1B- and 1D-Adrenergic Receptors Exhibit Different Requirements for Agonist and Mitogen-Activated Protein Kinase Activation to Regulate Growth Responses in Rat 1 Fibroblasts

We compared DNA replication, protein biosynthesis, and mitogen-activated protein kinase (MAPK) activity in Rat 1 fibroblasts stably expressing either the 1B-adrenergic receptor (AR) or 1D-AR subtypes. Activation of both the 1B-AR and 1D-AR inhibited DNA synthesis (as assessed by [H]thymidine incorporation). In contrast, both receptors stimulated protein biosynthesis (as measured by [S]methionine incorporation) and activated extracellular signal-regulated kinase (ERK)1/2. Importantly, these responses were agonist-dependent for the 1B-AR, but were agonist-independent for the 1D-AR. Agonist activation of the 1B-AR resulted in increased p38 kinase activity, but not c-Jun NH2-terminal kinase (JNK) activity, whereas the 1D-AR activated JNK but not p38 kinase. Unlike ERK1/2, JNK activity was increased by agonist treatment in the 1D-AR cells. An ERK1/2-pathway inhibitor PD98059 had no effect on phenylephrine-mediated inhibition of DNA synthesis in either cell line but blocked protein biosynthesis mediated by both receptors. The p38 kinase inhibitor SB203580 blocked 1B-AR effects on [H]thymidine and [S]methionine incorporation in 1B-AR-expressing cells, but had no effect on 1D-AR-mediated growth responses, consistent with the inability of the 1D-AR to activate p38 kinase. Therefore, 1Band 1D-ARs mediated similar growth responses but differ with respect to the MAPK family member involved and the requirement for agonist. Three genes encoding unique 1-AR subtypes, 1A-, 1B-, or 1D-AR, have been cloned and pharmacologically characterized (Cotecchia et al., 1988; Schwinn et al., 1990; Lomasney et al., 1991; Perez et al., 1991; Hieble et al., 1995). All three 1-AR subtypes exhibit similar affinity for endogenous catecholamines (Schwinn et al., 1990; Lomasney et al., 1991; Perez et al., 1991); however, the cellular functions of these receptors have not been adequately defined. Our previous work showed that although all receptor subtypes are expressed in peripheral arteries, the 1A-AR or 1D-AR couple agonist binding to smooth muscle contraction in a given vessel (Guarino et al., 1996; Hrometz et al., 1999; Piascik and Perez, 2001). In addition to the acute regulation of blood pressure, catecholamines induce vascular smooth muscle cell growth (Johnson et al., 1983; deBlois et al., 1996; Fingerle et al., 1991; van Kleef et al., 1992; Chen et al., 1995). These observations suggest that expressed 1-AR subtypes may differentially activate signaling pathways and physiological