Role of the Phosphatidylinositol 3-kinase/Akt and mTOR/P70S6-kinase Pathways in the Proliferation and Apoptosis in Multiple Myeloma

Oncogene. 2002 Sep 26;21(43):6587-97. doi: 10.1038/sj.onc.1205923.

Abstract

Multiple myeloma (MM) is a plasma cell malignancy preliminary localized in the bone marrow and characterized by its capacity to disseminate. IL-6 and IGF-1 have been shown to mediate proliferative and anti-apoptotic signals in plasmocytes. However, in primary plasma-cell leukemia (PCL) and in end-stage aggressive extramedullar disease, the cytokine requirement for both effects may be not mandatory. This suggests that constitutive activation of signaling pathways occurs. One of the signaling pathways whose deregulation may play an oncogenic role in MM is the phosphatidylinositol 3-kinase (PI 3-K) pathway. In human growth factor-independent MM cell lines OPM2 and RPMI8226, we show that the PI 3-K inhibitors LY294002 and Wortmannin strongly inhibited cell proliferation, whereas inhibition of the mammalian Target Of Rapamycin (mTOR)/P70-S6-kinase (P70(S6K)) pathway with rapamycin or of the Mitogen-Activated Protein Kinase (MAPK) pathway with PD98059 had minimal effect on proliferation. In both cell lines, constitutive activation of the PI 3-K/Akt/FKHRL-1, mTOR/P70(S6K) and MAPK pathways was detected. LY294002 inhibited phosphorylation of Akt, FKHRL-1 and P70(S6K) but had no effect on ERK1/2 phosphorylation, indicating that the PI 3-K and MAPK pathways are independent. IGF-1 but not IL-6 increased phosphorylation of Akt, FKHRL-1 and P70(S6K). Purified plasmocytes from four patients with MM and two patients with primary PCL were studied. In three of them including the two patients with PCL, constitutive phosphorylation of Akt, FKHRL-1 and P70(S6K) was present, inhibited by LY294002 and enhanced by IGF-1. In these patients with constitutive Akt activation, normal PTEN expression was detected. PI 3-K inhibition induced caspase-dependent apoptosis as confirmed by inhibition with the large spectrum caspase inhibitor Z-VAD-FMK and cleavage of pro-caspase-3. Both cell lines spontaneously expressed Skp2 and cyclin D1 proteins at high levels but no p27(Kip1) protein. In the presence of LY294002, cell-cycle arrest in G0/G1 was observed, p27(Kip1) protein expression was up-regulated whereas the expression of both Skp2 and cyclin D1 dramatically diminished. PI 3-K-dependent GSK-3alpha/beta constitutive phosphorylation was also detected in OPM2 cells that may contribute to high cyclin D1 expression. Overall, our results suggest that PI 3-K has a major role in the control of proliferation and apoptosis of growth factor-independent MM cell lines. Most of the biological effects of PI 3-K activation in these cell lines may be mediated by the opposite modulation of p27(Kip1) and Skp2 protein expression. Moreover, constitutive activation of this pathway is a frequent event in the biology of MM in vivo and may be more frequently observed in PCL.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis*
  • Caspases / physiology
  • Cell Cycle
  • Cell Cycle Proteins / analysis
  • Cell Division
  • Cell Line
  • Cyclin D1 / analysis
  • Fas Ligand Protein
  • Humans
  • Interleukin-6 / biosynthesis
  • Membrane Glycoproteins / physiology
  • Microfilament Proteins / biosynthesis
  • Mitogen-Activated Protein Kinases / physiology
  • Multiple Myeloma / pathology*
  • Muscle Proteins*
  • PTEN Phosphohydrolase
  • Phosphatidylinositol 3-Kinases / physiology*
  • Phosphoric Monoester Hydrolases / analysis
  • Protein Kinases / physiology*
  • Protein-Serine-Threonine Kinases*
  • Proto-Oncogene Proteins / physiology*
  • Proto-Oncogene Proteins c-akt
  • Ribosomal Protein S6 Kinases / physiology*
  • S-Phase Kinase-Associated Proteins
  • TOR Serine-Threonine Kinases
  • Tumor Suppressor Proteins / analysis
  • fas Receptor / physiology

Substances

  • Cell Cycle Proteins
  • FASLG protein, human
  • Fas Ligand Protein
  • Fasl protein, mouse
  • Interleukin-6
  • Membrane Glycoproteins
  • Microfilament Proteins
  • Muscle Proteins
  • Proto-Oncogene Proteins
  • S-Phase Kinase-Associated Proteins
  • Tagln protein, mouse
  • Tumor Suppressor Proteins
  • fas Receptor
  • Cyclin D1
  • Protein Kinases
  • Phosphatidylinositol 3-Kinases
  • MTOR protein, human
  • TOR Serine-Threonine Kinases
  • mTOR protein, mouse
  • AKT1 protein, human
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Ribosomal Protein S6 Kinases
  • Mitogen-Activated Protein Kinases
  • Phosphoric Monoester Hydrolases
  • PTEN Phosphohydrolase
  • PTEN protein, human
  • Caspases