Beta-adrenergic receptor kinase-like activity and beta-arrestin are expressed in osteoblastic cells.
Biologic responses to peptide calciotropic hormones, such as parathyroid hormone (PTH) and calcitonin, exhibit desensitization. As with most hormones, however, the mechanisms of desensitization are not completely understood. For the beta 2-adrenergic receptor (beta 2AR) system, which is coupled to adenylyl cyclase via the stimulatory guanine nucleotide-binding regulatory (G5) protein, homologous desensitization is mediated in part by a receptor-specific kinase (beta ARK) and a soluble cofactor (beta-arrestin). Recently, this system has been reported to be involved in rapid homologous desensitization of the PTH/parathyroid hormone receptor protein (PTHrP) receptor. We have identified the presence of this system in bone using reverse-transcriptase PCR. Nucleotide sequence of PCR fragments from ROS 17/2.8 cells revealed 100% identity with rat brain beta ARK1 and beta-arrestin 1 sequences. Northern analyses with RNA from ROS 17/2.8, UMR 106-H5 cells, and primary cultures of nontransformed neonatal rat calvariae demonstrated two mRNA species of 4 and 2.6 kilobases (kb) for beta ARK and 7.5 kb for beta-arrestin, comparable to those found in bovine brain. beta ARK-like activity was demonstrated in cytosolic extracts of the UMR 106-H5 cells by assessing phosphorylation of the retinal photoreceptor, rhodopsin, by the extracts. Phosphorylation was enhanced with light-activated rhodopsin and by bovine brain G beta gamma subunits; heparin inhibited phosphorylation. These findings are characteristic of beta ARK. Expression of beta-arrestin in the UMR 106-H5 cells was confirmed by immunoblot. Thus, osteoblastic cells express proteins, beta ARK, and beta-arrestin, which may regulate desensitization of calciotropic hormone receptors.
Bliziotes
M
M
Bone and Mineral Research Unit, Portland VAMC, Oregon, USA.
Murtagh
J
J
Wiren
K
K
D000818:Animals; D019390:Arrestins / Q000096:biosynthesis* / Q000235:genetics; D001483:Base Sequence; D015152:Blotting, Northern; D015139:Blotting, Southern; D015153:Blotting, Western; D017868:Cyclic AMP-Dependent Protein Kinases / Q000096:biosynthesis* / Q000378:metabolism; D010006:Osteoblasts / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D051381:Rats; D014407:Tumor Cells, Cultured; D051552:beta-Adrenergic Receptor Kinases; D000071559:beta-Arrestin 1; D000071557:beta-Arrestins
C000605256:Arrb1 protein, rat; D019390:Arrestins; D000071559:beta-Arrestin 1; D000071557:beta-Arrestins; D017868:Cyclic AMP-Dependent Protein Kinases; D051552:beta-Adrenergic Receptor Kinases