1. Department of Medicine, Stanford University School of Medicine, and VA Palo Alto Health Care System, Palo Alto, CA, U.S.A.
2. ^*Department of Dermatology, University of California Davis, School of Medicine, CA, 95616, U.S.A.

Correspondence: Rivkah Isseroff, MD, Department of Dermatology, Dermatology Research, TB 192, One Shields Avenue, University of California Davis School of Medicine, Davis, CA 95616, U.S.A. Email: rrisseroff@ucdavis.edu

¹Present address: FDA/CDER, HFD-160, 5600 Fishers Lane, Rockville, Maryland

Received 6 December 2001; Revised 24 June 2002; Accepted 8 August 2002.

Abstract

There is increasing evidence that G-protein-coupled receptors cross-talk with growth factor receptor-mediated signal transduction in a variety of cell types. We have investigated mechanisms by which the activation of -adrenergic receptors, classically GTP-binding proteins coupled receptors, influence the migration of cultured human keratinocytes. We found that iso-proterenol, a -adrenergic receptor-selective agonist, inhibited cell migration stimulated by either epidermal growth factor, or extracellular Ca²⁺ in a concentration-dependent manner. This was prevented by pretreatment of the cells with the -adrenergic receptor-selective antagonist timolol. Interestingly, isoproterenol, at a concentration of 1 nM, did not measurably increase intracellular cyclic adenosine monophosphate concentrations yet inhibited cell migration by 50%. To test further if isoproterenol's actions were mediated via activation of adenylyl cyclase, two inhibitors of its activity, 2'5'-dideoxyadenosine and SQ22536, were used. Both compounds significantly diminished iso-proterenol-induced increases in intracellular cyclic adenosine monophosphate concentrations but did not attenuate isoproterenol-induced inhibition of cell migration. Also, forskolin (1 M) markedly increased intracellular cyclic adenosine monophosphate concentrations but did not significantly inhibit cell migration. As mitogen-activated protein kinases are known to signal growth factor-stimulated cell migration, we examined whether -adrenergic receptor-mediated inhibition of keratinocyte migration might occur via inactivation of mitogen-activated protein kinases. We found that isoproterenol inhibited phosphorylation of extracellular signal-regulated kinase mitogen-activated protein kinase in a concentration-dependent manner but had no effect on the phosphorylation of the stress mitogen-activated protein kinases c-jun N-terminal kinase and stress-activated protein kinase-2. Neither forskolin nor a membrane permeable cyclic adenosine monophosphate analog inhibited phosphorylation of any of these mitogen-activated protein kinases. These findings suggest that -adrenergic receptor-induced inhibition of keratinocyte migration is mediated through inhibition of the extracellular signal-regulated kinase mitogen-activated protein kinase signaling in a cyclic adenosine monophosphate-independent manner.