High affinity for farnesyltransferase and alternative prenylation contribute individually to K-Ras4B resistance to farnesyltransferase inhibitors.
Farnesyltransferase inhibitors (FTIs) block Ras farnesylation, subcellular localization and activity, and inhibit the growth of Ras-transformed cells. Although FTIs are ineffective against K-Ras4B, the Ras isoform most commonly mutated in human cancers, they can inhibit the growth of tumors containing oncogenic K-Ras4B, implicating other farnesylated proteins or suggesting distinct functions for farnesylated and for geranylgeranylated K-Ras, which is generated when farnesyltransferase is inhibited. In addition to bypassing FTI blockade through geranylgeranylation, K-Ras4B resistance to FTIs may also result from its higher affinity for farnesyltransferase. Using chimeric Ras proteins containing all combinations of Ras background, CAAX motif, and K-Ras polybasic domain, we show that either a polybasic domain or an alternatively prenylated CAAX renders Ras prenylation, Ras-induced Elk-1 activation, and anchorage-independent cell growth FTI-resistant. The polybasic domain alone increases the affinity of Ras for farnesyltransferase, implying independent roles for each K-Ras4B sequence element in FTI resistance. Using microarray analysis and colony formation assays, we confirm that K-Ras function is independent of the identity of the prenyl group and, therefore, that FTI inhibition of K-Ras transformed cells is likely to be independent of K-Ras inhibition. Our results imply that relevant FTI targets will lack both polybasic and potentially geranylgeranylated methionine-CAAX motifs.
Fiordalisi
James J
JJ
Department of Radiation Oncology and Pharmacology, CB #7512, University of North Carolina, Chapel Hill, NC 27599-7512, USA. fiordali@med.unc.edu
Johnson
Ronald L
RL
Weinbaum
Carolyn A
CA
Sakabe
Kaoru
K
Chen
Zhui
Z
Casey
Patrick J
PJ
Cox
Adrienne D
AD
D016475:3T3 Cells; D019883:Alkyl and Aryl Transferases / Q000037:antagonists & inhibitors*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002455:Cell Division; D004268:DNA-Binding Proteins; D004351:Drug Resistance / Q000235:genetics*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051231:Farnesyltranstransferase; D020869:Gene Expression Profiling; D006801:Humans; D051379:Mice; D009154:Mutation; D017368:Protein Prenylation / Q000502:physiology*; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection; D050807:ets-Domain Protein Elk-1; D018631:ras Proteins / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*
D004268:DNA-Binding Proteins; C494112:ELK1 protein, human; C494113:Elk1 protein, mouse; D004791:Enzyme Inhibitors; C117307:KRAS protein, human; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D019883:Alkyl and Aryl Transferases; D051231:Farnesyltranstransferase; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins