title: EGF stimulates mesangial cell mitogenesis via PI3-kinase-mediated MAPK-dependent and AKT kinase-independent manner: involvement of c-fos and p27Kip1.
abstract: Epidermal growth factor (EGF) is a potent mitogen for mesangial cells. The mechanism by which EGF induces DNA synthesis is not precisely understood. We investigated the role of phosphatidylinositol (PI)3-kinase in regulating mitogenesis. EGF increased PI3-kinase activity resulting in stimulation of PDK-1 and Akt kinase activities. Blocking of PI3-kinase activity using LY-294002 or adenoviral expression of PTEN, which dephosphorylates PI3,4,5-tris-phosphate and thus inactivates PI3-kinase signaling, significantly inhibits EGF-induced DNA synthesis. Expression of dominant-negative Akt kinase, however, had no effect on DNA synthesis. But it inhibited EGF-induced phosphorylation of FoxO3a transcription factor, thus demonstrating its functional consequences. These data indicate that EGF increases the DNA synthesis in a PI3-kinase-dependent but Akt-independent manner. In addition to activating PI3-kinase signaling, EGF increased Erk1/2 MAPK activity, leading to transcriptional activation of its nuclear target Elk-1 and resulting in c-fos expression. Inhibition of MAPK activity by MEK inhibitor U-0126 abolished EGF-induced DNA synthesis. Because EGF activates PI3-kinase, which also regulates DNA synthesis, the effect of PI3-kinase on MAPK activity was also examined. Inhibition of PI3-kinase signaling blocked EGF-induced MAPK activity as well as Elk-1-dependent reporter transcription and c-fos gene transcription. To further determine the mechanism of EGF-induced DNA synthesis, we investigated the effect of EGF on the cyclin-dependent kinase inhibitor p27(Kip1). EGF reduced the expression of p27(Kip1). Inhibition of PI3-kinase action or MAPK activity abolished the reduction in p27(Kip1) expression induced by EGF. These data provide the evidence that a linear signal transduction pathway involving PI3-kinase-dependent MAPK regulates EGF-induced DNA synthesis in mesangial cells by regulating c-fos and p27(Kip1) expression.
authors.affiliation: Dept. of Medicine, University of Texas Health Science Center at San Antonio, TX 78229-3900, USA.
authors.forename: Lenin
authors.initials: L
authors.lastname: Mahimainathan
authors.forename: Nandini
authors.initials: N
authors.lastname: Ghosh-Choudhury
authors.forename: Balachandar A
authors.initials: BA
authors.lastname: Venkatesan
authors.forename: Ratna S
authors.initials: RS
authors.lastname: Danda
authors.forename: Goutam Ghosh
authors.initials: GG
authors.lastname: Choudhury
mesh_terms: D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004791:Enzyme Inhibitors / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000502:physiology*; D005786:Gene Expression Regulation; D005920:Glomerular Mesangium / Q000166:cytology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008938:Mitosis / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction; D025521:Tumor Suppressor Proteins / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004791:Enzyme Inhibitors; D004815:Epidermal Growth Factor; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D016760:Proto-Oncogene Proteins c-fos; D025521:Tumor Suppressor Proteins; C493962:Cdkn1b protein, rat; C494920:Akt1 protein, rat