Activation of FP prostanoid receptor isoforms leads to Rho-mediated changes in cell morphology and in the cell cytoskeleton.

Prostaglandin F(2alpha) (PGF(2alpha)) exerts its biological effects by binding to and activating FP prostanoid receptors. These receptors, which include two isoforms, the FP(A) and FP(B), have been cloned from a number of species and are members of the superfamily of G-protein-coupled receptors. Previous studies have shown that the activation of FP receptors leads to phosphatidylinositol hydrolysis, intracellular calcium release, and activation of protein kinase C. Here, we demonstrate that PGF(2alpha) treatment of 293-EBNA (Epstein-Barr nuclear antigen) cells that have been stably transfected with either the FP(A) or FP(B) receptor isoforms leads to changes in cell morphology and in the cell cytoskeleton. Specifically, cells treated with PGF(2alpha) show retraction of filopodia and become rounded, and actin stress fibers are formed. Pretreatment of the cells with bisindolylmaleimide I, a protein kinase C inhibitor, has no effect on the PGF(2alpha)-induced changes in cell morphology, although it does block the effects of phorbol myristate acetate on cell morphology. On the other hand, the PGF(2alpha)-induced changes in cell morphology and formation of actin stress fibers can be blocked by pretreatment of the cells with C3 exoenzyme, a specific inhibitor of the small G-protein, Rho. Consistent with FP receptor induced formation of actin stress fibers and focal adhesions, FP(A) receptor activation also leads to rapid (within two minutes) tyrosine phosphorylation of p125 focal adhesion kinase (FAK) which can be blocked by pretreating the cells with C3 exoenzyme. Taken together, these results suggest that the FP receptor isoforms are coupled to at least two second messenger pathways, one pathway associated with protein kinase C activation, and the other with activation of Rho.


Determination of the functional domain of a mouse autonomous replicating sequence.

We previously isolated from mouse cells an autonomous replicating sequence (ARS) ARS65 (Ariga, Itani and Iguchi-Ariga, Mol. Cell. Biol. 7, 1-6, 1987). Here we report the nucleotide sequence of ARS65. The sequence from BgIII to EcoRI sites cloned as ARS was 2658 bp long. There exist three interesting domains: a TA repeat, a myc like box (essential sequence for c-myc ARS), and a T rich region. Cloned DNAs containing various segments of pARS65 were transfected to rat 3Y1 cells together with the hygromycinB resistance expression vector, and hygromycinB resistant clones were isolated. Established cell lines transfected with plasmids carrying either a myc-like box or a T rich region harbored the replicated plasmids, indicating that these two elements are necessary for the ARS function of pARS65.


Stimulatory roles of muscarinic acetylcholine receptors on T cell antigen receptor/CD3 complex-mediated interleukin-2 production in human peripheral blood lymphocytes.

It is known that there are some bidirectional interactions between the nervous and the immune systems via neurotransmitters and cytokines. To clarify whether any neurotransmitters modulate lymphocyte functions, we examined the effects of oxotremorine-M (Oxo-M) on interleukin-2 (IL-2) production in human peripheral blood lymphocytes by using enzyme-linked immunosorbent assays, Northern blot analyses, reverse transcriptase-polymerase chain reaction, and fluorescence-activated cell sorter. Pretreatment of cells with Oxo-M (10 nM to 10 microM) for 4-24 hr enhanced phytohemagglutinin (PHA)-induced IL-2 mRNA expression and markedly increased IL-2 production compared with those induced by PHA alone. Oxo-M alone did not affect IL-2 mRNA expression and IL-2 production. In CD3-positive T cells, pretreatment with Oxo-M for 24 hr enhanced PHA-induced IL-2 production. Furthermore, pretreatment with Oxo-M enhanced PHA-induced mRNA expression of the alpha and beta subunits of IL-2 receptors and DNA synthesis. Cytometric analysis showed Oxo-M treatment did not up-regulate expression of cell surface molecules such as CD3, CD2, CD4, CD8, and IL-2 receptors. These results suggest that activation of muscarinic receptors enhances T cell antigen receptor/CD3-induced IL-2 production.


PARP14 regulates EP4 receptor expression in human colon cancer HCA-7 cells.

E type prostanoid 4 (EP4) receptors and their signaling pathways have been implicated in the development and malignant transformation of colorectal cancer. We herein demonstrated that the mono(ADP-ribosyl)ation of histone deacetylase (HDAC)1 and HDAC2 by poly(ADP-ribose) polymerase 14 (PARP14) may be required to induce the expression of EP4 receptors. The suppression of PARP14 activity by siRNA and/or its inhibitors reduced the mRNA expression of EP4 receptors. Thus, the expression of their proteins to approximately 50-80% in human colon cancer HCA-7 cells, however, which retained the activities of EP4 receptors to some extent. Since the expression levels of EP4 receptors are important factors for the maintenance of homeostasis, the adequate inhibition of PARP14 activity will be a good target for the prevention of colon cancer and/or as an alternative therapy for this disease. Since non-steroidal anti-inflammatory drugs (NSAIDs) are associated with a risk of heart attacks and stroke, novel PARP14 inhibitors will supersede NSAIDs without causing heart attacks and stroke, while maintaining appropriate EP4 receptor-mediated intestinal homeostasis.

Biochemical and Biophysical Research Communications


Anti-cancer effects of MW-03, a novel indole compound, by inducing 15-hydroxyprostaglandin dehydrogenase and cellular growth inhibition in the LS174T human colon cancer cell line

Increases in the expression of prostaglandin E (PGE) are widely known to be involved in aberrant growth in the early stage of colon cancer development. We herein demonstrated that the novel indole compound MW-03 reduced PGE-induced cAMP formation by catalization to an inactive metabolite by inducing 15-hydroxyprostaglandin dehydrogenase through the activation of peroxisome proliferator-activated receptor-γ. MW-03 also inhibited colon cancer cell growth by arresting the cell cycle at the S phase. Although the target of MW-03 for cell cycle inhibition has not yet been identified, these dual anti-cancer effects of MW-03 itself and/or its leading compound(s) on colon cancer cells may reduce colon cancer development and, thus, have potential as a novel treatment for the early stage of this disease.


Human EP2 prostanoid receptors exhibit more constraints to mutations than human DP prostanoid receptors.

Human D-type prostanoid (DP) and E-type prostanoid 2 (EP2) receptors are regarded as the most closely related receptors among prostanoid receptors. Although these receptors are generated by tandem duplication, their physiological outputs often oppose one another. In the present study, we extracted mutations occurring in the coding regions of both receptors using the 1000 genome project database and found that EP2 receptors have 8-fold fewer amino acid mutations. We speculate that EP2 receptors exhibit more constraints to mutations than DP receptors.


Indomethacin decreases arachidonic acid uptake in HCA-7 human colon cancer cells.

Nonsteroidal anti-inflammatory drugs (NSAIDs) reduce the incidence of colorectal cancer. However, evidence is accumulating that NSAIDs have anti-cancer effects in addition to inhibiting cyclooxygenase (COX)-mediated prostanoid biosynthesis. We now show that indomethacin, a popular NSAID, significantly reduced the [3H]-arachidonic acid uptake in HCA-7 human colon cancer cells. Interestingly, no decrease in the uptake of [3H]-arachidonic acid occurred when the cells were treated with aspirin, diclofenac, and sulindac even though the concentrations of these NSAIDs were high enough to inhibit COX-2 activity. These findings suggest that indomethacin has a novel anti-cancer effect that may be independent of COX-2 inhibition.


Human EP3(I) prostanoid receptor induces VEGF and VEGF receptor-1 mRNA expression.

A critical event in tumor development is the formation of new blood vessels to provide oxygen, nutrients and growth factors to the rapidly growing cancer cells. This process of angiogenesis is complex, however, it is well established that vascular endothelial growth factor (VEGF)-mediated signaling is an important early event. Knockout mice studies have implicated the EP3 receptor in tumor development and angiogenesis; however, the signaling mechanism involved with this effect is unclear. We now show that stimulation of the EP3(I) isoform of the human EP3 receptor with prostaglandin E(2) increases the mRNA expression of both VEGF and its cognate receptor VEGF receptor-1 (VEGFR-1). These inductions by the EP3(I) receptor involve the sequential activation of phosphatidylinositol 3-kinase and the extracellular signal-regulated kinases. Up-regulation of VEGF and VEGFR-1 mRNA by the human EP3(I) receptor has not been previously reported and further strengthen the role of this receptor in tumor-associated angiogenesis.


Indomethacin decreases EP2 prostanoid receptor expression in colon cancer cells.

Nonsteroidal anti-inflammatory drugs (NSAIDs) can decrease the risk of colorectal cancer; however, it has not been established if this effect is solely through their ability to inhibit cyclooxygenase (COX). In this study the effects of indomethacin, a potent NSAID and nonselective COX inhibitor, was examined in LS174T human colon cancer cells. These cells were found to express EP2 prostanoid receptors, but not the EP1, EP3 or EP4 subtypes. Pretreatment of LS174T cells with indomethacin produced a complete inhibition of prostaglandin E(2) (PGE(2)) stimulated cyclic AMP (cAMP) formation in a dose dependent manner with an IC(50) of 21 microM. Interestingly, the inhibition of PGE(2)-stimulated cAMP formation by indomethacin was accompanied by a decrease in EP2 mRNA expression and by a decrease in the whole cell specific binding of [(3)H]PGE(2). Thus, treatment of LS174T cells with indomethacin causes a down regulation of EP2 prostanoid receptors expression that may be independent of COX inhibition.


Prostaglandin F2alpha amplifies tumor necrosis factor-alpha promoter activity by the FPB prostanoid receptor.

This study examines the regulation of tumor necrosis factor-alpha (TNF-alpha) promoter activity by prostaglandin F2alpha ( PGF2alpha ) in HEK cells stably expressing either the FPA or FPB prostanoid receptors. Cells were transiently transfected with a luciferase reporter plasmid under the control of a TNF-alpha promoter and luciferase activity was measured. In the absence of PGF2alpha basal TNF-alpha reporter gene activity is elevated in FPB cells as compared with FPA cells. This elevated basal activity is blocked by pretreatment with a Rho inhibitor, but not by pretreatment with an inhibitor of protein kinase C (PKC). TNF-alpha reporter activity in FPB cells is stimulated by PGF2alpha and this is decreased by pretreatment with a chelator of intracellular calcium or by a gap junction inhibitor. In FPB cells pretreatment with a Rho inhibitor combined with either a calcium chelator or a gap junction inhibitor decreases both basal and PGF2alpha stimulated TNF-alpha reporter activity. Interestingly post-treatment of FPB cells with an inhibitor of PKC decreased PGF2alpha stimulated TNF-alpha reporter gene activity even though pretreatment did not. It, therefore, appears that PGF2alpha stimulated TNF-alpha reporter activity in FPB cells is amplified by a Rho-dependent mechanism involving calcium, gap junctions, and PKC. These findings may help in understanding the function of the FPB isoform in the corpus luteum.


Prostaglandin F2α stimulation of cyclooxygenase-2 promoter activity by the FPB prostanoid receptor.

We have recently shown that the FP(B) prostanoid receptor activates beta-catenin signaling through the activation of Rho in human embryo kidney (HEK)-293 cells stably expressing the FP(B) receptors. We now report that the FP(B) receptor can stimulate cyclooxygenase-2 promoter activity and may, therefore, regulate the expression of cyclooxygenase-2. This stimulation of cyclooxygenase-2 promoter activity is blocked by pretreatment with an inhibitor of Rho, but not with an inhibitor of protein kinase C (PKC). Potential up regulation of cyclooxygenase-2 expression by the FP(B) receptor would establish a positive feedback loop that would drive beta-catenin signaling and could be involved in cancer.


FP prostanoid receptor activation of a T-cell factor/beta -catenin signaling pathway.

FP prostanoid receptors are G-protein-coupled receptors (GPCR) that consist of two known isoforms, FP(A) and FP(B). These isoforms, which are generated by alternative mRNA splicing, are identical except for their carboxyl-terminal domains. Previously we have shown that stimulation of both isoforms with prostaglandin F(2alpha) (PGF(2alpha)) activates the small G-protein Rho, leading to morphological changes consisting of cell rounding and the formation of cell aggregates. Following the removal of PGF(2alpha), however, FP(A)-expressing cells show rapid reversal of cell rounding, whereas FP(B)-expressing cells do not. We now show that acute treatment of FP(B)-expressing cells with PGF(2alpha) leads to a subcellular reorganization of beta-catenin, a decrease in the phosphorylation of cytoplasmic beta-catenin, and persistent stimulation of Tcf/Lef-mediated transcriptional activation. This does not occur in FP(A)-expressing cells and may underlie the differences between these isoforms with respect to the reversal of cell rounding. The Tcf/beta-catenin signaling pathway is known to mediate the actions of Wnt acting through the heptahelical receptor, Frizzled, and has not been associated previously with GPCR activation. Our findings expand the signaling possibilities for GPCRs and suggest novel roles for FP receptors in normal tissue development and malignant transformation.