Oncogenic K-ras segregates at spatially distinct plasma membrane signaling platforms according to its phosphorylation status.
Activating mutations in the K-Ras small GTPase are extensively found in human tumors. Although these mutations induce the generation of a constitutively GTP-loaded, active form of K-Ras, phosphorylation at Ser181 within the C-terminal hypervariable region can modulate oncogenic K-Ras function without affecting the in vitro affinity for its effector Raf-1. In striking contrast, K-Ras phosphorylated at Ser181 shows increased interaction in cells with the active form of Raf-1 and with p110α, the catalytic subunit of PI 3-kinase. Because the majority of phosphorylated K-Ras is located at the plasma membrane, different localization within this membrane according to the phosphorylation status was explored. Density-gradient fractionation of the plasma membrane in the absence of detergents showed segregation of K-Ras mutants that carry a phosphomimetic or unphosphorylatable serine residue (S181D or S181A, respectively). Moreover, statistical analysis of immunoelectron microscopy showed that both phosphorylation mutants form distinct nanoclusters that do not overlap. Finally, induction of oncogenic K-Ras phosphorylation - by activation of protein kinase C (PKC) - increased its co-clustering with the phosphomimetic K-Ras mutant, whereas (when PKC is inhibited) non-phosphorylated oncogenic K-Ras clusters with the non-phosphorylatable K-Ras mutant. Most interestingly, PI 3-kinase (p110α) was found in phosphorylated K-Ras nanoclusters but not in non-phosphorylated K-Ras nanoclusters. In conclusion, our data provide - for the first time - evidence that PKC-dependent phosphorylation of oncogenic K-Ras induced its segregation in spatially distinct nanoclusters at the plasma membrane that, in turn, favor activation of Raf-1 and PI 3-kinase.
Departament de Biologia Cel·lular, Immunologia i Neurociències, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Facultat de Medicina. Universitat de Barcelona, C/ Casanova 143, 08036 Barcelona, Spain.
Carles
C
Barceló
Noelia
N
Paco
Alison J
AJ
Beckett
Blanca
B
Alvarez-Moya
Eduard
E
Garrido
Mariona
M
Gelabert
Francesc
F
Tebar
Montserrat
M
Jaumot
Ian
I
Prior
Neus
N
Agell
D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D011905:Genes, ras; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D015398:Signal Transduction; D018631:ras Proteins / Q000235:genetics* / Q000378:metabolism*
D019869:Phosphatidylinositol 3-Kinases; D019908:Proto-Oncogene Proteins c-raf; D018631:ras Proteins
K-Ras; Nanoclusters; PI 3-kinase; PI3K; PKC; Phosphorylation; Raf