Article

Parathyroid Hormone Receptor Trafficking Contributes to the Activation of Extracellular Signal-regulated Kinases but Is Not Required for Regulation of cAMP Signaling

Division of Endocrinology and Metabolism, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Journal of Biological Chemistry (Impact Factor: 4.57). 04/2005; 280(12):11281-8. DOI: 10.1074/jbc.M413393200
Source: PubMed

ABSTRACT

Agonist-mediated activation of the type 1 parathyroid hormone receptor (PTH1R) results in several signaling events and receptor endocytosis. It is well documented that arrestins contribute to desensitization of both G(s)- and G(q)-mediated signaling and mediate PTH1R internalization. However, whether PTH1R trafficking directly contributes to signaling remains unclear. To address this question, we investigated the role of PTH1R trafficking in cAMP signaling and activation of extracellular signal-regulated kinases ERK1/2 in HEK-293 cells. Dominant negative forms of dynamin (K44A-dynamin) and beta-arrestin1 (beta-arrestin1-(319-418)) abrogated PTH1R internalization but had no effect on cAMP signaling; neither acute cAMP production by PTH nor desensitization and resensitization of cAMP signaling were affected. Therefore, PTH1R trafficking is not necessary for regulation of cAMP signaling. PTH-(1-34) induced rapid and robust activation of ERK1/2. A PTHrP-based analog ([p-benzoylphenylalanine1, Ile5,Arg(11,13),Tyr36]PTHrP-(1-36)NH2), which selectively activates the G(s)/cAMP pathway without inducing PTH1R endocytosis, failed to stimulate ERK1/2 activity. Inhibition of PTH1R endocytosis by K44A-dynamin dampened ERK1/2 activation in response to PTH-(1-34) by 69%. Incubation with the epidermal growth factor receptor inhibitor AG1478 reduced ERK1/2 phosphorylation further. In addition, ERK1/2 phosphorylation occurred following internalization of a PTH1R mutant induced by PTH-(7-34) in the absence of G protein signaling. Collectively, these data indicate that PTH1R trafficking and G(q) (but not G(s)) signaling independently contribute to ERK1/2 activation, predominantly via transactivation of the epidermal growth factor receptor.

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    • "Mechanisms accounting for PTH and PTHrP binding and activation of PTH1R have been widely investigated and support a two-site model involving initial rapid binding of the peptide C-terminal region (AAs 23-34) to the PTH1R N terminus, followed by a slower interaction of the peptide N terminus (AAs 1-14) with the J-domain containing transmembrane a-helices and interconnecting extracellular loops (Gardella and Jüppner, 2001; Castro et al., 2005; Gensure et al., 2005). Activation of PTH1R leads to regulation of multiple signaling pathways, including G s /adenylyl cyclase/cAMP/protein kinase A (PKA)-(Abou- Samra et al., 1992), G q/11 /phospholipase Cb/calcium/protein kinase C (PKC)-(Abou-Samra et al., 1992), and G 12/13 /Ras homolog gene family, member A/phospholipase D-signaling (Wang and Stern, 2010), as well as G protein–dependent and G protein – independent and b-arrestin – dependent activation of extracellular signal - related kinase ( ERK ) 1 / 2 ( Syme et al., 2005 ; Gesty - Palmer et al., 2006 ). PTH1R-mediated activation of PKC also occurs through a phospholipase Cb ( PLCb ) - independent mechanism ( Takasu et al. , 1999 ) . "
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    • "Indeed, this βarrestin mutant might inhibit or not PTHR1 internalization depending on the cell context (Sneddon and Friedman, 2007;Syme et al., 2005). In addition, βarrestin 319–418 blocks PTHinduced ERK activation (Syme et al., 2005). In OB-6 osteoblastic cells, we found that this dominant negative reverses the effect of endogenous βarrestin by conferring responsiveness to PTH in the absence of Cx43. "
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    • "In the case of b 2 -adrenergic receptor, the b-arrestin that binds to activated receptors recruits c-Src and initiates a second wave of signal transduction to activate ERK (Luttrell et al. 1999). While some GPCRs activate ERKs in an endocytosis-dependent manner, like the b 2 adrenergic receptor, activation of ERKs by some other GPCRs is independent of receptor internalization (Budd et al. 1999; DeGraff et al. 1999; Vogler et al. 1999; Shah et al. 2002; Syme et al. 2005). Stimulation of endogenous H2R in hippocampal CA3 pyramidal cells has been shown to activate ERK (Giovannini et al. 2003). "
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