Serotonin-mediated 5-HT 2 receptor gene regulation in rat myometrial smooth muscle cells

Abstract

Serotonin (5-hydroxytryptamine; 5-HT) has recently been shown to induce collagenase production in myometrial smooth muscle cells (Jeffrey et al. (1991) J. Cell. Physiol. 146, 399–406) by activating transcription of the collagenase gene (Wilcox et al. (1992) J. Biol. Chem. 267, 20752–20757) following an interaction with the 5-HT 2 receptor (Rydelek-Fitzgerald et al. (1993) Mol. Cell. Endocrinol. 91, 67–74). These studies were performed to investigate factors controlling the regulation of 5-HT 2 receptors in these cells. Northern blot analysis indicates that serotonin increases levels of 5-HT 2 receptor mRNA in cells by approximately 4-fold. Detectable increases in mRNA levels occur within 2 h after administration of serotonin with maximal levels occurring after 12 h. The 5-HT 2 receptor antagonists, ketanserin and spiperone, inhibit the serotonin-mediated increase in receptor mRNA. Selective 5-HT 2 receptor agonists ((±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (DOI) and quipazine) mimic the effect of serotonin, whereas 5-HT 1 and 5-HT 3 receptor agonists ((±)-8-hydroxydipropylaminotetralin (8-OH-DPAT), 1-(3-chlorophenyl)piperazine dihydrochloride (mCPP), m-phenylbiguanide) have no effect. These data demonstrate that serotonin induces an increase in 5-HT 2 receptor mRNA by interacting with the 5-HT 2 receptor itself. Nuclear run-on analysis revealed that serotonin increases the initiation of 5-HT 2 receptor mRNA synthesis. Moreover, the protein synthesis inhibitor, cycloheximide, prevents the induction of the mRNA for the receptor, demonstrating that serotonin-dependent increases in 5-HT 2 receptor transcription require de novo protein synthesis. Medroxyprogesterone acetate, an inhibitor of collagenase gene activation (Wilcox et al. (1992) J. Biol. Chem. 267, 20752–20757), has no effect on 5-HT 2 receptor mRNA levels. Scatchard analyses with [ 125I]LSD (2-[ 125I]iodo-lysergic acid diethylamide) reveal that steady-state levels of 5-HT 2 receptors are not altered after 5 days of treatment with serotonin. The contrast between mRNA levels and receptor densities suggests that 5-HT 2 receptor turnover may be increased by serotonin or other mechanisms may be in place to maintain a constant level of 5-HT 2 receptors in myometrial smooth muscle cells.