FRAP-p70s6K signaling is required for pancreatic cancer cell proliferation.
BACKGROUND
FRAP-p70s6K signaling regulates mitogenic responses to growth factors in eukaryotic cells. Constitutive p70s6K activation occurs in some human malignancies and may contribute to dysregulated cell growth. We examined whether inhibition of this pathway affects mitogen-induced proliferation and cell cycle progression of human pancreatic cancer cells in vitro.


METHODS
Quiescent BxPC3 and Panc-1 human pancreatic cancer cells treated with or without 20 ng/mL rapamycin (FRAP inhibitor) were repleted with 10% FCS to induce cell cycle entry. Proliferation was measured with MTT assay. Cell cycle and apoptosis were determined by FACS analysis. Phosphorylation of p70s6K, Akt, and cdc2 was evaluated by Western blot. Statistical analysis was by two-tailed t test (P < 0.05).


RESULTS
Rapamycin (Rapa) inhibited the phosphorylation of p70s6K while inducing G(1) cell cycle arrest (P < 0.005). In both cell lines, Rapa inhibited serum-induced proliferation (P < 0.05) without affecting apoptosis. Cdc2 phosphorylation was inhibited by 15 min with Rapa (not shown), consistent with cell cycle arrest. Akt phosphorylation was not affected, indicating FRAP specificity of Rapa.


CONCLUSIONS
FRAP-p70s6K signaling appears to be necessary for G(1)-to-S phase progression and proliferation in pancreatic cancer cells. This supports earlier work demonstrating a similar regulatory role for PI-3' kinase, an upstream activator of FRAP-p70s6K.
Shah
S A
SA
Department of Surgery, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
Potter
M W
MW
Ricciardi
R
R
Perugini
R A
RA
Callery
M P
MP
D000230:Adenocarcinoma; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002352:Carrier Proteins; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D005326:Fetal Proteins / Q000494:pharmacology; D005434:Flow Cytometry; D016193:G1 Phase / Q000187:drug effects / Q000502:physiology; D006801:Humans; D020104:Immunophilins / Q000378:metabolism*; D008934:Mitogens / Q000494:pharmacology; D010190:Pancreatic Neoplasms; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor); D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism*; D016196:S Phase / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000201:enzymology
D000903:Antibiotics, Antineoplastic; D016203:CDC2 Protein Kinase; D002352:Carrier Proteins; D005326:Fetal Proteins; D020104:Immunophilins; D008934:Mitogens; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; C546842:MTOR protein, human; C494918:AKT1 protein, human