Ubiquitination-deubiquitination balance dictates ligand-stimulated PTHR sorting

Abstract

Parathyroid hormone receptors (PTHR) are promptly internalized upon stimulation by activating (PTH[1‐84], PTH[1‐34]) and non‐activating (PTH[7‐84], PTH[7‐34]) ligands. Here, we characterized the mechanism regulating the sorting of internalized receptors between recycling and degradative pathways. PTHR recycles faster after challenge with PTH(1‐34) than with PTH(7‐34). PTHR recycling is complete by 2 h after PTH(1‐34) stimulation, but incomplete at this time in cells treated with PTH(7‐34). The slower and incomplete recycling induced by PTH(7‐34) is due to proteasomal degradation. Both PTH(1‐34) and PTH(7‐34) induced PTHR polyubiquitination. Ubiquitination by PTH(1‐34) was transient, whereas receptor ubiquitination after PTH(7‐34) was sustained. PTH(1‐34), but not PTH(7‐34), induced expression of the PTHR‐specific deubiquitinating enzyme USP2. Overexpression of USP2 prevented PTH(7‐34)‐induced PTHR degradation. We conclude that PTH(1‐34) promotes coupled PTHR ubiquitination and deubiquitination, whereas PTH(7‐34) activates only ubiquitination, thereby leading to PTHR downregulation. These findings may explain PTH resistance in diseases associated with elevated PTH(7‐84) levels. © 2011 American Society for Bone and Mineral Research