Serotonin-dependent collagenase transcription in myometrial cells requires extended AP-1 site

The 2G single nucleotide polymorphism (SNP) in the MMP-1 promoter contributes to high levels of MMP-1 transcription in MCF-7/ADR breast cancer cells

Degradation of stromal collagens in the extracellular matrix is mediated largely by matrix metalloproteinase-1 (MMP-1; collagenase-1), and high constitutive levels of MMP-1 in breast cancer correlate with a poor prognosis and invasive disease. MMP-1 expression is, in part, controlled by the mitogen-activated protein kinase (MAPK) pathway(s), which may target several activator protein-1 (AP-1) and polyoma enhancing activity-3/E26 virus (PEA3/ETS) sites within the promoter. An additional ETS site in the MMP-1 promoter is conferred by a single nucleotide polymorphism (SNP) at -1607 bp, when two guanines (5'-GGAT-3'; '2G allele/SNP') are present instead of one guanine (5'-GAT-3'; '1G allele/SNP'). This SNP is adjacent to an AP-1 site at -1602 bp, and in the presence of the 2G allele (ETS site), these sites cooperate to induce higher levels of transcription. ERK 1/2 is one component of the MAPK pathway and is constitutively active in MCF-7/ADR breast cancer cells, which are 1G/2G heterozygotes. This study demonstrates that when these cells are treated with PD098059, an ERK-specific inhibitor, MMP-1 mRNA levels are significantly decreased, suggesting that high constitutive expression of MMP-1 in these cells results from continuous ERK 1/2 activation. Using transient transfection, we determined that this signaling pathway targets different AP-1/ETS sites, depending upon which allele is present. Furthermore, in these cells, the AP-1 site at -1602 bp enhances transcription in the presence of the 2G SNP, but represses transcription from the 1G SNP. Finally, inhibiting ERK signaling and MMP-1 expression blocks type I collagen degradation and reduces the invasive ability of the MCF-7/ADR cells. We conclude that ERK 1/2 signaling and the 2G SNP mediate high levels of MMP-1 expression, which may contribute to the invasive potential of these breast cancer cells.

Activation of GATA-4 by serotonin in pulmonary artery smooth muscle cells

Serotonin (5-hydroxytryptamine (5-HT)) is a mitogen of pulmonary artery smooth muscle cells (PASMC) and plays an important role in the development of pulmonary hypertension. Signal transduction initiated by 5-HT involves serotonin transporter-dependent generation of reactive oxygen species and activation of the MEK-ERK pathway. However, the downstream transcriptional regulatory components have not been identified. In systemic smooth muscle cells, GATA-6 has been shown to regulate mitogenesis by driving cells into a quiescent state, and the down-regulation of GATA-6 induces mitogenesis. Thus, the present study tested the hypothesis that 5-HT induces mitogenesis of PASMC by down-regulating GATA-6. Quiescent bovine PASMC were treated with 5-HT, and the binding activity of nuclear extracts toward GATA DNA sequence was monitored. Surprisingly, PASMC express GATA-4, and 5-HT up-regulates the GATA DNA binding activity. Pretreatment of cells with inhibitors of serotonin transporter, reactive oxygen species, and MEK blocks GATA-4 activation by 5-HT. GATA-4 is not activated when the ERK phosphorylation site is mutated, indicating that 5-HT phosphorylates GATA-4 via the MEK/ERK pathway. GATA up-regulation is also induced by other mitogens of PASMC such as endothelin-1 and platelet-derived growth factor. Dominant negative mutants of GATA-4 suppress cyclin D2 expression and cell growth, indicating that GATA-4 activation regulates PASMC proliferation. Thus, GATA-4 mediates 5-HT-induced growth of PASMC and may be an important therapeutic target for the prevention of pulmonary hypertension.

Serotonin-induced MMP-13 production is mediated via phospholipase C, protein kinase C, and ERK1/2 in rat uterine smooth muscle cells

Serotonin (5-hydroxytryptamine; 5-HT), acting via the 5-HT(2A) receptor, up-regulates the transcription and production of interstitial collagenase (matrix metalloproteinase-13; MMP-13), a critical enzyme responsible for maintaining the integrity of the uterus, after parturition. Serotonin treatment of rat uterine myometrial smooth muscle cells induced inositol phosphate (IP) turnover, which was abolished by the 5-HT(2A) receptor-specific antagonists ketanserin and spiperone. The phospholipase C (PLC) inhibitors and D609 attenuated serotonin-mediated-IP turnover with a corresponding inhibition of MMP-13 protein production. Subsequent recovery of both MMP-13 protein expression and IP generation was seen following the removal of D609. Protein kinase C (PKC) activators, the diacylglycerol analogue 1,2-dioctanoyl-sn-glycerol and phorbol myristate acetate (PMA), mimicked the effect of serotonin on MMP-13 protein expression; prolonged PMA treatment (which down-regulates PKC) lowered MMP-13 protein levels. The PKC-specific inhibitors bisindolylmaleimide I, calphostin C, CGP 41251, and the PKCdelta-selective inhibitor rottlerin were able to suppress serotonin up-regulation of MMP-13. Furthermore, the mitogen-activated protein kinase kinase (MEK) inhibitor PD98059 blocked serotonin-dependent activation of p44/42 MAPK (pERK1/2), a downstream effector of PKC and also down-regulated MMP-13 protein expression. Similarly, calphostin C and rottlerin depressed activation of p44/42 MAPK. From these studies, serotonin, binding through the 5-HT(2A) receptor, initiates a signaling cascade whereby stimulation of PLC leads to the activation of PKC and subsequently the ERK1/2 pathway, which ultimately results in MMP-13 production.