Reduced Proteolysis of Rabbit Growth Hormone (GH) Receptor Substituted with Mouse GH Receptor Cleavage Site

GH binding protein (GHBP) is a circulating form of the GH receptor (GHR) extracellular domain, which derives by alternative splicing of the GHR gene (in mice and rats) and by metalloprotease-mediated GHR proteolysis with shedding of the extracellular domain as GHBP (in rabbits, humans, and other species). Inducible proteolysis of either mouse (m) or rabbit (rb) GHR is detected in cell culture in response to phorbol ester and other stimuli, yielding a cell-associated GHR remnant (comprised of the cytoplasmic and transmembrane domains and a small portion of the proximal extracellular domain) and down-regulating GH signaling. In this report, we map the mGHR cleavage site by adenoviral overexpression of a membrane-anchored mGHR mutant lacking its cytoplasmic domain and purification and N-terminal sequencing of the phorbol 12-myristate 13-acetate-induced remnant protein. The sequence obtained was LEACEEDI, which matches the mGHR extracellular domain stem region sequence L265EACEEDI272, indicating that mGHR cle...