Prostanoid receptor signaling relevant to tumor growth and angiogenesis

Targeting Arachidonic Acid Metabolism Enhances Immunotherapy Efficacy in ARID1A-Deficient Colorectal Cancer

AT-rich interactive domain-containing protein 1A (ARID1A), a core constituent of the switch/sucrose nonfermentable (SWI/SNF) complex, is mutated in approximately 10% of colorectal cancers. Whereas ARID1A deficiency corresponds to heightened immune activity in colorectal cancer, immune checkpoint inhibitors (ICI) have shown limited efficacy in these tumors. The discovery of targetable vulnerabilities associated with ARID1A deficiency in colorectal cancer could expand treatment options for patients. In this study, we demonstrated that arachidonic acid (AA) metabolism inhibitors synergize with ICIs in ARID1A-deficient colorectal cancer by enhancing the activity of CD8+ T cells and inhibiting vasculogenic mimicry. Epigenetic analysis using ATAC-seq and ChIP-qPCR revealed that the lack of ARID1A results in reduced levels of PTGS1 and PTGS2, the key enzymes that control the AA pathway. Low PTGS1 and PTGS2 expression generated a reliance on the remaining functionality of the AA pathway in ARID1A-deficient cells. The AA pathway inhibitor aspirin selectively inhibited the growth of ARID1A-deficient colorectal cancer, and aspirin sensitized tumors lacking ARID1A to immunotherapy. Together, these findings suggest that blocking AA metabolism can enhance immune responses against tumors by activating CD8+ T cells and inhibiting vasculogenic mimicry, which synergizes with ICIs to improve treatment of ARID1A-deficient colorectal cancer. Significance: The arachidonic acid pathway is a metabolic vulnerability in ARID1A-deficient colorectal cancer that can be targeted with aspirin to suppress tumor growth and enhance sensitivity to immunotherapy, providing a promising therapeutic strategy.

A biologically active lipid, thromboxane, as a regulator of angiogenesis and lymphangiogenesis

Thromboxane (TX) and prostaglandins are metabolites of arachidonic acid, a twenty-carbon unsaturated fatty acid, and have a variety of actions that are exerted via specific receptors. Angiogenesis is defined as the formation of new blood vessels from pre-existing vascular beds and is a critical component of pathological conditions, including inflammation and cancer. Lymphatic vessels play crucial roles in the regulation of interstitial fluid, immune surveillance, and the absorption of dietary fat from the intestine; and they are also involved in the pathogenesis of various diseases. Similar to angiogenesis, lymphangiogenesis, the formation of new lymphatic vessels, is a critical component of pathological conditions. The TP-dependent accumulation of platelets in microvessels has been reported to enhance angiogenesis under pathological conditions. Although the roles of some growth factors and cytokines in angiogenesis and lymphangiogenesis have been well characterized, accumulating evidence suggests that TX induces the production of proangiogenic and prolymphangiogenic factors through the activation of adenylate cyclase, and upregulates angiogenesis and lymphangiogenesis under disease conditions. In this review, we discuss the role of TX as a regulator of angiogenesis and lymphangiogenesis, and its emerging importance as a therapeutic target.

The 5-lipoxygenase/cyclooxygenase-2 cross-over metabolite, hemiketal E2, enhances VEGFR2 activation and promotes angiogenesis

Consecutive oxygenation of arachidonic acid by 5-lipoxygenase and cyclooxygenase-2 yields the hemiketal eicosanoids, HKE2 and HKD2. Hemiketals stimulate angiogenesis by inducing endothelial cell tubulogenesis in culture; however, how this process is regulated has not been determined. Here, we identify vascular endothelial growth factor receptor 2 (VEGFR2) as a mediator of HKE2-induced angiogenesis in vitro and in vivo. We found that HKE2 treatment of human umbilical vein endothelial cells dose-dependently increased the phosphorylation of VEGFR2 and the downstream kinases ERK and Akt that mediated endothelial cell tubulogenesis. In vivo, HKE2 induced the growth of blood vessels into polyacetal sponges implanted in mice. HKE2-mediated effects in vitro and in vivo were blocked by the VEGFR2 inhibitor vatalanib, indicating that the pro-angiogenic effect of HKE2 was mediated by VEGFR2. HKE2 covalently bound and inhibited PTP1B, a protein tyrosine phosphatase that dephosphorylates VEGFR2, thereby providing a possible molecular mechanism for how HKE2 induced pro-angiogenic signaling. In summary, our studies indicate that biosynthetic cross-over of the 5-lipoxygenase and cyclooxygenase-2 pathways gives rise to a potent lipid autacoid that regulates endothelial cell function in vitro and in vivo. These findings suggest that common drugs targeting the arachidonic acid pathway could prove useful in antiangiogenic therapy.

Biologically active lipids in the regulation of lymphangiogenesis in disease states

Lymphatic vessels have crucial roles in the regulation of interstitial fluids, immune surveillance, and the absorption of dietary fat in the intestine. Lymphatic function is also closely related to the pathogenesis of various disease states such as inflammation, lymphedema, endometriosis, liver dysfunction, and tumor metastasis. Lymphangiogenesis, the formation of new lymphatic vessels from pre-existing lymphatic vessels, is a critical determinant in the above conditions. Although the effect of growth factors on lymphangiogenesis is well-characterized, and biologically active lipids are known to affect smooth muscle contractility and vasoaction, there is accumulating evidence that biologically active lipids are also important inducers of growth factors and cytokines that regulate lymphangiogenesis. This review discusses recent advances in our understanding of biologically active lipids, including arachidonic acid metabolites, sphingosine 1-phosphate, and lysophosphatidic acid, as regulators of lymphangiogenesis, and the emerging importance of the lymphangiogenesis as a therapeutic target.

Roles of Thromboxane Receptor Signaling in Enhancement of Lipopolysaccharide-Induced Lymphangiogenesis and Lymphatic Drainage Function in Diaphragm

[Figure: see text].

CGRP/CGRP Receptor Antibodies: Potential Adverse Effects Due to Blockade of Neovascularization?

Migraine is a severe neurological disorder in which calcitonin gene-related peptide (CGRP) is a key molecule in pathophysiology. Neuronal system-derived CGRP enhances neovascularization in several important pathological conditions and sends a cue to the vascular system. In 2018, the FDA approved erenumab and fremanezumab, antibodies against CGRP receptor and CGRP, as the first new class of drugs for migraine. Treatment of migraine with these antibodies requires great care because neovascularization-related adverse effects may be induced in some patients. Here, we focus on enhancement of neovascularization by CGRP and discuss possible adverse effects resulting from blocking neovascularization. We also suggest that CGRP antibodies may also be used as novel antitumor agents by suppressing tumor-associated angiogenesis.

Prostate Cancer and Aspirin Use: Synopsis of the Proposed Molecular Mechanisms

Background: Prostate cancer (PCa) is a critical health burden, impacting the morbidity and mortality of millions of men around the world. Most of the patients with PCa have their disease at first sensitive to androgen deprivation treatments, but later they develop resistance to therapy and eventually die of metastatic castration-resistant prostate cancer (CRPC). Although the newly developed anti-androgen therapies are effectively alleviating symptoms and prolonging lives of patients, there are still no curable treatments for CRPC. Recently, statistical studies have shown that the chronic use of aspirin might be significantly associated with better outcomes in PCa patients. Through this review, we aim to identify the different proposed molecular mechanisms relating aspirin to the pathobiology of PCa neoplasms, with a major focus on basic research done in this context.

Methods: Articles were retrieved via online database searching of PubMed and MEDLINE between 1946 and September 2016. Keywords and combinations related to PCa and aspirin were used to perform the search. Abstracts of the articles were studied by two independent reviewers and then data extraction was performed on the relevant articles that met our review objectives.

Results: Aspirin, a non-steroidal anti-inflammatory drug (NSAID), affects the proliferation, apoptosis, resistance and metastasis of PCa cell lines, through both COX-dependent and COX-independent mechanisms. It also lowers levels of the PCa diagnostic marker prostate specific antigen (PSA), suggesting that clinicians need to at least be aware if their patients are using Aspirin chronically.

Conclusion: This review strongly warrants further consideration of the signaling cascades activated by aspirin, which may lead to new knowledge that might be applied to improve diagnosis, prognosis and treatment of PCa.

Signaling of Prostaglandin E Receptors, EP3 and EP4 Facilitates Wound Healing and Lymphangiogenesis with Enhanced Recruitment of M2 Macrophages in Mice

Lymphangiogenesis plays an important role in homeostasis, metabolism, and immunity, and also occurs during wound-healing. Here, we examined the roles of prostaglandin E₂ (PGE₂) receptor (EP) signaling in enhancement of lymphangiogenesis in wound healing processes. The hole-punch was made in the ears of male C57BL/6 mice using a metal ear punch. Healing process and lymphangiogenesis together with macrophage recruitment were analyzed in EP knockout mice. Lymphangiogenesis was up-regulated in the granulation tissues at the margins of punched-hole wounds in mouse ears, and this increase was accompanied by increased expression levels of COX-2 and microsomal prostaglandin E synthase-1. Administration of celecoxib, a COX-2 inhibitor, suppressed lymphangiogenesis in the granulation tissues and reduced the induction of the pro-lymphangiogenic factors, vascular endothelial growth factor (VEGF) -C and VEGF-D. Topical applications of selective EP receptor agonists enhanced the expressions of lymphatic vessel endothelial hyaluronan receptor-1 and VEGF receptor-3. The wound-healing processes and recruitment of CD11b-positive macrophages, which produced VEGF-C and VEGF-D, were suppressed under COX-2 inhibition. Mice lacking either EP3 or EP4 exhibited reduced wound-healing, lymphangiogenesis and recruitment of M2 macrophages, compared with wild type mice. Proliferation of cultured human lymphatic endothelial cells was not detected under PGE₂ stimulation. Lymphangiogenesis and recruitment of M2 macrophages that produced VEGF-C/D were suppressed in mice treated with a COX-2 inhibitor or lacking either EP3 or EP4 during wound healing. COX-2 and EP3/EP4 signaling may be novel targets to control lymphangiogenesis in vivo.

Downregulation of the proangiogenic prostaglandin E receptor EP3 and reduced angiogenesis in a mouse model of diabetes mellitus

Vascular complications such as foot ulcers are a hallmark of diabetes mellitus (DM), although the molecular mechanisms that underlie vascular dysfunction remain unclear. Herein, we show that angiogenesis, which is indispensable to the healing of ulcers, is suppressed in polyurethane sponge implants in mice with DM and reduced proangiogenic signaling. DM was induced in male C57BL/6 mice by intraperitoneal injection of streptozotocin (100mg/kg). Polyurethane sponge disks were implanted into subcutaneous tissues on the backs of mice, and angiogenesis and expression of related factors were analyzed in sponge granulation tissues. Densities of platelet endothelial cell adhesion molecule-1 (PECAM-1)-positive vascular structures and PECAM-1 expression in sponge granulation tissues were increased over time in control mice and reduced in diabetic mice. The reductions in diabetic mice were accompanied by reduced expression of inducible cyclo-oxygenase-2 and microsomal prostaglandin E synthase-1. The prostaglandin E receptor subtype EP3 was downregulated in sponge granulation tissues in diabetic mice, whereas EP1, EP2, and EP4 were not. The expression of the proangiogenic growth factor vascular endothelial growth factor (VEGF)-A and the chemokine stromal cell-derived factor-1 (SDF-1) were both reduced in diabetic mice. Treatment of diabetic mice with a selective agonist of EP3, ONO-AE 248 (30 nmol/site/day, topical injection), reversed suppression of angiogenesis in diabetic mice. These results indicate that proangiogenic EP3 signaling is suppressed in diabetic mice with reduced expression of VEGF and SDF-1. Stimulation of EP3 signaling restored angiogenesis in a sponge implant model in mice with DM. This suggests that topical application of an EP3 agonist could be a novel strategy to treat foot ulcers in patients with DM.

Nonsteroidal anti-inflammatory drugs and prostatic diseases

Prostatic diseases are characterized by increased activity of cytokines, growth factors, and cyclooxygenases- (COX-) 1 and 2. Activation of COX-1 and COX-2 results in increased levels of prostaglandins and the induction of angiogenic, antiapoptotic and inflammatory processes. Inhibition of COX enzymes by members of the widely used nonsteroidal anti-inflammatory drug (NSAID) class of drugs decreases prostaglandin production, and exerts a variety of anti-inflammatory, antipyretic, and antinociceptive effects. While numerous in vitro, in vivo, and clinical studies have shown that NSAIDs inhibit the risk and progression of prostatic diseases, the relationship between NSAIDs and such diseases remains controversial. Here we review the literature in this area, critically analyzing the benefits and caveats associated with the use of NSAIDs in the treatment of prostatic diseases.

Vascular endothelial growth factor receptor 1 signaling facilitates gastric ulcer healing and angiogenesis through the upregulation of epidermal growth factor expression on VEGFR1+CXCR4 + cells recruited from bone marrow

BACKGROUND

Angiogenesis is essential for gastric ulcer healing. Recent results suggest that vascular endothelial growth factor receptor 1 (VEGFR1), which binds to VEGF, promotes angiogenesis. In the present study, we investigated the role of VEGFR1 signaling in gastric ulcer healing and angiogenesis.

METHODS

Gastric ulcers were induced by serosal application of 100 % acetic acid in wild-type (WT) and tyrosine kinase-deficient VEGFR1 mice (VEGFR1 TK(-/-)). Bone marrow transplantation into irradiated WT mice was carried out using bone marrow cells isolated from WT and VEGFR1 TK(-/-) mice.

RESULTS

Ulcer healing was delayed in VEGFR1 TK(-/-) mice compared to WT mice and this was accompanied by decreased angiogenesis, as evidenced by reduced mRNA levels of CD31 and decreased microvessel density. Recruitment of cells expressing VEGFR1 and C-X-C chemokine receptor type 4 (CXCR4) was suppressed and epidermal growth factor (EGF) expression in ulcer granulation tissue was attenuated. Treatment of WT mice with neutralizing antibodies against VEGF or CXCR4 also delayed ulcer healing. In WT mice transplanted with bone marrow cells from VEGFR1 TK(-/-) mice, ulcer healing and angiogenesis were suppressed, and this was associated with reduced recruitment of bone marrow cells to ulcer granulation tissue. VEGFR1 TK(-/-) bone marrow chimeras also exhibited downregulation of EGF expression on CXCR4(+)VEGFR1(+) cells recruited from the bone marrow into ulcer lesions.

CONCLUSION

VEGFR1-mediated signaling plays a critical role in gastric ulcer healing and angiogenesis through enhanced EGF expression on VEGFR1(+)CXCR4(+) cells recruited from the bone marrow into ulcer granulation tissue.

Cyclooxygenase-2-prostaglandin E2-eicosanoid receptor inflammatory axis: a key player in Kaposi's sarcoma-associated herpes virus associated malignancies

The role of cyclooxygenase-2 (COX-2), its lipid metabolite prostaglandin E2 (PGE2), and Eicosanoid (EP) receptors (EP; 1-4) underlying the proinflammatory mechanistic aspects of Burkitt's lymphoma, nasopharyngeal carcinoma, cervical cancer, prostate cancer, colon cancer, and Kaposi's sarcoma (KS) is an active area of investigation. The tumorigenic potential of COX-2 and PGE2 through EP receptors forms the mechanistic context underlying the chemotherapeutic potential of nonsteroidal anti-inflammatory drugs (NSAIDs). Although role of the COX-2 is described in several viral associated malignancies, the biological significance of the COX-2/PGE2/EP receptor inflammatory axis is extensively studied only in Kaposi's sarcoma-associated herpes virus (KSHV/HHV-8) associated malignancies such as KS, a multifocal endothelial cell tumor and primary effusion lymphoma (PEL), a B cell-proliferative disorder. The purpose of this review is to summarize the salient findings delineating the molecular mechanisms downstream of COX-2 involving PGE2 secretion and its autocrine and paracrine interactions with EP receptors (EP1-4), COX-2/PGE2/EP receptor signaling regulating KSHV pathogenesis and latency. KSHV infection induces COX-2, PGE2 secretion, and EP receptor activation. The resulting signal cascades modulate the expression of KSHV latency genes (latency associated nuclear antigen-1 [LANA-1] and viral-Fas (TNFRSF6)-associated via death domain like interferon converting enzyme-like- inhibitory protein [vFLIP]). vFLIP was also shown to be crucial for the maintenance of COX-2 activation. The mutually interdependent interactions between viral proteins (LANA-1/vFLIP) and COX-2/PGE2/EP receptors was shown to play key roles in the biological mechanisms involved in KS and PEL pathogenesis such as blockage of apoptosis, cell cycle regulation, transformation, proliferation, angiogenesis, adhesion, invasion, and immune-suppression. Understanding the COX-2/PGE2/EP axis is very important to develop new safer and specific therapeutic modalities for KS and PEL. In addition to COX-2 being a therapeutic target, EP receptors represent ideal targets for pharmacologic agents as PGE2 analogues and their blockers/antagonists possess antineoplastic activity, without the reported gastrointestinal and cardiovascular toxicity observed with few a NSAIDs.

NSAID, aspirin delays gastric ulcer healing with reduced accumulation of CXCR4(+)VEGFR1(+) cells to the ulcer granulation tissues

BACKGROUND

Ulcer healing is a complex process, which involves cell migration, proliferation, angiogenesis and re-epithelialization. Several growth factors have been implicated in this process but the precise mechanism is not well understood. This study examined the involvement of VEGFR1 signaling in the gastric ulcer healing.

METHODS

Gastric ulcers were induced by the serosal application of 100% acetic acid, and the areas of the ulcers were measured thereafter.

RESULTS

The healing of acetic acid induced ulcers and the progenitor cells expressing CXCR4(+)VEGFR1(+) cell were significantly delayed in NSAID treated mice. The areas of the ulcer was significantly suppressed in tyrosine kinase-deficient VEGFR1 mice (VEGFR1TKKO) compared with wild type (WT) mice. The plasma level of SDF-1 and stem cell factor (SCF) and bone marrow level of pro-matrix metallopeptidase 9 (pro-MMP-9) were significantly reduced in VEGFR1TKKO mice. In VEGFR1 TKKOmice, the progenitor cells expressing CXCR4(+)VEGFR1(+) cell from bone marrow and the recruitment of these cells in healing ulcer were suppressed. Furthermore, VEGFR1 TKKO mice treated with NSAID did not suppress gastric ulcer healing compared to vehicle mice. These results suggested that NSAID suppressed VEGFR1 TK signaling plays a critical role in ulcer healing through mobilization of CXCR4(+)VEGFR1(+) cells.

CONCLUSION

VEGFR1 signaling is required for healing of NSAID induced gastric ulcer and angiogenesis with increased recruitment of CXCR4(+)VEGFR1(+) cells to the ulcerative lesion.

Prostaglandin receptor EP3 mediates growth inhibitory effect of aspirin through androgen receptor and contributes to castration resistance in prostate cancer cells

Although numerous epidemiological studies show aspirin to reduce risk of prostate cancer, the mechanism of this effect is unclear. Here, we first confirmed that aspirin downregulated androgen receptor (AR) and prostate-specific antigen in prostate cancer cells. We also found that aspirin upregulated prostaglandin receptor subtype EP3 but not EP2 or EP4. The EP3 antagonist L798106 and EP3 knockdown increased AR expression and cell proliferation, whereas the EP3 agonist sulprostone decreased them, indicating that EP3 affects AR expression. Additionally, EP3 (PTGER3) transcript levels were significantly decreased in human prostate cancer tissues compared with those in normal human prostate tissues, suggesting that EP3 is important to prostate carcinogenesis. Decreased EP3 expression was also seen in castration-resistant subtype CxR cells compared with parental LNCaP cells. Finally, we found that aspirin and EP3 modulators affected prostate cancer cell growth. Taken together, aspirin suppressed LNCaP cell proliferation via EP3 signaling activation; EP3 downregulation contributed to prostate carcinogenesis and to progression from androgen-dependent prostate cancer to castration-resistant prostate cancer by regulating AR expression. In conclusion, cyclooxygenases and EP3 may represent attractive therapeutic molecular targets in androgen-dependent prostate cancer.

Concurrent targeting of eicosanoid receptor 1/eicosanoid receptor 4 receptors and COX-2 induces synergistic apoptosis in Kaposi's sarcoma-associated herpesvirus and Epstein-Barr virus associated non-Hodgkin lymphoma cell lines

The effective antitumorigenic potential of nonsteroidal anti-inflammatory drugs (NSAIDs) and eicosonoid (EP; EP1-4) receptor antagonists prompted us to test their efficacy in Kaposi's sarcoma-associated herpesvirus (KSHV) and Epstein-Barr virus (EBV) related lymphomas. Our study demonstrated that (1) EP1-4 receptor protein levels vary among the various non-Hodgkin's lymphoma (NHL) cell lines tested (BCBL-1:KSHV+/EBV-;BC-3: KSHV+/EBV-; Akata/EBV+: KSHV-/EBV+; and JSC-1 cells: KSHV+/EBV + cells); (2) 5.0 μM of EP1 antagonist (SC-51322) had a significant antiproliferative effect on BCBL-1, BC-3, Akata/EBV+, and JSC-1 cells; (3) 50.0 μM of EP2 antagonist (AH6809) was required to induce a significant antiproliferative effect on BCBL-1, Akata/EBV+, and JSC-1 cells; (4) 5.0 μM of EP4 antagonist (GW 627368X) had a significant antiproliferative effect on BC-3, Akata/EBV+, and JSC-1 cells; (5) COX-2 selective inhibitor celecoxib (5.0 μM) had significant antiproliferative effects on BCBL-1, BC-3, Akata/EBV+, and JSC-1 cells; and (6) a combination of 1.0 μM each of celecoxib, SC-51322 and GW 627368X could potentiate the proapoptotic properties of celecoxib or vice-versa. Overall, our studies identified the synergistic antiproliferative effect of NSAIDs and EP receptor blockers on KSHV and EBV related B cell malignancies.

Non-steroid anti-inflammatory drugs, prostaglandins, and cancer

Fatty acids are involved in multiple pathways and play a pivotal role in health. Eicosanoids, derived from arachidonic acid, have received extensive attention in the field of cancer research. Following release from the phospholipid membrane, arachidonic acid can be metabolized into different classes of eicosanoids through cyclooxygenases, lipoxygenases, or p450 epoxygenase pathways. Non-steroid anti-inflammatory drugs (NSAIDs) are widely consumed as analgesics to relieve minor aches and pains, as antipyretics to reduce fever, and as anti-inflammatory medications. Most NSAIDs are nonselective inhibitors of cyclooxygenases, the rate limiting enzymes in the formation of prostaglandins. Long term use of some NSAIDs has been linked with reduced incidence and mortality in many cancers. In this review, we appraise the biological activities of prostanoids and their cognate receptors in the context of cancer biology. The existing literature supports that these lipid mediators are involved to a great extent in the occurrence and progression of cancer.

Role of prostaglandin receptor EP2 in the regulations of cancer cell proliferation, invasion, and inflammation

Population studies, preclinical, and clinical trials suggest a role for cyclooxygenase-2 (COX-2, PTGS2) in tumor formation and progression. The downstream prostanoid receptor signaling pathways involved in tumorigenesis are poorly understood, although prostaglandin E2 (PGE(2)), a major COX-2 metabolite which is usually upregulated in the involved tissues, presumably plays important roles in tumor biology. Taking advantage of our recently identified novel selective antagonist for the EP2 (PTGER2) subtype of PGE(2) receptor, we demonstrated that EP2 receptor activation could promote prostate cancer cell growth and invasion in vitro, accompanied by upregulation of the tumor-promoting inflammatory cytokines, such as IL-1β and IL-6. Our results suggest the involvement of prostaglandin receptor EP2 in cancer cell proliferation and invasion possibly via its inflammatory actions, and indicate that selective blockade of the PGE(2)-EP2 signaling pathway via small molecule antagonists might represent a novel therapy for tumorigenesis.

Anti- and Protumorigenic Effects of PPARγ in Lung Cancer Progression: A Double-Edged Sword

Peroxisome proliferator-activated receptor-γ (PPARγ) is a member of the nuclear receptor superfamily of ligand-activated transcription factors that plays an important role in the control of gene expression linked to a variety of physiological processes, including cancer. Ligands for PPARγ include naturally occurring fatty acids and the thiazolidinedione class of antidiabetic drugs. Activation of PPARγ in a variety of cancer cells leads to inhibition of growth, decreased invasiveness, reduced production of proinflammatory cytokines, and promotion of a more differentiated phenotype. However, systemic activation of PPARγ has been reported to be protumorigenic in some in vitro systems and in vivo models. Here, we review the available data that implicate PPARγ in lung carcinogenesis and highlight the challenges of targeting PPARγ in lung cancer treatments.

Role of COX-2 in lymphangiogenesis and restoration of lymphatic flow in secondary lymphedema

The pathophysiology of secondary lymphedema remains poorly understood. To clarify the roles of cyclooxygenase (COX)-2 in enhancement of lymphangiogenesis during secondary lymphedema, we tested a mouse tail model and evaluated the recurrence of lymph flow. To induce lymphedema, a circumferential incision was made in the tail of anesthetized mice to sever the dermal lymphatic vessels. The maximum diameters of the tails were measured weekly. We found that the diameters of the tails around the wounds were markedly increased after surgery, and reached maximum size 2 weeks after wounding in mice without a COX-2 inhibitor, celecoxib (Celecoxib-). Expression of COX-2 in wound granulation tissues was markedly increased 1 week after surgery compared with unwounded naive control mice. In Celecoxib-, recurrence of lymphatic flow in the wound granulation tissues was detected 3 weeks after surgical treatment. In contrast, lymphatic flow was markedly suppressed in mice treated with celecoxib (Celecoxib+). Newly formed lymphatic structures were identified in the granulation tissues formed at wounded lesions in Celecoxib-, whereas those were markedly suppressed in Celecoxib+. Interstitial tissue pressures in the distal areas of the tail wounds were markedly increased in Celecoxib+ with reduced expression of vascular endothelial cell growth factor (VEGF)-C. F4/80-positive cells were accumulated to the wound granulation tissues in Celecoxib-, and the accumulation of these cells was suppressed in Celecoxib+. Prostaglandin E(2) (PGE(2)) upregulated the expressions of VEGF-A and VEGF-C in cultured macrophages, but not human lymphatic microvascular endothelial cells. The present study therefore suggests that lymphangiogenesis, together with recurrence of lymph flow after surgical induction of lymphedema, is upregulated by COX-2 possibly via generation of PGs.

Microsomal prostaglandin E synthase-1 enhances bone cancer growth and bone cancer-related pain behaviors in mice

AIMS

Nonsteroidal anti-inflammatory drugs are a therapeutic modality for chronic cancer pain arising from bone metastases. Chronic administration of a cyclooxygenase (COX)-2 inhibitor is effective to bone cancer-related pain. However, adverse cardiovascular effects have limited COX-2 inhibitor therapy, and elucidation of better targets for blocking prostaglandin (PG) biosynthesis is necessary. Microsomal PGE synthase-1 (mPGES-1) is an inducible enzyme that catalyzes isomerization of the endoperoxide PGH(2) to PGE(2). To investigate the validity of mPGES-1 as a therapeutic target, we evaluated bone cancer pain-related behaviors in mPGES-1 knockout (PGES-1-/-) mice.

MAIN METHODS

Lewis lung carcinoma cells (LLCCs) were injected into the intramedullary space of the femur of wild-type (WT) and PGES-1-/- mice. Pain-related behaviors were evaluated.

KEY FINDINGS

PGES-1-/- mice exhibited reduced tumor growth in bone marrow compared to WT. The expression of pro-calcitonin gene-related peptide (CGPR) in the dorsal root ganglia of L(1-5) was significantly higher in WT mice at day 14, whereas it was unchanged in mPGES-1 mice. In the observation of pain-related behaviors, mPGES-1-/- mice exhibited significantly fewer spontaneous flinches and their onset was several days later than WT. The appearance of other pain-related behaviors in mPGES-1-/- mice was also delayed as compared to WT. LLCC-injected WT mice treated with a COX-2 inhibitor, celecoxib, exhibited similar temporal changes to mPGES1-/-.

SIGNIFICANCE

The present results suggest that mPGES-1 plays a crucial role in the enhancement of bone cancer growth and bone cancer pain, and that inhibition of mPGES-1 may have clinical utility in the management of bone cancer pain.

Roles of prostaglandin E2-EP3/EP4 receptor signaling in the enhancement of lymphangiogenesis during fibroblast growth factor-2-induced granulation formation

OBJECTIVE

One of the hallmarks of inflammation is lymphangiogesis that drains the interstitial fluids. During chronic inflammation, angiogenesis is induced by a variety of inflammatory mediators, such as prostaglandins (PGs). However, it remains unknown whether they enhance lymphangiogenesis. We examined the roles of cyclooxygenase-2 (COX-2) and PGE2 receptor signaling in enhancement of lymphangiogenesis during proliferative inflammation.

METHODS AND RESULTS

Lymphangiogenesis estimated by podoplanin/vascular endothelial growth factor (VEGF) receptor-3/LYVE-1 expression was upregulated during proliferative inflammation seen around and into subcutaneous Matrigel plugs containing fibroblast growth factor-2 (125 ng/site). A COX-2 inhibitor (celecoxib) significantly reduced lymphangiogenesis in a dose-dependent manner, whereas topical PGE2 enhanced lymphangiogenesis. Topical injection of fluorescein isothiocyanate-dextran into the Matrigel revealed that lymphatic flow from the Matrigels was COX-2 dependent. Lymphangiogenesis was suppressed in the granulation tissues of mice lacking either EP3 or EP4, suggesting that these molecules are receptors in response to endogenous PGE2. An EP3-selective agonist (ONO-AE-248) increased the expression of VEGF-C and VEGF-D in cultured macrophages, whereas an EP4-selective agonist (ONO-AE1-329) increased VEGF-C expression in cultured macrophages and increased VEGF-D expression in cultured fibroblasts.

CONCLUSIONS

Our findings suggest that COX-2 and EP3/EP4 signaling contributes to lymphangiogenesis in proliferative inflammation, possibly via induction of VEGF-C and VEGF-D, and may become a therapeutic target for controlling lymphangiogenesis.

Prostaglandin E₂ regulates cellular migration via induction of vascular endothelial growth factor receptor-1 in HCA-7 human colon cancer cells

An important event in the development of tumors is angiogenesis, or the formation of new blood vessels. Angiogenesis is also known to be involved in tumor cell metastasis and is dependent upon the activity of the vascular endothelial growth factor (VEGF) signaling pathway. Studies of mice in which the EP3 prostanoid receptors have been genetically deleted have shown a role for these receptors in cancer growth and angiogenesis. In the present study, human colon cancer HCA-7 cells were used as a model system to understand the potential role of EP3 receptors in tumor cell migration. We now show that stimulation of HCA-7 cells with PGE₂ enhanced the up-regulation of VEGF receptor-1 (VEGFR-1) expression by a mechanism involving EP3 receptor-mediated activation of phosphatidylinositol 3-kinase and the extracellular signal-regulated kinases. Moreover, the PGE₂ stimulated increase in VEGFR-1 expression was accompanied by an increase in the cellular migration of HCA-7 cells. Given the known involvement of VEGFR-1 in cellular migration, our results suggest that EP3 receptors may contribute to tumor cell metastasis by increasing cellular migration through the up-regulation of VEGFR-1 signaling.

Role of microsomal prostaglandin E synthase-1 in the facilitation of angiogenesis and the healing of gastric ulcers

The importance of prostaglandin E(2) in various pathophysiological events emphasizes the necessity of understanding the role of PGE synthases (PGESs) in vivo. However, there has been no report on the functional relevance of microsomal PGES-1 (mPGES-1) to the physiological healing processes of gastric ulcers, or to angiogenesis, which is indispensable to the healing processes. In this report, we tested whether mPGES-1 plays a role in the healing of gastric ulcers and in the enhancement of angiogenesis using mPGES-1 knockout mice (mPGES-1 KO mice) and their wild-type (WT) counterparts. Gastric ulcers were induced by the serosal application of 100% acetic acid, and the areas of the ulcers were measured thereafter. mPGES-1 together with cyclooxygenase-2 were induced in the granulation tissues compared with normal stomach tissues. The healing of acetic acid-induced ulcers was significantly delayed in mPGES-1 KO mice compared with WT. This was accompanied with reduced angiogenesis in ulcer granulation tissues, as estimated by CD31 mRNA levels determined by real-time PCR and the microvessel density in granulation tissues. The mRNA levels of proangiogenic growth factors, such as transforming growth factor-β, basic fibroblast growth factor, and connective tissue growth factor in ulcer granulation tissues determined were reduced in mPGES-1 KO mice compared with WT. The present results suggest that mPGES-1 enhances the ulcer-healing processes and the angiogenesis indispensable to ulcer healing, and that a selective mPGES-1 inhibitor should be used with care in patients with gastric ulcers.

Roles of prostaglandin E2-EP1 receptor signaling in regulation of gastric motor activity and emptying

It is widely accepted that the inhibition of gastric motor activity as well as the maintenance of gastric mucosal blood flow and mucous secretion are important for the homeostasis of the gastric mucosa. The present study was performed to ascertain whether or not endogenous PGs, which can protect the stomach from noxious stimuli, affect gastric motor activity and emptying. The myoelectrical activity of rat gastric smooth muscle was increased at intragastric pressures of over 2 cmH(2)O. Replacement of intragastric physiological saline with 1 M NaCl solution significantly increased PGI(2) and PGE(2) in stomach and suppressed the myoelectrical activity under a pressure of 2 cmH(2)O by 70%. Indomethacin inhibited the suppression of myoelectrical activity by 1 M NaCl. The myoelectrical activity under a pressure of 2 cmH(2)O was suppressed by continuous infusion of a selective EP1 agonist (ONO-DI-004, 3-100 nmol·kg(-1)·min(-1)) into the gastric artery in a dose-dependent manner, but not by that of the PGI receptor agonist beraprost sodium (100 nmol·kg(-1)·min(-1)). Suppression of myoelectrical activity with 1 M NaCl was inhibited by continuous infusion of a selective EP1 antagonist (ONO-8711, 100 nmol·kg(-1)·min(-1)) into the gastric artery. Furthermore, gastric emptying was tested in EP1 knockout mice and their wild-type counterparts. Gastric emptying was strongly suppressed with intragastric 1 M NaCl in wild-type mice, but this 1 M NaCl-induced suppression was not seen in EP1 knockout mice. These results suggest that PGE(2)-EP1 signaling has crucial roles in suppression of myoelectrical activity of gastric smooth muscles and inhibition of gastric emptying and that EP1 is an obvious target for drugs that control gastric emptying.

Piracy of prostaglandin E2/EP receptor-mediated signaling by Kaposi's sarcoma-associated herpes virus (HHV-8) for latency gene expression: strategy of a successful pathogen

Kaposi's sarcoma-associated herpes virus (KSHV) is implicated in the pathogenesis of KS, a chronic inflammation-associated malignancy. Cyclooxygenase-2 (COX-2) and its metabolite prostaglandin E2 (PGE2), two pivotal proinflammatory/oncogeneic molecules, are proposed to play roles in the expression of major KSHV latency-associated nuclear antigen-1 (LANA-1). Microsomal PGE2 synthase, PGE2, and its receptors (EP1, EP2, EP3, and EP4) were detected in KS lesions with the distinct staining of EP2/EP4 in KS lesions. In latently infected endothelial TIVE-LTC cells, EP receptor antagonists downregulated LANA-1 expression as well as Ca(2+), p-Src, p-PI3K, p-PKCzeta/lambda, and p-NF-kappaB, which are also some of the signal molecules proposed to be important in KS pathogenesis. Exogenous PGE2 and EP receptor agonists induced the LANA-1 promoter in 293 cells, and YY1, Sp1, Oct-1, Oct-6, C/EBP, and c-Jun transcription factors seem to be involved in this induction. PGE2/EP receptor-induced LANA-1 promoter activity was downregulated significantly by the inhibition of Ca(2+), p-Src, p-PI3K, p-PKCzeta/lambda, and p-NF-kappaB. These findings implicate the inflammatory PGE2/EP receptors and the associated signal molecules in herpes virus latency and uncover a novel paradigm that shows the evolution of KSHV genome plasticity to use inflammatory response for its survival advantage of maintaining latent gene expression. These data also suggest that potential use of anti-COX-2 and anti-EP receptor therapy may not only ameliorate the chronic inflammation associated with KS but could also lead to elimination of the KSHV latent infection and the associated KS lesions.

COX-2 and prostaglandin EP3/EP4 signaling regulate the tumor stromal proangiogenic microenvironment via CXCL12-CXCR4 chemokine systems

Bone marrow (BM)-derived hematopoietic cells, which are major components of tumor stroma, determine the tumor microenvironment and regulate tumor phenotypes. Cyclooxygenase (COX)-2 and endogenous prostaglandins are important determinants for tumor growth and tumor-associated angiogenesis; however, their contributions to stromal formation and angiogenesis remain unclear. In this study, we observed that Lewis lung carcinoma cells implanted in wild-type mice formed a tumor mass with extensive stromal formation that was markedly suppressed by COX-2 inhibition, which reduced the recruitment of BM cells. Notably, COX-2 inhibition attenuated CXCL12/CXCR4 expression as well as expression of several other chemokines. Indeed, in a Matrigel model, prostaglandin (PG) E2 enhanced stromal formation and CXCL12/CXCR4 expression. In addition, a COX-2 inhibitor suppressed stromal formation and reduced expression of CXCL12/CXCR4 and a fibroblast marker (S100A4) in a micropore chamber model. Moreover, stromal formation after tumor implantation was suppressed in EP3-/- mice and EP4-/- mice, in which stromal expression of CXCL12/CXCR4 and S100A4 was reduced. The EP3 or EP4 knockout suppressed S100A4+ fibroblasts, CXCL12+, and/or CXCR4+ stromal cells as well. Immunofluorescent analyses revealed that CXCL12+CXCR4+S100A4+ fibroblasts mainly comprised stromal cells and most of these were recruited from the BM. Additionally, either EP3- or EP4-specific agonists stimulated CXCL12 expression by fibroblasts in vitro. The present results address the novel activities of COX-2/PGE2-EP3/EP4 signaling that modulate tumor biology and show that CXCL12/CXCR4 axis may play a crucial role in tumor stromal formation and angiogenesis under the control of prostaglandins.

Host prostaglandin EP3 receptor signaling relevant to tumor-associated lymphangiogenesis

Prostaglandin E(2) (PGE(2)) and prostaglandin E (EP) receptor signaling pathways have been implicated in the promotion of tumor growth and angiogenesis. However, little is known about their roles in lymphangiogenesis during tumor development. The present study evaluates whether endogenous PGE(2) exhibits a critical role in tumor-associated lymphangiogenesis. Treatment of male C57BL/6 mice with a cyclooxygenase-2 inhibitor, celecoxib, for seven days resulted in a 52.4% reduction in tumor size induced by subcutaneous injection of murine Lewis lung cells. Celecoxib treatment down-regulated the expression of vascular endothelial growth factor receptor (VEGFR)-3 in stromal tissues by 73.9%, and attenuated expression of podoplanin, a marker for lymphatic endothelial cells. To examine the role of host PGE receptor signaling, we tested four kinds of EP receptor knockout mice. At Day 7 after tumor cell implantation, EP3 receptor knockout mice, but not EP receptor knockout mice lacking EP1, EP2, or EP4, exhibited a 53.3% reduction in tumor weight, which was associated with a 74.5% reduction in VEGFR-3 mRNA expression in tumor stromal tissues. At Day 14, VEGFR-3 expression in EP3-/- mice remained significantly lower than that of their wild-type (WT) counterparts. The expression of VEGF-C in the tumor stromal tissues in EP3-/- mice were also reduced by 22.1% (Day 7) and 44.1% (Day 14), respectively. In addition, the level of immunoreactive podoplanin in the tumor tissues from EP3-/- mice was less than that of WT. These results suggest that host EP3 receptor signaling regulates tumor-associated lymphangiogenesis by up-regulating expression of VEGF-C and its receptor, VEGFR-3, in tumor stromal tissues. Host EP3 blockade together with COX-2 inhibition may be a novel therapeutic strategy to suppress tumor-associated lymphangiogenesis.

Prostanoid receptor antagonists: development strategies and therapeutic applications

Identification of the primary products of cyclo-oxygenase (COX)/prostaglandin synthase(s), which occurred between 1958 and 1976, was followed by a classification system for prostanoid receptors (DP, EP(1), EP(2) ...) based mainly on the pharmacological actions of natural and synthetic agonists and a few antagonists. The design of potent selective antagonists was rapid for certain prostanoid receptors (EP(1), TP), slow for others (FP, IP) and has yet to be achieved in certain cases (EP(2)). While some antagonists are structurally related to the natural agonist, most recent compounds are 'non-prostanoid' (often acyl-sulphonamides) and have emerged from high-throughput screening of compound libraries, made possible by the development of (functional) assays involving single recombinant prostanoid receptors. Selective antagonists have been crucial to defining the roles of PGD(2) (acting on DP(1) and DP(2) receptors) and PGE(2) (on EP(1) and EP(4) receptors) in various inflammatory conditions; there are clear opportunities for therapeutic intervention. The vast endeavour on TP (thromboxane) antagonists is considered in relation to their limited pharmaceutical success in the cardiovascular area. Correspondingly, the clinical utility of IP (prostacyclin) antagonists is assessed in relation to the cloud hanging over the long-term safety of selective COX-2 inhibitors. Aspirin apart, COX inhibitors broadly suppress all prostanoid pathways, while high selectivity has been a major goal in receptor antagonist development; more targeted therapy may require an intermediate position with defined antagonist selectivity profiles. This review is intended to provide overviews of each antagonist class (including prostamide antagonists), covering major development strategies and current and potential clinical usage.

Regulator of G-protein signaling (RGS) proteins in cancer biology

The regulator of G-protein signaling (RGS) family is a diverse group of multifunctional proteins that regulate cellular signaling events downstream of G-protein coupled receptors (GPCRs). In recent years, GPCRs have been linked to the initiation and progression of multiple cancers; thus, regulators of GPCR signaling are also likely to be important to the pathophysiology of cancer. This review highlights recent studies detailing changes in RGS transcript expression during oncogenesis, single nucleotide polymorphisms in RGS proteins linked to lung and bladder cancers, and specific roles for RGS proteins in multiple cancer types.

Prostaglandin E2 receptors and COX enzymes in human hepatocellular carcinoma: role in the regulation of cell growth

The aim of this study was to investigate the expression of prostaglandin E(2) receptors (EP(1-4)), cyclooxygenase-1 (COX-1), and COX-2 in nontumor and tumor human liver tissues, and also to evaluate the antitumor activity of selective EP(1) receptor antagonist used alone or in combination with COX-1 and COX-2 selective inhibitors. Semiquantitative PCR analyses revealed that EP(1-4), COX-1, and COX-2 mRNA expression was detected in nearly all the tissue samples assayed, although with a high variability between nontumor and tumor tissues. In vitro EP(1) receptor antagonist inhibited anchorage-independent cell growth and reduced the viability of hepatocellular carcinoma (HCC) cells in a dose-dependent manner. Moreover, treatment with the combination of EP(1) receptor antagonist and COX inhibitors produced a significantly greater cell growth inhibition than the single agent alone. These findings suggest that the EP(1) receptor may represent an important target for HCC treatment, and in addition they could provide preclinical support for a combined chemotherapeutic approach with EP(1) antagonists and COX inhibitors in the treatment of liver cancer.

Bone marrow-derived EP3-expressing stromal cells enhance tumor-associated angiogenesis and tumor growth

Recent results suggest that bone marrow (BM)-derived hematopoietic cells are major components of tumor stroma and play crucial roles in tumor growth and angiogenesis. An E-type prostaglandin is known to regulate angiogenesis. We examined the role of BM-derived cells expressing an E-type prostaglandin receptor subtype (EP3) in tumor-induced angiogenesis and tumor growth. The replacement of wild-type (WT) BM with BM cells (BMCs) from green fluorescent protein (GFP) transgenic mice revealed that the stroma developed via the recruitment of BMCs. Selective knockdown of EP3 by recruitment of genetically modified BMCs lacking EP3 receptors was performed by transplantation of BMCs from EP3 knockout (EP3(-/-)) mice. Tumor growth and tumor-associated angiogenesis were suppressed in WT mice transplanted with BMCs from EP3(-/-) mice, but not in mice transplanted with BMCs from either EP1(-/-), EP2(-/-), or EP4(-/-) mice. Immunohistochemical analysis revealed that vascular endothelial growth factor (VEGF) expression was suppressed in the stroma of mice transplanted with BMCs from EP3(-/-) mice. EP3 signaling played a significant role in the recruitment of VEGFR-1- and VEGFR-2-positive cells from the BM to the stroma. These results indicate that the EP3 signaling expressed in bone marrow-derived cells has a crucial role in tumor-associated angiogenesis and tumor growth with upregulation of the expression of the host stromal VEGF together with the recruitment of VEGFR-1/VEGFR-2-positive. The present study suggests that the blockade of EP3 signaling and the recruitment of EP3-expressing stromal cells may become a novel strategy to treat solid tumors.

Cooperation of adenosine and prostaglandin E2 (PGE2) in amplification of cAMP-PKA signaling and immunosuppression

INTRODUCTION

We hypothesize that adenosine and PGE2 could have a complementary immunosuppressive effect that is mediated via common cAMP-PKA signaling.

MATERIALS AND METHODS

To test this hypothesis, the effect of adenosine and PGE2 on the cytotoxic activity and cytokine production of lymphokine activated killer (LAK) cells was investigated.

RESULTS

PGE2 and adenosine inhibited LAK cells cytotoxic activity and production of INF-gamma, GM-CSF and TNF-alpha. In combination they showed substantially higher inhibition than each modality used alone. Using agonists and antagonists specific for PGE2 and adenosine receptors we found that cooperation of PGE2 and adenosine in their inhibitory effects are mediated via EP2 and A2A receptors, respectively. LAK cells have 35-fold higher expression of EP2 than A2A. Combined PGE2 and adenosine treatment resulted in augmentation of cAMP production, PKA activity, CREB phosphorylation and inhibition of Akt phosphorylation. Wortmannin and LY294002 enhanced the suppressive effects of adenosine and PGE2. In contrast, Rp-8-Br-cAMPS, an inhibitor of PKA type I blocked their immunosuppressive effects, suggesting that the inhibitory effects of PGE2 and adenosine are mediated via common pathway with activation of cAMP-PKA and inhibition of Akt.

CONCLUSION

In comparison to other immunosuppressive molecules (TGF-beta and IL-10), adenosine and PGE2 are unique in their ability to inhibit the executive function of highly cytotoxic cells. High intratumor levels of adenosine and PGE2 could protect tumor from immune-mediated destruction by inactivation of the tumor infiltrating functionally active immune cells.

Tumor-growth-promoting cyclooxygenase-2 prostaglandin E2 pathway provides medulloblastoma therapeutic targets

Prostaglandin E(2) (PGE(2)) has been shown to play important roles in several aspects of tumor development and progression. PGE(2) is synthesized from arachidonic acid by cyclooxygenases (COX) and prostaglandin E synthases (PGES) and mediates its biological activity through binding to the four prostanoid receptors EP(1) through EP(4). In this study, we show for the first time that medulloblastoma (MB), the most common malignant childhood brain tumor, expresses high levels of COX-2, microsomal prostaglandin E synthase-1, and EP(1) through EP(4) and secretes PGE(2). PGE(2) and the EP(2) receptor agonist butaprost stimulated MB cell proliferation. Treatment of MB cells with COX inhibitors suppressed PGE(2) production and induced caspase-dependent apoptosis. Similarly, specific COX-2 silencing by small interfering RNA inhibited MB cell growth. EP(1) and EP(3) receptor antagonists ONO-8713 and ONO-AE3-240, but not the EP(4) antagonists ONO-AE3-208 and AH 23848, inhibited tumor cell proliferation, indicating the significance of EP(1) and EP(3) but not EP(4) for MB growth. Administration of COX inhibitors at clinically achievable nontoxic concentrations significantly inhibited growth of established human MB xenografts. Apoptosis was increased, proliferation was reduced, and angiogenesis was inhibited in MBs treated with COX inhibitors. This study suggests that PGE(2) is important for MB growth and that therapies targeting the prostanoid metabolic pathway are potentially beneficial and should be tested in clinical settings for treatment of children with MB.

PGE2 induces angiogenesis via MT1-MMP-mediated activation of the TGFbeta/Alk5 signaling pathway

The development of a new vascular network is essential for the onset and progression of many pathophysiologic processes. Cyclooxygenase-2 displays a proangiogenic activity in in vitro and in vivo models, mediated principally through its metabolite prostaglandin E(2) (PGE(2)). Here, we provide evidence for a novel signaling route through which PGE(2) activates the Alk5-Smad3 pathway in endothelial cells. PGE(2) induces Alk5-dependent Smad3 nuclear translocation and DNA binding, and the activation of this pathway involves the release of active TGFbeta from its latent form through a process mediated by the metalloproteinase MT1-MMP, whose membrane clustering is promoted by PGE(2). MT1-MMP-dependent transforming growth factor beta (TGFbeta) signaling through Alk5 is also required for PGE(2)-induced endothelial cord formation in vitro, and Alk5 kinase activity is required for PGE(2)-induced neovascularization in vivo. These findings identify a novel signaling pathway linking PGE(2) and TGFbeta, 2 effectors involved in tumor growth and angiogenesis, and reveal potential targets for the treatment of angiogenesis-related disorders.

Roles of calcitonin gene-related peptide in maintenance of gastric mucosal integrity and in enhancement of ulcer healing and angiogenesis

BACKGROUND & AIMS

The gastrointestinal tract is known to be rich in neural systems, among which afferent neurons are reported to exhibit protective actions. We tested whether an endogenous neuropeptide, calcitonin gene-related peptide (CGRP), can prevent gastric mucosal injury elicited by ethanol and enhance healing of acetic acid-induced ulcer using CGRP knockout mice (CGRP(-/-)).

METHODS

The stomach was perfused with 1.6 mmol/L capsaicin or 1 mol/L NaCl, and gastric mucosal injury elicited by 50% ethanol was estimated. Levels of CGRP in the perfusate were determined by enzyme immunoassay. Gastric ulcers were induced by serosal application of absolute acetic acid.

RESULTS

Capsaicin inhibited injured area dose-dependently. Fifty percent ethanol containing capsaicin immediately increased intragastric levels of CGRP in wild-type (WT) mice, although 50% ethanol alone did not. The protective action of capsaicin against ethanol was completely abolished in CGRP(-/-). Preperfusion with 1 mol/L NaCl increased CGRP release and reduced mucosal damage during ethanol perfusion. However, 1 mol/L NaCl was not effective in CGRP(-/-). Healing of ulcer elicited by acetic acid in CGRP(-/-) mice was markedly delayed, compared with that in WT. In WT, granulation tissues were formed at the base of ulcers, and substantial neovascularization was induced, whereas those were poor in CGRP(-/-). Expression of vascular endothelial growth factor was more markedly reduced in CGRP(-/-) than in WT.

CONCLUSIONS

CGRP has a preventive action on gastric mucosal injury and a proangiogenic activity to enhance ulcer healing. These results indicate that the CGRP-dependent pathway is a good target for regulating gastric mucosal protection and maintaining gastric mucosal integrity.

Gastric mucosal protection against ethanol by EP2 and EP4 signaling through the inhibition of leukotriene C4 production

Prostaglandin (PG)E derivatives are widely used for treating gastric mucosal injury. PGE receptors are classified into four subtypes, EP(1), EP(2), EP(3), and EP(4). We have tested which EP receptor subtypes participate in gastric mucosal protection against ethanol-induced gastric mucosal injury and clarified the mechanisms of such protection. The gastric mucosa of anesthetized rats was perfused at 2 ml/min with physiological saline, agonists for EP(1), EP(2), EP(3), and EP(4), or 50% ethanol, using a constant-rate pump connected to a cannula placed in the esophagus. The gastric microcirculation of the mucosal base of anesthetized rats was observed by transillumination through a window made by removal of the adventitia and muscularis externa. PGE(2) and subtype-specific EP agonists were applied to the muscularis mucosae at the window. Application of 50% ethanol dilated the mucosal arterioles and constricted the collecting venules. Collecting venule constriction by ethanol was completely inhibited by PGE(2) and by EP(2) and EP(4) agonists (100 nM) but not by an EP(1) or an EP(3) agonist. Ethanol-induced mucosal injury was also inhibited by EP(2) and EP(4) agonists. When leukotriene (LT)C(4) levels in the perfusate of the gastric mucosa were determined by ELISA, intragastric ethanol administration elevated the LTC(4) levels sixfold from the basal levels. These elevated levels were significantly (60%) reduced by both EP(2) and EP(4) agonists but not by other EP agonists. Since LTC(4) application at the window constricted collecting venules strongly, and an LTC antagonist reduced ethanol-induced mucosal injury, reductions in LTC(4) generation in response to EP(2) and EP(4) receptor signaling may be relevant to the protective action of PGE(2). The present results indicate that EP(2) and EP(4) receptor signaling inhibits ethanol-induced gastric mucosal injury through cancellation of collecting venule constriction by reducing LTC(4) production.

The expression pattern of prostaglandin E synthase and EP receptor isoforms in normal mouse skin and preinvasive skin neoplasms

Prostaglandin (PG) E(2), the predominant PG in skin, accumulates in experimentally produced mouse skin tumors. PGE(2) induces proliferation of mouse keratinocytes in vitro, epidermal hyperplasia and dysplasia, a promoted epidermis phenotype, and angiogenesis in keratin 5 promoter (K5) cyclooxygenase (COX)-2-transgenic NMRI mouse skin in vivo. PGE(2) is synthesized by COX-catalysed oxygenation of arachidonic acid to PGH(2) and its conversion to PGE(2) by prostaglandin E synthase (PGES) isoforms. PGE(2) signals via PGE(2) receptor isoforms EP1-EP4. Here, we investigated the expression profiles of PGES and EP receptors in wild type NMRI mouse skin constitutively expressing COX-1 when compared with the hyperplastic/dysplastic skin of homozygous K5 COX-2-transgenic mice and papillomas of both genotypes, which, in addition to COX-1, overexpress COX-2. The three PGES are constitutively expressed in normal and transgenic skin independent of the COX expression status. In papillomas, the increased PGE(2) levels correlate with an increased expression of mPGES-1 and cPGES. All four EP receptors were expressed in normal and transgenic skin. Only EP3 was slightly increased in transgenic skin. In papillomas of both genotypes, the expression levels of EP1 and EP4 were low when compared with those in wild type back skin. EP2 was the predominant receptor in papillomas of wild type and transgenic mice. In papillomas of wild type mice EP3 levels were slightly elevated when compared with transgenic tumors. EP1 and EP2 were localized in basal keratinocytes, sebaceous glands and CD31-positive vessels. Thus, normal and preinvasive mouse skin express the complete protein repertoire for PGE(2) biosynthesis and signalling.

Ochratoxin A: An overview on toxicity and carcinogenicity in animals and humans

Ochratoxin A (OTA) is a ubiquitous mycotoxin produced by fungi of improperly stored food products. OTA is nephrotoxic and is suspected of being the main etiological agent responsible for human Balkan endemic nephropathy (BEN) and associated urinary tract tumours. Striking similarities between OTA-induced porcine nephropathy in pigs and BEN in humans are observed. International Agency for Research on Cancer (IARC) has classified OTA as a possible human carcinogen (group 2B). Currently, the mode of carcinogenic action by OTA is unknown. OTA is genotoxic following oxidative metabolism. This activity is thought to play a central role in OTA-mediated carcinogenesis and may be divided into direct (covalent DNA adduction) and indirect (oxidative DNA damage) mechanisms of action. Evidence for a direct mode of genotoxicity has been derived from the sensitive 32P-postlabelling assay. OTA facilitates guanine-specific DNA adducts in vitro and in rat and pig kidney orally dosed, one adduct comigrates with a synthetic carbon (C)-bonded C8-dG OTA adduct standard. In this paper, our current understanding of OTA toxicity and carcinogenicity are reviewed. The available evidence suggests that OTA is a genotoxic carcinogen by induction of oxidative DNA lesions coupled with direct DNA adducts via quinone formation. This mechanism of action should be used to establish acceptable intake levels of OTA from human food sources.

EP2 prostanoid receptor promotes squamous cell carcinoma growth through epidermal growth factor receptor transactivation and iNOS and ERK1/2 pathways

In squamous cell carcinoma, the levels of nitric oxide (NO) derived from inducible NO synthase (iNOS) and prostaglandin E2 (PGE2) derived from cyclooxygenase-2 (COX-2) originated from tumor cells or tumor-associated inflammatory cells have been reported to correlate with tumor growth, metastasis, and angiogenesis. The present study examined the role of the iNOS signaling pathway in PGE2-mediated tumor invasiveness and proliferation in squamous cell carcinoma, A431, and SCC-9 cells. Cell invasion and proliferation promoted by PGE2 were blocked by iNOS silencing RNA or iNOS/guanylate cyclase (GC) pharmacological inhibition. Consistently, iNOS-GC pathway inhibitors blocked mitogen-activated protein kinase-ERK1/2 phosphorylation, which was required to mediate PGE2 functions. In vivo, in A431 cells implanted in nude mice, GC inhibition also decreased the tumor proliferation index and ERK1/2 activation. PGE2 effects were confined to the selective stimulation of the EP2 receptor subtype, leading to epidermal growth factor receptor (EGFR) transactivation via protein kinase A (PKA) and c-Src activation. EP2-mediated ERK1/2 activation and cell functions were abolished by inhibitors of PKA, c-Src, and EGFR, as well as by inhibiting iNOS pathway. Silencing of iNOS also impaired EGFR-induced ERK1/2 phosphorylation. These results indicate that iNOS/GC signaling is a downstream player in the control of EP2/EGFR-mediated tumor cell proliferation and invasion.

Genotoxic activity and induction of biotransformation enzymes in two human cell lines after treatment by Erika fuel extract

On 12 December 1999, the tanker Erika broke in two parts at about 60km from the Brittany French coasts (Point of Penmarc'h, Sud Finistère, France). About 10,000tonnes of heavy oil fuel were released in the sea. DNA adduct have been detected in fish liver and mussels digestive gland exposed to the Erika oil spill. In order to investigate the mechanism by which Erika fuel extract exhibits genotoxic effects the induction of DNA adducts by an Erika fuel extract have been analysed on two cell lines, human epithelial bronchial cells (WI) and human hepatoma cells. DNA adducts, reflected by a diagonal radioactive zone and individual adducts are detected only in hepatoma cells indicating biotransformation via CYP 1A2 and CYP 1B1. In addition, Erika fuel extract induces some metabolizing enzymes such CYP 1A2, COX2 and 5-LOX, the two later are involved in cancer processes. Formation of leucotrienes B4 (LTB(4)), a mediator playing a role in inflammation, is induced in epithelial bronchial cells. Since inhalation is one of the ways of contamination for human, the above results are important for human health and prevention.

Recruitment of a prostaglandin E receptor subtype, EP3-expressing bone marrow cells is crucial in wound-induced angiogenesis

E-type prostaglandins have been reported to be proangiogenic in vivo. Thus, we examined prostaglandin receptor signaling relevant to wound-induced angiogenesis. Full-thickness skin wounds were created on the backs of mice, and angiogenesis in wound granulation tissues was estimated. Wound closure and re-epithelization in EP3 receptor knockout mice (EP3-/-) were significantly delayed compared with their wild-type (WT) mice, whereas those in EP1-/-, EP2-/-, and EP4-/- were not delayed. Wound-induced angiogenesis estimated with CD31 immunohistochemistry in EP3-/- mice was significantly inhibited compared with that in WT mice. Immunoreactive vascular endothelial growth factor (VEGF) in wound granulation tissues in EP3-/- mice was markedly less than that in WT mice. Wound closure in WT mice was delayed significantly by VEGF neutralizing antibody compared with control IgG. Wound-induced angiogenesis and wound closure were significantly suppressed in EP3-/- bone marrow transplantation mice compared with those in WT bone marrow transplantation mice. These were accompanied with the reductions in accumulation of VEGF-expressing cells in wound granulation tissues and in mobilization of VEGF receptor 1-expressing leukocytes in peripheral circulation. These results indicate that the recruitment of EP3-expressing cells to wound granulation tissues is critical for surgical wound healing and angiogenesis via up-regulation of VEGF.

Celecoxib treatment alters the gene expression profile of normal colonic mucosa

A clinical trial was recently conducted to evaluate the safety and efficacy of a selective inhibitor of cyclooxygenase-2 (celecoxib) in hereditary nonpolyposis colon cancer patients. In a randomized, placebo-controlled phase I/II multicenter trial, hereditary nonpolyposis colon cancer patients and gene carriers received either celecoxib at one of two doses or placebo. The goal was to evaluate the effects of these treatment arms on a number of endoscopic and tissue-based biomarker end points after 12 months of treatment. As part of this trial, we analyzed gene expression by cDNA array technology in normal descending (rectal) colonic mucosa of patients before and after treatment with celecoxib or placebo. We found that treatment of patients with celecoxib at recommended clinical doses (200 and 400 mg p.o. bid), in contrast to treatment with placebo, leads to changes in expression of >1,400 genes in the healthy colon, although in general, the magnitude of changes is <2-fold. Twenty-three of 25 pairs of colon biopsies taken before and after celecoxib treatment can be classified correctly by the pattern of gene expression in a leave-one-out cross-validation. Immune response, particularly T- and B-lymphocyte activation and early steps of inflammatory reaction, cell signaling and cell adhesion, response to stress, transforming growth factor-beta signaling, and regulation of apoptosis, are the main biological processes targeted by celecoxib as shown by overrepresentation analysis of the distribution of celecoxib-affected genes across Gene Ontology categories. Analysis of possible cumulative effects of celecoxib-induced changes in gene expression indicates that in healthy colon, celecoxib may suppress the immune response and early steps of inflammation, inhibit formation of focal contacts, and stimulate transforming growth factor-beta signaling.

What are cyclooxygenases and lipoxygenases doing in the driver's seat of carcinogenesis?

Substantial evidence supports a functional role for cyclooxygenase- and lipoxygenase-catalyzed arachidonic and linoleic acid metabolism in cancer development. Genetic intervention studies firmly established cause-effect relations for cyclooxygenase-2, but cyclooxygenase-1 may also be involved. In addition, pharmacologic cyclooxygenase inhibition was found to suppress carcinogenesis in both experimental mouse models and several cancers in humans. Arachidonic acid-derived eicosanoid or linoleic acid-derived hydro[peroxy]fatty acid signaling are likely to be involved impacting fundamental biologic phenomena as diverse as cell growth, cell survival, angiogenesis, cell invasion, metastatic potential and immunomodulation. However, long chain unsaturated fatty acid oxidation reactions indicate antipodal functions of distinct lipoxygenase isoforms in carcinogenesis, i.e., the 5- and platelet-type 12-lipoxygenase exhibit procarcinogenic activities, while 15-lipoxygenase-1 and 15-lipoxygenase-2 may suppress carcinogenesis.

Deficient E-cadherin adhesion in C57BL/6J-Min/+ mice is associated with increased tyrosine kinase activity and RhoA-dependent actomyosin contractility

The Min/+ mouse is a model for APC-dependent colorectal cancer (CRC). We showed that tumorigenesis in this animal was associated with decreased E-cadherin adhesion and increased epidermal growth factor receptor (Egfr) activity in the non-tumor intestinal mucosa. Here, we tested whether these abnormalities correlated with changes in the actin cytoskeleton due to increased Rho-ROCK signaling. We treated Apc+/+ (WT) littermate small intestine with EGTA, an inhibitor of E-cadherin, and with LPA, an RhoA activator; both induced effects on adhesion and kinase activity that mimicked the Min/+ phenotype. GTP-bound Rho was increased in Min/+ enterocytes relative to WT. Since RhoA activity is associated with actomyosin contractility, markers of this signaling cascade were assessed including phosphorylated myosin light chain (MLC), cofilin, Pyk2, Src, and MAPK kinases. The increased actomyosin contractility characterizing Min/+ intestinal tissue was suppressed by the ROCK inhibitor, Y27632, but was inducible in the WT by EGTA or LPA. Finally, ultrastructural imaging revealed changes consistent with actomyosin contractility in Min/+ enterocytes. Thus, the positive regulation of E-cadherin adhesion provided by Apc+ in vivo allows proper negative regulation of Egfr, Src, Pyk2, and MAPK, as well as RhoA activities.