title: Ligand modulates VDR-Ser/Thr protein phosphatase interaction and p70S6 kinase phosphorylation in a cell-context-dependent manner.
abstract: We have recently shown that in colon cancer cells, Vitamin D receptor (VDR) interacts with the catalytic subunit of Ser/Thr protein phosphatases, PP1c and PP2Ac, and induces their enzymatic activity in a ligand-dependent manner. The VDR-PP1c and VDR-PP2Ac interactions were ligand independent in vivo, and 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3))-mediated increase in VDR-associated phosphatase activity resulted in dephosphorylation and inactivation of p70S6 kinase in colon cancer cells. Here, we demonstrate that in myeloid leukemia cells, 1,25(OH)(2)D(3) treatment increased the Thr389 phosphorylation of p70S6 kinase. Accordingly, 1,25(OH)(2)D(3) decreased VDR-associated Ser/Thr protein phosphatase activity by dissociating VDR-PP1c and VDR-PP2Ac interactions. Further, 1,25(OH)(2)D(3) increased the association between VDR and Thr389 phosphorylated p70S6 kinase. Finally, by using non-secosteroidal VDR ligands, we demonstrate a separation between transactivation and p70S6 kinase phosphorylation activities of VDR and show pharmacologically that p70S6 kinase phosphorylation correlates with HL-60 cell differentiation.
authors.affiliation: Inflammation, Immunomodulation, Gene Regulation and Bone Research, Indianapolis, IN-46285, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Bettoun
authors.forename: Jianfen
authors.initials: J
authors.lastname: Lu
authors.forename: Berket
authors.initials: B
authors.lastname: Khalifa
authors.forename: Ying
authors.initials: Y
authors.lastname: Yee
authors.forename: William W
authors.initials: WW
authors.lastname: Chin
authors.forename: Sunil
authors.initials: S
authors.lastname: Nagpal
mesh_terms: D045744:Cell Line, Tumor; D002469:Cell Separation; D005434:Flow Cytometry; D006801:Humans; D008024:Ligands; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D054645:Protein Phosphatase 1; D018167:Receptors, Calcitriol / Q000378:metabolism*; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism*
chemical_list: D008024:Ligands; D018167:Receptors, Calcitriol; D019893:Ribosomal Protein S6 Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1