Osteoblast regulation via ligand-activated nuclear trafficking of the oxytocin receptor
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Authors: Di Benedetto, Adriana; Sun, Li; Zambonin, Carlo G.; Tamma, Roberto; Nico, Beatrice; Calvano, Cosima D.; Colaianni, Graziana; Ji, Yaoting; Mori, Giorgio; Grano, Maria; Lu, Ping; Colucci, Silvia; Yuen, Tony; New, Maria I.; Zallone, Alberta; Zaidi, Mone
Abstract
We report that oxytocin (Oxt) receptors (Oxtrs), on stimulation by the ligand Oxt, translocate into the nucleus of osteoblasts, implicating this process in the action of Oxt on osteoblast maturation. Sequential immunocytochemistry of intact cells or isolated nucleoplasts stripped of the outer nuclear membrane showed progressive nuclear localization of the Oxtr; this nuclear translocation was confirmed by monitoring the movement of Oxtr-EGFP as well as by immunogold labeling. Nuclear Oxtr localization was conclusively shown by Western immunoblotting and MS of nuclear lysate proteins. We found that the passage of Oxtrs into the nucleus was facilitated by successive interactions with beta-arrestins (Arrbs), the small GTPase Rab5, importin-beta (Kpnb1), and transportin-1 (Tnpo1). siRNA-mediated knockdown of Arrb1, Arrb2, or Tnpo1 abrogated Oxt-induced expression of the osteoblast differentiation genes osterix (Sp7), Atf4, bone sialoprotein (Ibsp), and osteocalcin (Bglap) without affecting Erk phosphorylation. Likewise and again, without affecting pErk, inhibiting Arrb recruitment by mutating Ser rich clusters of the nuclear localization signal to Ala abolished nuclear import and Oxtr-induced gene expression. These studies define a previously unidentified mechanism for Oxtr action on bone and open possibilities for direct transcriptional modulation by nuclear G protein-coupled receptors.
Nuclear ARRB1 induces pseudohypoxia and cellular metabolism reprogramming in prostate cancer
EMBO JOURNAL
Authors: Zecchini, Vincent; Madhu, Basetti; Russell, Roslin; Pertega-Gomes, Nelma; Warren, Anne; Gaude, Edoardo; Borlido, Joana; Stark, Rory; Ireland-Zecchini, Heather; Rao, Roheet; Scott, Helen; Boren, Joan; Massie, Charlie; Asim, Mohammad; Brindle, Kevin; Griffiths, John; Frezza, Christian; Neal, David E.; Mills, Ian G.
Abstract
Tumour cells sustain their high proliferation rate through metabolic reprogramming, whereby cellular metabolism shifts from oxidative phosphorylation to aerobic glycolysis, even under normal oxygen levels. Hypoxia-inducible factor 1A (HIF1A) is a major regulator of this process, but its activation under normoxic conditions, termed pseudohypoxia, is not well documented. Here, using an integrative approach combining the first genome-wide mapping of chromatin binding for an endocytic adaptor, ARRB1, both in vitro and in vivo with gene expression profiling, we demonstrate that nuclear ARRB1 contributes to this metabolic shift in prostate cancer cells via regulation of HIF1A transcriptional activity under normoxic conditions through regulation of succinate dehydrogenase A (SDHA) and fumarate hydratase (FH) expression. ARRB1-induced pseudohypoxia may facilitate adaptation of cancer cells to growth in the harsh conditions that are frequently encountered within solid tumours. Our study is the first example of an endocytic adaptor protein regulating metabolic pathways. It implicates ARRB1 as a potential tumour promoter in prostate cancer and highlights the importance of metabolic alterations in prostate cancer.