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Farnesyltransferase inhibitor induces rapid growth arrest and blocks p70s6k activation by multiple stimuli
B K Law1, P Norgaard, H L Moses
1Vanderbilt Ingram Cancer Center, Nashville, Tennessee 37232, USA.
Abstract:
We have previously shown that the peptidomimetic farnesyltransferase inhibitor L-744,832 (FTI) inhibits p70s6k activation and cell growth in a mouse keratinocyte cell line but only at concentrations of FTI significantly higher than those required for the inhibition of Ras farnesylation. Here we show that the rapid kinetics of FTI inhibition of DNA synthesis (within 1.5 h) in both normal and v-K-Ras transformed keratinocytes matches the rapid kinetics of p70s6k inhibition observed previously. It is further shown that FTI inhibits p70s6k activation in response to serum, phorbol myristate acetate, and increased amino acid levels. The phosphatase inhibitor calyculin A partially reverses the FTI-induced dephosphorylation of p70s6k, suggesting that FTI may act upstream of a protein phosphatase. A rapamycin-resistant mutant of p70s6k is shown to be resistant to FTI-induced dephosphorylation of the major rapamycin-sensitive phosphorylation site of p70s6k, Thr(389). Together, these data demonstrate that FTI rapidly inhibits DNA synthesis irrespective of the presence of v-K-Ras and that FTI inhibits p70s6k activation in response to multiple stimuli. Because the FTI L-744,832 mimics many of the effects of rapamycin, this FTI may prove effective against tumors that exhibit inappropriate activation of the mTOR/p70s6k pathway.
Insights
The farnesyltransferase inhibitor L-744,832 (FTI) rapidly inhibits DNA synthesis and p70s6k activation in keratinocytes. This FTI may be effective against tumors with mTOR/p70s6k pathway activation.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Farnesyltransferase inhibitor L-744,832 (FTI) previously shown to inhibit p70s6k activation and cell growth.
- FTI inhibition of p70s6k activation occurs at higher concentrations than Ras farnesylation inhibition.
Purpose of the Study:
- To investigate the kinetics and stimuli of FTI-induced p70s6k inhibition.
- To determine the mechanism by which FTI affects p70s6k phosphorylation.
- To assess the potential of FTI as a therapeutic agent for tumors with aberrant mTOR/p70s6k signaling.
Main Methods:
- Assessed DNA synthesis inhibition kinetics in normal and v-K-Ras transformed keratinocytes.
- Investigated FTI's effect on p70s6k activation in response to serum, PMA, and amino acid levels.
- Utilized phosphatase inhibitor calyculin A to probe FTI's mechanism of action.
- Examined FTI's effect on a rapamycin-resistant p70s6k mutant.
Main Results:
- FTI rapidly inhibits DNA synthesis (within 1.5 h) in both normal and v-K-Ras keratinocytes.
- FTI inhibits p70s6k activation induced by serum, PMA, and increased amino acid levels.
- FTI-induced p70s6k dephosphorylation is partially reversed by calyculin A, suggesting FTI acts upstream of a phosphatase.
- A rapamycin-resistant p70s6k mutant is resistant to FTI-induced dephosphorylation at Thr(389).
Conclusions:
- FTI rapidly inhibits DNA synthesis independently of v-K-Ras.
- FTI effectively inhibits p70s6k activation across various stimuli.
- FTI's mechanism involves upstream regulation of a protein phosphatase.
- FTI mimics rapamycin's effects and shows promise for treating mTOR/p70s6k pathway-driven tumors.