Nuclear retinoic acid (RA) receptors (RARs) activate gene expression through dynamic interactions with coregulators in coordination with the ligand and phosphorylation processes. Here we show that during RA‐dependent activation of the RARα isotype, the p160 coactivator pCIP/ACTR/AIB‐1/RAC‐3/TRAM‐1/SRC‐3 is phosphorylated by p38MAPK. SRC‐3 phosphorylation has been correlated to an initial facilitation of RARα‐target genes activation, via the control of the dynamics of the interactions of the coactivator with RARα. Then, phosphorylation inhibits transcription via promoting the degradation of SRC‐3. In line with this, inhibition of p38MAPK markedly enhances RARα‐mediated transcription and RA‐dependent induction of cell differentiation. SRC‐3 phosphorylation and degradation occur only within the context of RARα complexes, suggesting that the RAR isotype defines a phosphorylation code through dictating the accessibility of the coactivator to p38MAPK. We propose a model in which RARα transcriptional activity is regulated by SRC‐3 through coordinated events that are fine‐tuned by RA and p38MAPK.

The peptidyl-prolyl-isomerase Pin1 interacts with phosphorylated proteins, altering their conformation. The retinoic acid receptor RARα and the acute-promyelocytic-leukemia–specific counterpart PML-RARα directly interact with Pin1. Overexpression of Pin1 inhibits ligand-dependent activation of RARα and PML-RARα. Inhibition is relieved by Pin1-targeted short interfering RNAs and by pharmacologic inhibition of the catalytic activity of the protein. Mutants of Pin1 catalytically inactive or defective for client-protein–binding activity are incapable of inhibiting ligand-dependent RARα transcriptional activity. Functional inhibition of RARα and PML-RARα by Pin1 correlates with degradation of the nuclear receptors via the proteasome-dependent pathway. In the acute myelogenous leukemia cell lines HL-60 and NB4, Pin1 interacts with RARα in a constitutive fashion. Suppression of Pin1 by a specific short hairpin RNA in HL-60 or NB4 cells stabilizes RARα and PML-RARα, resulting in increased sensitivity to the cytodifferentiating and antiproliferative activities of all-trans retinoic acid. Treatment of the two cell lines and freshly isolated acute myelogenous leukemia blasts (M1 to M4) with ATRA and a pharmacologic inhibitor of Pin1 causes similar effects. Our results add a further layer of complexity to the regulation of nuclear retinoic acid receptors and suggest that Pin1 represents an important target for strategies aimed at increasing the therapeutic index of retinoids. [Cancer Res 2009;69(3):1016–26

Patients with type 2 diabetes (T2DM) are at increased risk of fractures. The aim of this study is to analyze the prevalence and risk factors of osteoporosis and osteoporosis related fractures in postmenopausal women with T2DM. A total of 112 postmenopausal women with T2DM and 171 control nondiabetic women received a standardized questionnaire on osteoporosis risk factors, and were evaluated for bone mineral density (BMD, by using a dual energy X-ray absorptiometry), biochemical markers of bone and glucose metabolism, soluble receptor for advanced glycation end products (sRAGE) and its gene polymorphisms (rs1800625 or rs2070600). In T2DM patients the prevalence of osteoporosis was 25% and low trauma vertebral (Vfx) and non-vertebral fractures were found in 8% and 19% women, respectively. When compared between subjects with and without fractures, there were no significant differences in BMD at any site between the groups, except for distal radius, which was significantly lower in T2DM women with Vfx (p 2 h daily). Diabetes-specific parameters as well as RAGE polymorphisms did not associate with BMD or fractures in T2DM postmenopausal women. Lower levels of osteocalcin, namely in those with Vfx and higher sclerostin levels in those with low daily walking activity suggest lower bone remodeling and/or decreased bone quality in T2DM.