Farnesyltransferase inhibitors reverse altered growth and distribution of actin filaments in Tsc-deficient cells via inhibition of both rapamycin-sensitive and -insensitive pathways.
Farnesyltransferase inhibitors (FTI) have been developed as anticancer drugs and are currently being evaluated in clinical trials. In this study, we have examined the effects of FTIs on Tsc-null cells to gain insight into their effects on farnesylated Rheb GTPase. This protein is involved in the activation of mTOR/S6K signaling and is down-regulated by the Tsc1/Tsc2 complex. Both Tsc1(-/-) and Tsc2(-/-) mouse embryonic fibroblasts exhibit constitutive activation of S6K and grow in the absence of serum. Two different FTI compounds, the clinical compound BMS-214662 and the newly described BMS-225975, inhibit the constitutive activation of mTOR/S6K signaling and block serum-free growth of the Tsc-null mouse embryonic fibroblasts. We have also found that Tsc-null mouse embryonic fibroblasts grow under anchorage-independent conditions and that both FTI compounds inhibit this soft agar growth. These FTI effects are similar to those observed with rapamycin. Another interesting phenotype of Tsc-null mouse embryonic fibroblasts is that they are round and contain actin filaments predominantly at the cell periphery. The addition of FTIs, but not rapamycin, led to the reappearance of intracellular actin filaments and reduction of peripheral actin filaments. The ability of FTI to rearrange actin filaments seems to be largely mediated by the inhibition of Rheb protein, as induction of intracellular actin filaments by FTI was much less efficient in Tsc2-null cells expressing Rheb (M184L), a geranylgeranylated mutant Rheb that can bypass farnesylation. These results reveal that FTIs inhibit Rheb, causing two different effects in Tsc-deficient cells, one on growth and the other on actin filament distribution.
Gau
Chia-Ling
CL
Department of Microbiology, Immunology, and Molecular Genetics, Jonsson Comprehensive Cancer Center, Molecular Biology Institute, University of California at Los Angeles, 90095, USA.
Kato-Stankiewicz
Juran
J
Jiang
Chen
C
Miyamoto
Susie
S
Guo
Lea
L
Tamanoi
Fuyuhiko
F
D000199:Actins / Q000378:metabolism*; D019883:Alkyl and Aryl Transferases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D002522:Chlorocebus aethiops; D003599:Cytoskeleton / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D051231:Farnesyltranstransferase; D005347:Fibroblasts; D006801:Humans; D051379:Mice; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D000076205:Ras Homolog Enriched in Brain Protein; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D020123:Sirolimus / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism
D000199:Actins; D004791:Enzyme Inhibitors; D009479:Neuropeptides; D000076205:Ras Homolog Enriched in Brain Protein; D012097:Repressor Proteins; C490213:Rheb protein, mouse; C000624650:TSC1 protein, human; C000624653:TSC2 protein, human; C000624651:Tsc1 protein, mouse; C000624654:Tsc2 protein, mouse; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D019883:Alkyl and Aryl Transferases; D051231:Farnesyltranstransferase; D011494:Protein Kinases; C546842:MTOR protein, human; C546843:mTOR protein, mouse; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; D020559:Monomeric GTP-Binding Proteins; D020123:Sirolimus