title: Inhibition of DNA synthesis by a farnesyltransferase inhibitor involves inhibition of the p70(s6k) pathway.
abstract: Previously, the protein farnesyltransferase inhibitor (FTI), L-744, 832, has been shown to inhibit the proliferation of a number of tumor cell lines in vitro in a manner that correlated with the inhibition of the mitogen-activated protein kinase cascade. Here we show that FTI inhibits p70(s6k) phosphorylation in mammary tumors in vivo in transgenic mice. Furthermore, in a mouse keratinocyte cell line, FTI inhibits p70(s6k) phosphorylation and activity and inhibits PHAS-1 phosphorylation in vitro in both rapidly growing cells and in growth factor-stimulated quiescent cells. Dominant-negative Ras expression inhibits p70(s6k) stimulation by epidermal growth factor, demonstrating a requirement for Ras activity during p70(s6k) activation. FTI does not inhibit protein kinase B phosphorylation on Ser473, indicating that FTI does not act by inhibiting phosphatidylinositol 3-kinase. FTI also inhibits DNA synthesis in keratinocytes, and inhibition of DNA synthesis correlates closely with p70(s6k) inhibition. Rapamycin, an inhibitor of p70(s6k) and PHAS-1 phosphorylation, causes a 30-45% reduction in DNA synthesis in keratinocytes, while FTI induces an 80-90% reduction in DNA synthesis. These observations suggest that alteration of p70(s6k) and PHAS-1 function by FTI are responsible for a substantial portion of the growth-inhibitory properties of FTI. Together, these data demonstrate that p70(s6k) and PHAS-1 are novel downstream targets of FTI and suggest that the anti-tumor properties of FTI are probably due to the inhibition of multiple mitogenic pathways.
authors.affiliation: Vanderbilt Cancer Center, Vanderbilt University, Nashville, Tennessee 37232, USA.
authors.forename: B K
authors.initials: BK
authors.lastname: Law
authors.forename: P
authors.initials: P
authors.lastname: Nørgaard
authors.forename: L
authors.initials: L
authors.lastname: Gnudi
authors.forename: B B
authors.initials: BB
authors.lastname: Kahn
authors.forename: H S
authors.initials: HS
authors.lastname: Poulson
authors.forename: H L
authors.initials: HL
authors.lastname: Moses
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D019883:Alkyl and Aryl Transferases / Q000037:antagonists & inhibitors*; D000818:Animals; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D004261:DNA Replication / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D039642:Eukaryotic Initiation Factors; D051231:Farnesyltranstransferase; D015603:Keratinocytes / Q000187:drug effects / Q000201:enzymology; D008715:Methionine / Q000031:analogs & derivatives* / Q000494:pharmacology; D051379:Mice; D008807:Mice, Inbred BALB C; D008822:Mice, Transgenic; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D019893:Ribosomal Protein S6 Kinases / Q000037:antagonists & inhibitors*; D020123:Sirolimus / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D018631:ras Proteins / Q000378:metabolism