Abnormal growth of smooth muscle-like cells in lymphangioleiomyomatosis: Role for tumor suppressor TSC2

Am J Respir Cell Mol Biol. 2006 May;34(5):561-72. doi: 10.1165/rcmb.2005-0300OC. Epub 2006 Jan 19.


The TSC1 and TSC2 proteins, which function as a TSC1/TSC2 tumor suppressor complex, are associated with lymphangioleiomyomatosis (LAM), a genetic disorder characterized by the abnormal growth of smooth muscle-like cells in the lungs. The precise molecular mechanisms that modulate LAM cell growth remain unknown. We demonstrate that TSC2 regulates LAM cell growth. Cells dissociated from LAM nodules from the lungs of five different patients with LAM have constitutively activated S6K1, hyperphosphorylated ribosomal protein S6, activated Erk, and increased DNA synthesis compared with normal cells from the same patients. These effects were augmented by PDGF stimulation. Akt activity was unchanged in LAM cells. Rapamycin, a specific S6K1 inhibitor, abolished increased LAM cell growth. The full-length TSC2 was necessary for inhibition of S6 hyperphosphorylation and DNA synthesis in LAM cells, as demonstrated by co-microinjection of the C-terminus, which contains the GTPase activating protein homology domain, and the N-terminus, which binds TSC1. Our data demonstrate that increased LAM cell growth is associated with constitutive S6K1 activation, which is extinguishable by TSC2 expression. Loss of TSC2 GAP activity or disruption of the TSC1/TSC2 complex dysregulates S6K1 activation, which leads to abnormal cell proliferation associated with LAM disease.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Actins / metabolism
  • Cell Proliferation
  • Cells, Cultured
  • DNA / biosynthesis
  • Extracellular Signal-Regulated MAP Kinases / metabolism
  • Humans
  • Lymphangioleiomyomatosis / metabolism
  • Lymphangioleiomyomatosis / pathology*
  • Muscle, Smooth / growth & development*
  • Muscle, Smooth / pathology*
  • Phosphorylation / drug effects
  • Protein Kinases / metabolism
  • Protein Transport
  • Proto-Oncogene Proteins c-akt / metabolism
  • Recombinant Fusion Proteins / metabolism
  • Repressor Proteins / chemistry
  • Repressor Proteins / metabolism*
  • Ribosomal Protein S6 / metabolism
  • Sirolimus / pharmacology
  • TOR Serine-Threonine Kinases
  • Tuberous Sclerosis Complex 2 Protein
  • Tumor Suppressor Proteins / chemistry
  • Tumor Suppressor Proteins / metabolism*


  • Actins
  • Recombinant Fusion Proteins
  • Repressor Proteins
  • Ribosomal Protein S6
  • TSC2 protein, human
  • Tuberous Sclerosis Complex 2 Protein
  • Tumor Suppressor Proteins
  • DNA
  • Protein Kinases
  • MTOR protein, human
  • Proto-Oncogene Proteins c-akt
  • TOR Serine-Threonine Kinases
  • Extracellular Signal-Regulated MAP Kinases
  • Sirolimus