Parathyroid hormone receptor internalization is independent of protein kinase A and phospholipase C activation

Parathyroid hormone (PTH) and PTH-related peptide (PTHrP) binding to their common receptor stimulates second messenger accumulation, receptor phosphor ylation, and internalization. LLC-PK1 cells expressing a green fluorescent protein-tagged PTH/PTHrP receptor show time- and dose-dependent receptor in ternalization. The internalized receptors colocalize with clathrin-coated p its. Internalization is stimulated by PTH analogs that bind to and activate the PTH/PTHrP receptor. Cell lines expressing a mutant protein kinase A re gulatory subunit that is resistant to cAMP and/or a mutant receptor (DSEL m utant) that does not activate phospholipase C internalize their receptors n ormally. In addition, internalization of the wild-type receptor and the DSE L mutant is stimulated by the PTH analog [Gly(1),Arg(19)]hPTH-(1-28), which does not stimulate phospholipase C. Forskolin, IBMX, and the active phorbo l ester, phorbol-12-myristate-13-acetate, did not promote receptor internal ization or increase PTH-induced internalization. These data indicate that l igand-induced internalization of the PTH/PTHrP receptor requires both ligan d binding and receptor activation but does not involve stimulation of adeny late cyclase/protein kinase A or phospholipase C/protein kinase C.