title: Phosphorylation of the retinoic acid receptor-alpha by protein kinase A.
abstract: The phosphorylation of retinoic acid receptor-alpha 1 (RAR alpha 1) by PKA was investigated both in vitro and in vivo. We show that bacterially expressed RAR alpha 1 is phosphorylated in vitro by protein kinase A (PKA) at the unique serine residue 369 located in the C-terminal end of the E region. We also show that RAR alpha 1 overexpressed in COS-1 cells is phosphorylated on multiple serine residues and that phosphorylation at serine 369 occurs only when COS-1 cells are cotransfected with PKA or treated with forskolin. RAR alpha 1 mutants were constructed in which serine 369 was replaced by an alanine (S369A) or a glutamic acid (S369E) residue. Comparison of the tryptic phosphopeptide patterns of wild type and mutated RAR alpha 1 overexpressed in COS-1 cells allowed us to confirm that serine 369 is the unique phosphorylation site for PKA in cultured cells. The DNA-binding efficiency of RAR alpha/retinoid X receptor-alpha (RXR alpha) heterodimers was enhanced in vitro by the S369E mutation. However, in transfected RAC65 cells, the same S369E mutation did not affect the ligand-dependent transcriptional activation by RAR alpha 1 of reporter genes containing a retinoic acid (RA)-response element. In contrast, the S369A mutation slightly decreased both DNA binding and the efficiency of PKA to enhance RA-induced transactivation by RAR alpha 1. Finally, we show that endogenous RAR alpha is also phosphorylated in vivo at serine 369 in forskolin-treated F9 cells, supporting the idea that phosphorylation of RARs at this site is involved in the modulation of the RA-induced differentiation of F9 cells by (Bu)2cAMP.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D018014:Gene Transfer Techniques; D008969:Molecular Sequence Data; D010766:Phosphorylation; D017354:Point Mutation; D011493:Protein Kinase C / Q000378:metabolism*; D018168:Receptors, Retinoic Acid / Q000235:genetics / Q000378:metabolism*; D000072482:Retinoic Acid Receptor alpha; D015533:Transcriptional Activation
chemical_list: D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; D011493:Protein Kinase C