C-terminal sequences in R-Ras are involved in integrin regulation and in plasma membrane microdomain distribution.
The small GTPases R-Ras and H-Ras are highly homologous proteins with contrasting biological properties, for example, they differentially modulate integrin affinity: H-Ras suppresses integrin activation in fibroblasts whereas R-Ras can reverse this effect of H-Ras. To gain insight into the sequences directing this divergent phenotype, we investigated a panel of H-Ras/R-Ras chimeras and found that sequences in the R-Ras hypervariable C-terminal region including amino acids 175-203 are required for the R-Ras ability to increase integrin activation in CHO cells; however, the proline-rich site in this region, previously reported to bind the adaptor protein Nck, was not essential for this effect. In addition, we found that the GTPase TC21 behaved similarly to R-Ras. Because the C-termini of Ras proteins can control their subcellular localization, we compared the localization of H-Ras and R-Ras. In contrast to H-Ras, which migrates out of lipid rafts upon activation, we found that activated R-Ras remained localized to lipid rafts. However, functionally distinct H-Ras/R-Ras chimeras containing different C-terminal R-Ras segments localized to lipid rafts irrespective of their integrin phenotype.
Hansen
Malene
M
Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037, USA. maha@itsa.ucsf.edu
Prior
Ian A
IA
Hughes
Paul E
PE
Oertli
Beat
B
Chou
Fan-Li
FL
Willumsen
Berthe M
BM
Hancock
John F
JF
Ginsberg
Mark H
MH
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D002678:Chimera / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D020558:GTP Phosphohydrolases / Q000737:chemistry / Q000145:classification / Q000378:metabolism*; D006706:Homeostasis / Q000502:physiology; D016023:Integrins / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism*; D021962:Membrane Microdomains / Q000378:metabolism*; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D013045:Species Specificity; D013329:Structure-Activity Relationship; D018631:ras Proteins / Q000737:chemistry / Q000145:classification / Q000378:metabolism*
D016023:Integrins; D020558:GTP Phosphohydrolases; D018631:ras Proteins