RACK1 regulates Ki-Ras-mediated signaling and morphological transformation of NIH 3T3 cells.
Activating Ras mutations are involved in a significant fraction of human tumors. A suppressor screen using a retroviral mouse fibroblast cDNA library was performed to identify novel factors in Ras-mediated transformation. We identified a novel potent inhibitor of Ras-mediated morphological transformation encoded by a truncated version of the receptor for activated C-kinase (RACK1). The truncated protein, designated RACK1DeltaWD1, lacked the N-terminal 49 amino acids encoding the first of the 7 WD40 repeats in RACK1. RACK1DeltaWD1 expression restored contact inhibition, stress fiber formation and reduced ERK phosphorylation in Ki-Ras transformed NIH 3T3 cells. We demonstrate that truncated RACK1 is involved in complexes consisting of wild-type RACK1 and protein kinase C isoforms alpha, betaI and delta, compromising the transduction of an activated Ras signal to the Raf-MEK-ERK pathway. The cellular localization of RACK1DeltaWD1 differed from wtRACK1, indicating that signaling complexes containing the truncated version of RACK1 are incorrectly localized. Notably, 12-O-tetradecanoyl-13-phorbol acetate (TPA) mediated intracellular translocation of RACK1-interacting PKC alpha and delta was abrogated in RACK1DeltaWD1-expressing cells. Our data support a model where RACK1 acts as a key factor in Ki-Ras-mediated morphological transformation.
Bjørndal
Bodil
B
Department of Molecular Biology, University of Bergen, Bergen, Norway.
Myklebust
Line M
LM
Rosendal
Ken Roger
KR
Myromslien
Frøydis D
FD
Lorens
James B
JB
Nolan
Garry
G
Bruland
Ove
O
Lillehaug
Johan R
JR
D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D015723:Gene Library; D051379:Mice; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D009479:Neuropeptides / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D011493:Protein Kinase C / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism*; D000075370:Receptors for Activated C Kinase; D017384:Sequence Deletion; D015398:Signal Transduction; D025521:Tumor Suppressor Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*
D000199:Actins; D009479:Neuropeptides; C090294:RACK1 protein, mouse; D000075370:Receptors for Activated C Kinase; D025521:Tumor Suppressor Proteins; D011493:Protein Kinase C; D048049:Extracellular Signal-Regulated MAP Kinases; D016283:Proto-Oncogene Proteins p21(ras)