell Activity

“…GTP nanoclusters or rasosomes that are found at the plasma membrane and that occur as small, randomly moving cytoplasmic particles (24,25). This also corroborates with previous observations that the galectin-1-binding angiostatic peptide anginex is taken up by endothelial cells and colocalizes with galectin-1 in dot-like vesicles (7).…”

“…In line with this, our data show increased phosphorylation of Raf, Mek, and Erk in endothelial cells after treatment with exogenous galectin-1. Moreover, the absorbed galectin-1 appeared in small dot-like particles, resembling the H-Ras.GTP nanoclusters or rasosomes, which are found at the plasma membrane and occur as small, randomly moving cytoplasmic particles (24,25). This also corroborates with our previous observations that the galectin-1-binding angiostatic peptide anginex is also taken up by endothelial cells and colocalizes with galectin-1 in dot-like vesicles (7).…”

Palmitoylation and localisation of RAS isoforms are modulated by the hypervariable linker domain

“…Most simply, the linker domain might stabilise insertion of the palmitoyl group into membranes, allowing N-RAS to be sorted more efficiently into plasma-membrane-directed vesicles (so-called 'rasosomes') (Rotblat et al, 2006). This would be analogous to the effect of the second H-RAS palmitoyl group, which is sufficient to allow plasma membrane targeting in the absence of a linker domain.…”

A Unique Platform for H-Ras Signaling Involving Clathrin-independent Endocytosis

“…Phosphorylation of K-Ras causes it to translocate to mitochondria where it is involved in mediating apoptosis (Bivona et al, 2006). Finally, Ras can generate signals from other compartments such as rasosomes (Rotblat et al, 2006) and endosomes (Rizzo et al, 2001;Jiang and Sorkin, 2002;Roy et al, 2002).…”