FRAP-p70s6K signaling is required for pancreatic cancer cell proliferation

J Surg Res. 2001 May 15;97(2):123-30. doi: 10.1006/jsre.2001.6145.


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.

MeSH terms

  • Adenocarcinoma*
  • Antibiotics, Antineoplastic / pharmacology
  • CDC2 Protein Kinase / metabolism
  • Carrier Proteins*
  • Cell Division / drug effects
  • Cell Division / physiology
  • Fetal Proteins / pharmacology
  • Flow Cytometry
  • G1 Phase / drug effects
  • G1 Phase / physiology
  • Humans
  • Immunophilins / metabolism*
  • Mitogens / pharmacology
  • Pancreatic Neoplasms*
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphorylation
  • Phosphotransferases (Alcohol Group Acceptor)*
  • Protein Kinases / metabolism
  • Protein Serine-Threonine Kinases*
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-akt
  • Ribosomal Protein S6 Kinases / metabolism*
  • S Phase / drug effects
  • S Phase / physiology
  • Signal Transduction / drug effects
  • Signal Transduction / physiology*
  • Sirolimus / pharmacology
  • TOR Serine-Threonine Kinases
  • Tumor Cells, Cultured / cytology
  • Tumor Cells, Cultured / enzymology


  • Antibiotics, Antineoplastic
  • Carrier Proteins
  • Fetal Proteins
  • Mitogens
  • Proto-Oncogene Proteins
  • Protein Kinases
  • Phosphotransferases (Alcohol Group Acceptor)
  • MTOR protein, human
  • AKT1 protein, human
  • Protein Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Ribosomal Protein S6 Kinases
  • TOR Serine-Threonine Kinases
  • CDC2 Protein Kinase
  • Immunophilins
  • Sirolimus