SEROTONIN-MEDIATED 5-HT2 RECEPTOR GENE-REGULATION IN RAT MYOMETRIAL SMOOTH-MUSCLE CELLS

Serotonin (5-hydroxytryptamine; 5-HT) has recently been shown to induc e collagenase production in myometrial smooth muscle cells (Jeffrey et al. (1991) J. Cell. Physiol. 146, 399-406) by activating transcriptio n of the collagenase gene (Wilcox et al. (1992) J. Biol. Chem. 267, 20 752-20757) following an interaction with the 5-HT2 receptor (Rydelek-F itzgerald et al. (1993) Mol. Cell. Endocrinol. 91, 67-74). These studi es were performed to investigate factors controlling the regulation of 5-HT2 receptors in these cells. Northern blot analysis indicates that serotonin increases levels of 5-HT2 receptor mRNA in cells by approxi mately 4-fold. Detectable increases in mRNA levels occur within 2 h af ter administration of serotonin with maximal levels occurring after 12 h. The 5-HT2 receptor antagonists, ketanserin and spiperone, inhibit the serotonin-mediated increase in receptor mRNA. Selective 5-HT2 rece ptor agonists +/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl ( DOI) and quipazine) mimic the effect of serotonin, whereas 5-HT, and 5 -HT3 receptor agonists ((+/-)-8-hydroxydipropylaminotetralin (8-OH-DPA T), 1-(3-chlorophenyl)piperazine dihydrochloride (mCPP), m-phenylbigua nide) have no effect. These data demonstrate that serotonin induces an increase in 5-HT2 receptor mRNA by interacting with the 5-HT2 recepto r itself. Nuclear run-on analysis revealed that serotonin increases th e initiation of 5-HT2 receptor mRNA synthesis. Moreover, the protein s ynthesis inhibitor, cycloheximide, prevents the induction of the mRNA for the receptor, demonstrating that serotonin-dependent increases in 5-HT2 receptor transcription require de novo protein synthesis. Medrox yprogesterone acetate, an inhibitor of collagenase gene activation (Wi lcox et al. (1992) J. Biol. Chem. 267, 20752-20757), has no effect on 5-HT2 receptor mRNA levels. Scatchard analyses with [I-125]LSD (2-[I-1 25]iodo-lysergic acid diethylamide) reveal that steady-state levels of 5-HT2 receptors are not altered after 5 days of treatment with seroto nin. The contrast between mRNA levels and receptor densities suggests that 5-HT2 receptor turnover may be increased by serotonin or other me chanisms may be in place to maintain a constant level of 5-HT2 recepto rs in myometrial smooth muscle cells.