5-Hydroxytryptamine 2B receptor regulates cell-cycle progression: Cross-talk with tyrosine kinase pathways

Abstract

In this paper, we present evidence that activation of 5-hydroxytryptamine 2B (5-HT2B) receptors by serotonin (5-HT) leads to cell-cycle progression through retinoblastoma protein hyperphosphorylation and through activation of both cyclin D1͞cdk4 and cyclin E͞cdk2 kinases by a mechanism that depends on induction of cyclin D1 and cyclin E protein levels. The induction of cyclin D1 expression, but not that of cyclin E, is under mitogen-activated protein kinase (MAPK) control, indicating an independent regulation of these two cyclins in the 5-HT2B receptor mitogenesis. Moreover, by using the specific platelet-derived growth factor receptor (PDGFR) inhibitor AG 1296 or by overexpressing a kinasemutant PDGFR, we show that PDGFR kinase activity is essential for 5-HT2B-triggered MAPK͞cyclin D1, but not cyclin E, signaling pathways. 5-HT2B receptor activation also increases activity of the cyclins D1 and E ͉ G protein-coupled receptors ͉ platelet-derived growth factor receptor ͉ receptor signaling ͉ c-Src S erotonin (5-hydroxytryptamine, 5-HT) is involved in regulating cellular functions of central and peripheral nervous systems, endocrine and exocrine organs, as well as vascular and hematopoietic systems (1). These actions are mediated by numerous cognate receptors. For instance, 5-HT acts as a growth factor in a variety of cells, a function that is mediated by 5-HT1A, 5-HT1B, 5-HT2A, 5-HT2B, or 5-HT2C receptor subtypes (2-5). The 5-HT2B receptor belongs to the G protein-coupled receptor (GPCR) family. Binding of 5-HT to 5-HT2B receptor activates G q protein, thereby stimulating phospholipase C, which initiates a rapid release of inositol trisphosphate and results in a rise in intracellular calcium levels (6). The signal transduction pathways activated downstream of the 5-HT2B receptor include the Ras and mitogen-activated protein kinase (MA PK of the MAPK͞ERK subfamily) pathways (3). Despite numerous studies of 5-HT signal transduction pathways, the critical steps from signal integration to its proliferative action have not been elucidated.The regulation of cell proliferation is a complex process controlled by external mitogenic factors. Once cells are induced to proliferate, passage through the mitotic cell cycle is directed by activation of a series of cyclins and their catalytic subunits, cyclin-dependent kinases (cdks) (7). Mitogenic factors act by stimulating both the proliferation of quiescent cells arrested in G 0 and the progression of the cell cycle through the restriction point in late G 1 . Progression through G 1 and the G 1 ͞S transition in mammalian cells is regulated by cdk4 and cdk6, which form complexes with cyclin D1, and by cdk2, which forms a complex with cyclin E (7). The G 1 cyclin͞cdk complexes drive the phosphorylation of retinoblastoma protein (pRb) that represents the limiting event in G 1 progression (8). However, the mechanism whereby 5-HT triggers G 1 progression has not been examined.The link between upstream signaling circuitry and the cellcycle machinery is of interest. Identified candid...

Signaling Pathways Transduced through the Elastin Receptor Facilitate Proliferation of Arterial Smooth Muscle Cells

“…Our observation, that the elastin peptide-induced signaling pathway includes activation of G protein and consecutive phosphorylation of 60-kDa c-Src, seems to be consistent with the report of Nebigil and colleagues (73) who demonstrated that c-Src plays an upstream role in the trans-activation of the PDGF receptor in the mitogenic signaling propagated by the G protein-coupled receptor interacting with 5-hydroxytryptamine. The possibility of the interaction vice versa was excluded by the fact that inactivation of PDGF receptor kinase by AG1295 did not diminish phosphorylation of 60-kDa c-Src induced by elastin peptides (Fig.…”

Serotonin 2B receptor is required for heart development

“…Whole-mount immunohistochemical staining of embryos for developing blood vessels with antiplatelet endothelial cell adhesion molecule (PharMingen 01951D) antibody were performed as described (11). Western blot analysis for ErbB-2 and platelet-derived growth factor receptor-␤ (SC-432) was performed in the whole embryo or cell lysate as described (16).…”

“…Thymidine incorporation was detected in cardiomyocytes as described (16). Briefly, quiescent cells (24-h serum starved) were treated with 5-HT (1 M) or neuregulin (heregulin) (25 g͞ml) for 16 h, and 0.5 mCi of [ 3 H]thymidine was added to the culture during the last 4 h of incubation.…”

“…Recently, this receptor has been shown to activate the phospholipase A2 (13) and nitric oxide synthases (14) in transfected and endogenously 5-HT 2B -expressing cells. Agonist stimulation of 5-HT 2B receptor subtype also causes a rapid and transient activation of the protooncogene product p21 ras (15) and p42 mapk ͞p44 mapk mitogen-activated protein kinases and transduces a mitogenic signal by activating the nonreceptor tyrosine kinase c-Src and the receptor tyrosine kinase platelet-derived growth factor receptor (16) in mouse fibroblast cells. 5-HT 2B receptor expression has been shown to induce tumors in nude mice and has been detected at a high level in human carcinoid tumors (15).…”

Modulation of Serotonergic Receptor Signaling and Cross-talk by Prion Protein*

“…5-HT binding to either 5-HT 2 subclass activates G q protein and stimulates phospholipase C (PLC␤), thereby initiating a rapid release of inositol 1,4,5-trisphosphate (IP 3 ) and a rise in intracellular calcium level (6). The 5-HT 2B receptor is also coupled to the ras/mitogen-activated protein kinase cascade (7) and cross-talks with tyrosine kinase pathways to promote cell proliferation (8). In addition, the 5-HT 2B receptor recruits both cellular and inducible nitric-oxide (NO) synthase (NOS) transduction pathways through a type I PDZ domain (9).…”