mTOR regulates expression of slit diaphragm proteins and cytoskeleton structure in podocytes

Am J Physiol Renal Physiol. 2009 Feb;296(2):F418-26. doi: 10.1152/ajprenal.90319.2008. Epub 2008 Nov 19.

Abstract

The immunosuppressive mammalian target of rapamycin (mTOR) inhibitors can cause proteinuria, especially in kidney and heart transplanted patients. Podocytes play a major role in establishing the selective permeability of the blood-urine filtration barrier. Damage of these cells leads to proteinuria, a hallmark of most glomerular diseases. Interestingly, podocyte damage and focal segmental glomerulosclerosis can occur after treatment with an mTOR inhibitor in some transplant patients. To investigate the mechanisms of mTOR inhibitor-induced podocyte damage, we analyzed the effect of rapamycin on mTOR signaling and cellular function in human podocytes. We found that prolonged rapamycin treatment reduced the expression of total mTOR, which correlates with diminished levels of mTOR phosphorylation at Ser(2448) and Ser(2481). In addition, treatment with rapamycin reduced rictor expression and mTORC2 formation, resulting in a reduced phosphorylation of protein kinase B at Ser(473). The expression level of the slit-diaphragm proteins nephrin and transient receptor potential cation channel 6 as well as the cytoskeletal adaptor protein Nck significantly decreased. Moreover, rapamycin reduced cell adhesion and cell motility, which was accompanied by an enhanced formation of dot-like actin-rich structures. Our data provide new molecular insights explaining which pathways and molecules are affected in podocytes by an imbalanced mTOR function because of rapamycin treatment.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / metabolism
  • Adaptor Proteins, Signal Transducing
  • Carrier Proteins / metabolism
  • Cell Adhesion / drug effects
  • Cell Line
  • Cell Movement / drug effects
  • Cell Survival / drug effects
  • Cytoskeleton / drug effects
  • Humans
  • Immunoprecipitation
  • Immunosuppressive Agents / pharmacology*
  • Intercellular Junctions / drug effects*
  • Membrane Proteins / metabolism
  • Oncogene Proteins / metabolism
  • Phosphorylation
  • Podocytes / cytology
  • Podocytes / drug effects*
  • Podocytes / metabolism
  • Protein Kinases / metabolism*
  • Proteins / metabolism
  • Proto-Oncogene Proteins c-akt / metabolism
  • Rapamycin-Insensitive Companion of mTOR Protein
  • Regulatory-Associated Protein of mTOR
  • Signal Transduction / drug effects
  • Sirolimus / pharmacology*
  • TOR Serine-Threonine Kinases
  • TRPC Cation Channels / metabolism
  • TRPC6 Cation Channel

Substances

  • Actins
  • Adaptor Proteins, Signal Transducing
  • Carrier Proteins
  • Immunosuppressive Agents
  • Membrane Proteins
  • Nck protein
  • Oncogene Proteins
  • Proteins
  • RICTOR protein, human
  • RPTOR protein, human
  • Rapamycin-Insensitive Companion of mTOR Protein
  • Regulatory-Associated Protein of mTOR
  • TRPC Cation Channels
  • TRPC6 Cation Channel
  • TRPC6 protein, human
  • nephrin
  • Protein Kinases
  • MTOR protein, human
  • TOR Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Sirolimus