Peroxisome proliferator-activated receptor-gamma and retinoic acid X receptor alpha represses the TGFbeta1 gene via PTEN-mediated p70 ribosomal S6 kinase-1 inhibition: role for Zf9 dephosphorylation

• Published in: Molecular pharmacology 2006-07, Vol.70 (1), p.415-425
• Main Authors: Lee, Seung Jin, Yang, Eun Kyoung, Kim, Sang Geon
• Format: Article
• Language: English
• Subjects: Animals; Cell Line, Tumor; DNA-Binding Proteins - metabolism; Gene Expression - drug effects; Immunoblotting; Luciferases - genetics; Luciferases - metabolism; Mitogen-Activated Protein Kinase 1 - metabolism; Mitogen-Activated Protein Kinase 3 - metabolism; Phosphorylation - drug effects; PPAR gamma - agonists; PPAR gamma - physiology; Promoter Regions, Genetic - genetics; Prostaglandin D2 - analogs & derivatives; Prostaglandin D2 - pharmacology; Protein Kinases - metabolism; Proto-Oncogene Proteins c-akt - metabolism; PTEN Phosphohydrolase - metabolism; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Retinoid X Receptors - agonists; Retinoid X Receptors - physiology; Reverse Transcriptase Polymerase Chain Reaction; Ribosomal Protein S6 Kinases, 70-kDa - antagonists & inhibitors; Ribosomal Protein S6 Kinases, 70-kDa - metabolism; TOR Serine-Threonine Kinases; Transfection; Transforming Growth Factor alpha - genetics; Tretinoin - pharmacology
• ISSN: 0026-895X

Peroxisome proliferator-activated receptor (PPAR)-gamma and retinoic acid X receptor (RXR) heterodimer regulates cell growth and differentiation. Zinc finger transcription factor-9 (Zf9), whose phosphorylation promotes target genes, is a transcription factor essential for transactivation of the transforming growth factor (TGF)-beta1 gene. This study investigated whether activation of PPARgamma-RXR heterodimer inhibits TGFbeta1 gene transcription and Zf9 phosphorylation and, if so, what signaling pathway regulates it. Either 15-deoxy-delta(12,14)-prostaglandin J2 (PGJ2) or 9-cis-retinoic acid (RA) treatment decreased the TGFbeta1 mRNA level in L929 fibroblasts. PGJ2 + RA, compared with individual treatment alone, synergistically inhibited the TGFbeta1 gene expression, which was abrogated by PPARgamma antagonists. Likewise, PGJ2 + RA decreased luciferase expression from the TGFbeta1 gene promoter. Promoter deletion analysis of the TGFbeta1 gene revealed that pGL3-323 making up to -323-base pair region, but lacking PPAR-responsive elements, responded to PGJ2 + RA. PGJ2 + RA treatment inhibited the activity of p70 ribosomal S6 kinase-1 (S6K1), abolishing Zf9 phosphorylation at serine as did rapamycin [a mammalian target of rapamycin (mTOR) inhibitor]. Zf9 dephosphorylation by PGJ2 + RA was reversed by transfection of cells with the plasmid encoding constitutively active S6K1 (CA-S6K1). Transfection with dominant negative S6K1 inhibited the TGFbeta1 gene. TGFbeta1 gene repression by PGJ2 + RA was consistently antagonized by CA-S6K1. Ectopic expression of PPARgamma1 and RXRalpha repressed pGL3-323 transactivation with S6K1 inhibition, which was abrogated by CA-S6K1 transfection. PGJ2 + RA induced phosphatase and tensin homolog deleted on chromosome 10 (PTEN), whose overexpression repressed the TGFbeta1 gene through S6K1 inhibition, decreasing extracellular signal-regulated kinase 1/2-90-kDa ribosomal S6 kinase 1 and Akt-mTOR phosphorylations. Data indicate that activation of PPARgamma-RXR heterodimer represses the TGFbeta1 gene and induces Zf9 dephosphorylation via PTEN-mediated S6K1 inhibition, providing insight into pharmacological manipulation of the TGFbeta1 gene regulation.