Retinoid antagonism of NF-IL6: insight into the mechanism of antiproliferative effects of retinoids in Kaposi's sarcoma

The Use of Retinoids for the Prevention and Treatment of Skin Cancers: An Updated Review

Retinoids are natural and synthetic vitamin A derivatives that are effective for the prevention and the treatment of non-melanoma skin cancers (NMSC). NMSCs constitute a heterogenous group of non-melanocyte-derived skin cancers that impose substantial burdens on patients and healthcare systems. They include entities such as basal cell carcinoma and cutaneous squamous cell carcinoma (collectively called keratinocyte carcinomas), cutaneous lymphomas and Kaposi’s sarcoma among others. The retinoid signaling pathway plays influential roles in skin physiology and pathology. These compounds regulate diverse biological processes within the skin, including proliferation, differentiation, angiogenesis and immune regulation. Collectively, retinoids can suppress skin carcinogenesis. Both topical and systemic retinoids have been investigated in clinical trials as NMSC prophylactics and treatments. Desirable efficacy and tolerability in clinical trials have prompted health regulatory bodies to approve the use of retinoids for NMSC management. Acceptable off-label uses of these compounds as drugs for skin cancers are also described. This review is a comprehensive outline on the biochemistry of retinoids, their activities in the skin, their effects on cancer cells and their adoption in clinical practice.

Involution of classic Kaposi sarcoma lesions under acitretin treatment Kaposi sarcoma treated with acitretin

Acitretin, indicated for generalized pustular psoriasis, was effective in concomitant classic Kaposi sarcoma.

Design, Synthesis, and Characterization of Globular Orphan Nuclear Receptor Regulator with Biological Activity in Soft Tissue Sarcoma

Sarcomas are rare and heterogeneous cancer variants of mesenchymal origin. Their genetic heterogeneity coupled with uncertain histogenesis makes them difficult to treat and results in poor prognosis. In this work, we show that structure-based drug discovery involving computational modeling can be used to identify a new retinoid X receptor (RXR) agonist ligand with a bis(indolyl)methane scaffold. This agent co-self-assembles with an amphiphilic diblock copolymer resulting in nanoparticles (Nano-RXR) with excellent kinetic stability, which were evaluated for efficacy and safety in transformed sarcoma cells, 63-3 Cre and 141-10 Cre of pig origin, and in rodent xenograft models. Responses at gene and protein levels established the treatment approach as a highly effective RXR agonist across cell, rodent, and "Oncopig" models. Interestingly, Nano-RXR was not only able to modulate metabolic and transporter genes related to orphan nuclear receptors but also played a major role in modulating programmed cell death in sarcomas developed in Oncopigs.

Role of nuclear receptors in breast cancer stem cells

The recapitulation of primary tumour heterogenity and the existence of a minor sub-population of cancer cells, capable of initiating tumour growth in xenografts on serial passages, led to the hypothesis that cancer stem cells (CSCs) exist. CSCs are present in many tumours, among which is breast cancer. Breast CSCs (BCSCs) are likely to sustain the growth of the primary tumour mass, as well as to be responsible for disease relapse and metastatic spreading. Consequently, BCSCs represent the most significant target for new drugs in breast cancer therapy. Both the hypoxic condition in BCSCs biology and pro-inflammatory cytokine network has gained increasing importance in the recent past. Breast stromal cells are crucial components of the tumours milieu and are a major source of inflammatory mediators. Recently, the anti-inflammatory role of some nuclear receptors ligands has emerged in several diseases, including breast cancer. Therefore, the use of nuclear receptors ligands may be a valid strategy to inhibit BCSCs viability and consequently breast cancer growth and disease relapse.

Retinoic acid regulates gap junction intercellular communication in human endometrial stromal cells through modulation of the phosphorylation status of connexin 43

Previous studies revealed that gap junction intercellular communication (GJIC) among uterine stromal cells plays critical roles in modulating decidualization, neovasularization, and embryo implantation. Connexin (Cx) proteins are the major component of gap junctions and Cx43 is the most widely expressed connexin in endometrium. Phosphorylation of Cx43 was found to impair gap junction communication in this tissue. Using primary human endometrial stromal cells (ESCs) and a stable high telomerase-expressing ESC transfectant (T-HESC), we found that retinoic acid (RA) altered the phosphorylation status of Cx43 protein such that there was a decrease in the phosphorylated (P1 and P2) species accompanied by an increase in the non-phosphorylated (P0) form. This process is dependent on protein phosphatase 2A (PP2A) activity since selective PP2A inhibitors prevented the ability of RA to dephosphorylate Cx43. Although RA had no effect on total PP2A expression or activity, it significantly increased the intracellular association of Cx43 and PP2A. Inhibition of transcription and protein synthesis by actinomycin D and cycloheximide, respectively, had no effect on the RA-induced changes in the Cx43 phosphorylation pattern. Furthermore, BMS493, a potent antagonist of the classical RA-mediated transcriptional pathway, did not inhibit RA-induced Cx43 dephosphorylation. Our data indicate that RA stimulates physical association of PP2A with Cx43, resulting in the dephosphorylation of Cx43 and, as a consequence, up-regulation of GJIC in ESCs. This process is independent of new mRNA and protein synthesis and suggests a novel mechanism by which aberrant retinoid metabolism can explain certain reproductive disorders manifested by dysfunctional endometrial cell GJIC.

Retinoid metabolism and its effects on the vasculature

Retinoids, the metabolically-active structural derivatives of vitamin A, are critical signaling molecules in many fundamental biological processes including cell survival, proliferation and differentiation. Emerging evidence, both clinical and molecular, implicates retinoids in atherosclerosis and other vasculoproliferative disorders such as restenosis. Although the data from clinical trials examining effect of vitamin A and vitamin precursors on cardiac events have been contradictory, this data does suggest that retinoids do influence fundamental processes relevant to atherosclerosis. Preclinical animal model and cellular studies support these concepts. Retinoids exhibit complex effects on proliferation, growth, differentiation and migration of vascular smooth muscle cells (VSMC), including responses to injury and atherosclerosis. Retinoids also appear to exert important inhibitory effects on thrombosis and inflammatory responses relevant to atherogenesis. Recent studies suggest retinoids may also be involved in vascular calcification and endothelial function, for example, by modulating nitric oxide pathways. In addition, established retinoid effects on lipid metabolism and adipogenesis may indirectly influence inflammation and atherosclerosis. Collectively, these observations underscore the scope and complexity of retinoid effects relevant to vascular disease. Additional studies are needed to elucidate how context and metabolite-specific retinoid effects affect atherosclerosis. This article is part of a Special Issue entitled: Retinoid and Lipid Metabolism.

The effect of synthetic retinoid, Am80, on T helper cell development and antibody production in murine collagen-induced arthritis

Retinoids are known to promote T helper (Th)2 and regulatory T cell (Treg) differentiation, and suppress Th1 and Th17 in vitro. Am80, a synthetic retinoid, is reported to ameliorate collagen-induced arthritis (CIA). The aims of this study are to determine the effects of Am80 on CIA in detail, and on Th development and antibody (Ab) production in vivo. Murine CIA was induced by immunization with bovine type II collagen (CII) at days 1 and 22. Treatment with Am80 from day 1 to 35 significantly lowered clinical arthritis score, suppressed cellular infiltration and bone destruction in the joint, decreased interleukin (IL)-17 and increased interferon (IFN)-gamma production by CII-stimulated splenocytes, and decreased proportion of Foxp3(+) splenic CD4 T cells and serum anti-CII Ab levels. Thus, Am80 inhibited Th17 and Treg and enhanced Th1 differentiation in vivo. In contrast, Am80 applied from day 15 to 35 did not alter arthritis score, IL-17 or IFN-gamma production by CII-stimulated splenocytes, but decreased the proportion of Foxp3(+) splenic CD4 T cells and serum anti-CII Ab levels. Am80 exhibits inhibitory effects on CIA and might regulate both Th development and Ab production in vivo. Decreased Th17 by treatment with Am80 might be responsible for the attenuation of arthritis.

KSHV-induced notch components render endothelial and mural cell characteristics and cell survival

Kaposi sarcoma-associated herpesvirus (KSHV) infection is essential to the development of Kaposi sarcoma (KS). Notch signaling is also known to play a pivotal role in KS cell survival and lytic phase entrance of KSHV. In the current study, we sought to determine whether KSHV regulates Notch components. KSHV-infected lymphatic endothelial cells showed induction of receptors Notch3 and Notch4, Notch ligands Dll4 and Jagged1, and activated Notch receptors in contrast to uninfected lymphatic endothelial cells. In addition, KSHV induced the expression of endothelial precursor cell marker (CD133) and mural cell markers (calponin, desmin, and smooth muscle alpha actin), suggesting dedifferentiation and trans-differentiation. Overexpression of latency proteins (LANA, vFLIP) and lytic phase proteins (RTA, vGPCR, viral interleukin-6) further supported the direct regulatory capacity of KSHV viral proteins to induce Notch receptors (Notch2, Notch3), ligands (Dll1, Dll4, Jagged1), downstream targets (Hey, Hes), and endothelial precursor CD133. Targeting Notch pathway with gamma-secretase inhibitor and a decoy protein in the form of soluble Dll4 inhibited growth of KSHV-transformed endothelial cell line. Soluble Dll4 was also highly active in vivo against KS tumor xenograft. It inhibited tumor cell growth, induced tumor cell death, and reduced vessel perfusion. Soluble Dll4 is thus a candidate for clinical investigation.

Retinoic acid modulates retinaldehyde dehydrogenase 1 gene expression through the induction of GADD153-C/EBPbeta interaction

Mammalian class I aldehyde dehydrogenase (ALDH) plays an important role in the biosynthesis of the hormone retinoic acid (RA), which modulates gene expression and cell differentiation. RA has been shown to mediate control of human ALDH1 gene expression through modulation of the retinoic acid receptor alpha (RARalpha) and the CCAAT/enhancer binding protein beta (C/EBPbeta). The positive activation of these transcription factors on the ALDH1 promoter is inhibited by RA through a decrease of C/EBPbeta binding to the ALDH1 CCAAT box response element. However, the mechanism of this effect remains unknown. Here we report that the RARalpha/retinoid X receptor beta (RXRbeta) complex binds to the mouse retinaldehyde dehydrogenase 1 (Raldh1) promoter at a non-consensus RA response element (RARE) with similar affinity to that of the consensus RARE. We found that C/EBPbeta binds to a Raldh1 CCAAT box located at -82/-58bp, adjacent to the RARE. Treatment with RA increases GADD153 and GADD153-C/EBPbeta interaction resulting in a decreased cellular availability of C/EBPbeta for binding to the Raldh1 CCAAT box. These data support a model in which high RA levels inhibit Raldh1 gene expression by sequestering C/EBPbeta through its interaction to GADD153.

All-trans retinoic acid suppresses interleukin-6 expression in interleukin-1-stimulated synovial fibroblasts by inhibition of ERK1/2 pathway independently of RAR activation

INTRODUCTION

Interleukin-6 (IL-6) is thought to play a pathogenic role in rheumatoid arthritis and synovium is a major source of IL-6 release. We investigated the ability of retinoids to suppress IL-6 expression in IL-1-stimulated synovial fibroblasts, with special care to the contribution of retinoic acid receptor (RAR) and retinoid X receptor (RXR) subtypes, and the implication of the mitogen-activated protein kinase (MAPK) pathway.

METHODS

RAR-alpha, -beta, and -gamma and RXR-alpha, -beta, and -gamma levels were determined by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) or Western blot in rat synovial fibroblasts stimulated with 10 ng/mL of IL-1beta. Stimulated levels of IL-6 were assessed by RT-qPCR or immunoassays in the presence or absence of 1 microM all-trans retinoic acid (ATRA) (RAR agonist) or 0.3 microM BMS-649 (RXR agonist). The contribution of RAR subtypes was checked with selective agonists or small interfering RNAs. The effect of ATRA on upstream MAPK (p38 MAPK, c-Jun N-terminal kinase [JNK], and extracellularly regulated kinase 1/2 [ERK1/2]) was assessed by Western blot, and the contribution of the ERK1/2 pathway to the activation of pro-inflammatory transcription factors was studied by TransAm assays.

RESULTS

Synovial fibroblasts expressed all RAR and RXR subtypes except RXR-gamma. In IL-1-stimulated cells, ATRA, but not BMS-649, reduced IL-6 expression whereas selective RAR agonists were inactive. The inhibitory effect of ATRA on IL-6 was not affected by the silencing of RAR subtypes. ATRA also reduced the phosphorylation of ERK1/2, but not of p38 MAPK or of JNK. The suppressive effect of ATRA on the activation of activator protein-1 (AP-1) and nuclear factor-IL-6 (NF-IL-6) was reproduced by the MEK1 (mitogen-activated protein extracellularly regulated kinase kinase 1) inhibitor PD-98059, whereas ATRA and PD-98059 had no effect on NF-kappaB activation.

CONCLUSIONS

Among RAR and RXR agonists, only ATRA inhibited IL-1-induced IL-6 expression in rat synovial fibroblasts by inhibiting ERK1/2 pathway and subsequent activation of AP-1 and NF-IL-6 independently of RAR.

Retinoic Acid Analogues Inhibit Human Herpesvirus 8 Replication

Background

Retinoids have a pronounced antiviral effect against several viruses. In this study we aimed to investigate the effect of retinoids on human herpesvirus 8 (HHV-8).

Methods

A panel of retinoic acid compounds were tested for their antiviral activity against HHV-8 in human umbilical vascular endothelial cells (HUVECs) and in a human epithelial cell line. The presence, transcription and antigen expression of HHV-8 in infected cells – in the presence or absence of retinoic acid compounds – were evaluated by PCR, reverse transcriptase PCR and immunofluorescence assays; HHV-8 viral load was determined by real-time quantitative PCR. Angiogenesis induced by HHV-8 was also assessed using Cultrex® basement membrane extract.

Results

The compounds tested specifically inhibited viral promoters, during the early and late phases of infection in both cell systems tested, and resulted in up to 100fold reduction of viral titre and release of progeny virus. The inhibition of viral replication induced by retinoids in endothelial cells, the primary target of HHV-8-driven transformation in Kaposi's Sarcoma, prevented endothelial cells from developing spindle morphology and in vitro tube formation, characteristic changes associated with HHV-8 infection and transformation.

Conclusions

We show that retinoids inhibit HHV-8 replication and identify new retinoid compounds with a strong antiviral effect. Selective retinoids, particularly those with retinoic acid receptor agonist activity, may be good candidates for the development of antiviral drugs.

Retinoid receptors

"Retinoid" refers to the naturally occurring compounds with vitamin A activity and to synthetic analogues of retinol. Retinoids are key regulators of differentiation, proliferation, and inflammation. Their successful use in the treatment of various skin diseases and neoplasias has revolutionized the practice of dermatology as well as oncology. This article focuses on the retinoid receptors to elucidate our understanding of their complex biologic activity that is reflected in their therapeutic clinical effects as well as in their adverse reactions.

[Retinoid therapy for autoimmune diseases]

Retinoid is a collective term for compounds which bind to and activate retinoic acid receptors (RARalpha, beta, gamma and RXRalpha, beta, gamma), members of nuclear hormone receptor superfamily. The most important endogeneous retinoid is all-trans-retinoic acid (ATRA) which is an RARalpha, beta and gamma ligand. ATRA and its mimics have been in clinical use for treatment of acute promyelocytic leukemia (APL) and some skin diseases. Many synthetic retinoids have been developed and attempts to improve their medicinal properties have been made. Among them, tamibarotene (Am80) is an RARalpha- and RARbeta-specific (but RARgamma- and RXRs-nonbinding) synthetic retinoid that is effective in the treatment of psoriasis patients and relapsed APL. Experimentally, this compound is also active in animal models of rheumatoid arthritis and experimental autoimmune encephalomyelitis. On this background, possible application of retinoids for the treatment of autoimmune diseases was discussed. In particular, Th1 dominant autoimmune diseases may be the targets of the retinoids.

Synthetic retinoid Am80 reduces scavenger receptor expression and atherosclerosis in mice by inhibiting IL-6

BACKGROUND

Macrophage scavenger receptors facilitate the uptake of modified low-density lipoprotein (LDL), formation of foam cells, and development of atherosclerosis. Given that proinflammatory cytokines, including IL-6, can modulate the macrophage foaming process, the aim of the present study was to determine whether the synthetic retinoic acid receptor-alpha/beta-specific agonist Am80, which is also an IL-6 inhibitor, can modulate macrophage lipid accumulation and foam cell formation.

METHODS AND RESULTS

Am80 suppressed IL-6 production induced by 12-myristate 13-acetate (PMA) or angiotensin II in mouse Raw264 macrophages. It also suppressed expression of the 2 major scavenger receptors (scavenger receptor-A [SR-A] and CD36), in part by inhibiting IL-6, and inhibited macrophage foam cell formation. Systemic administration of Am80 led to reductions in the areas of atherosclerotic lesions and foam cell accumulation in the aortas of apolipoprotein E (apoE)-deficient mice and reduced serum concentrations of IL-6 and IL-1beta without affecting body weights, serum lipid profiles or IL-10 levels.

CONCLUSIONS

Am80 suppresses scavenger receptor expression and macrophage foam cell formation in vitro and prevents atherogenesis in apoE-deficient mice in vivo. This suggests Am80 is a novel candidate agent that could be highly useful in the prevention and treatment of atherosclerosis.

Therapeutic options for human herpesvirus-8/Kaposi's sarcoma-associated herpesvirus-related disorders

Human herpesvirus-8/Kaposi's sarcoma-associated herpesvirus infection is associated with three proliferative disorders in immunocompromised patients - Kaposi's sarcoma, primary effusion lymphoma and multicentric Castleman's disease. These disorders often develop in patients with advanced AIDS who present a number of therapeutic challenges, underscoring the importance of continuing efforts dedicated to basic and clinical research in this field. In the era of highly active antiretroviral therapy, the incidence of AIDS and Kaposi's sarcoma has considerably decreased, presumably due to enhanced anti-Kaposi's sarcoma-associated herpesvirus immune responses, whereas the situation with primary effusion lymphoma and multicentric Castleman's disease is more complex. Based on advances in the understanding of Kaposi's sarcoma-associated herpesvirus-related disorders and availability of antiretroviral agents, current and future therapeutic approaches will be discussed.

Acne: Topical treatment

Acne vulgaris is a common skin disease, affecting about 70-80% of adolescents and young adults. It is a multifactorial disease of the pilosebaceous unit.(1) The influence of androgens at the onset of adolescence leads to an enlargement of the sebaceous gland and a rise in sebum production. Additional increased proliferation and altered differentiation of the follicular epithelium eventually blocks the pilosebaceous duct, leading to development of the microcomedo as the primary acne lesion. Concomitantly and subsequently, colonization with Propionibacterium acnes increases, followed by induction of inflammatory reactions from bacteria, ductal corneocytes, and sebaceous proinflammatory agents (Fig 1).(2-5)

Gene–nutrient interactions: importance of folates and retinoids during early embryogenesis

The role that nutritional factors play in mammalian development has received renewed attention over the past two decades, as the scientific literature exploded with reports of retinoid compounds disrupting craniofacial development, and with other reports that folic acid supplementation in the periconceptional period can protect embryos from highly significant malformations. As was often the case, the situation became far more complicated, as the interaction between nutritional factors with selected genes was recognized. In this review, we attempt to summarize a complex clinical and experimental literature of nutritional factors, their biological transport mechanisms, and the impact that they have during early embryogenesis. Although not exhaustive, our goal was to provide an overview of important gene-nutrient interactions and a framework for their investigation.

Clinical presentations and standard therapy of AIDS-associated Kaposi's sarcoma

The treatment plan for a patient with AIDS-related KS should be based on tumor characteristics, control of HIV infection, comorbidities, and patient treatment goals (see Table 1). Institution of optimal antiretroviral therapy is an essential component of KS therapy. When available, enrollment in a clinical trial should be considered, except for patients who are naive to chemotherapy with symptomatic or life-threatening KS. For a patient with minimal, indolent cutaneous disease, after optimal control of HIV replication, local treatment, investigational treatment, or interferon are reasonable considerations. For the patient with rapidly progressive, cutaneous disease, tumor-related symptoms, or visceral disease, cytotoxic chemotherapy in combination with antiretroviral therapy is the first consideration. Future advances undoubtedly will include pathogenesis-based agents, either alone or in combination with currently available cytotoxic therapy.

Inhibition of growth and sensitization to cisplatin-mediated killing of ovarian cancer cells by polyphenolic chemopreventive agents

The polyphenolic compounds curcumin and quercetin increased sensitivity of ovarian cancer cells (CAOV3 and SKOV3) to cisplatin. The effect was obtained when the compounds were added simultaneously with cisplatin, as well as when they were added 24 h before. High serum levels of certain cytokines, for example interleukin-6 (IL-6), have been associated with poor prognosis and cisplatin resistance in various forms of cancer. Furthermore, it has been hypothesized that cytokines may increase proliferation, metastasis, and stimulate production of detoxification enzymes and multi-drug resistant proteins. Curcumin inhibits the production of many cytokines. The two ovarian cell lines differ significantly in IL-6 production, and correspondingly the high producer, CAOV3, was less susceptible to cisplatin. Curcumin inhibited the production of IL-6 in this cell suggesting that one of the mechanisms for synergy between cisplatin and curcumin was by reducing the autologous production of IL-6. However, the synergy was also observed in the low IL-6 producer, SKOV3, indicating that the action was most probably a result of multiple targeting. In sum, this study suggests that the compounds, curcumin and quercetin, potentially may be useful for enhancing drug sensitivity in certain cancer.

A multicenter phase II study of the intravenous administration of liposomal tretinoin in patients with acquired immunodeficiency syndrome-associated Kaposi's sarcoma

BACKGROUND

A multicenter trial was conducted to determine the efficacy and toxicity of escalating dosages of liposomal tretinoin (all-trans-retinoic acid) administered once or three times weekly in patients with acquired immunodeficiency syndrome (AIDS)-associated Kaposi sarcoma.

METHODS

Seventy-six patients with acquired immunodeficiency syndrome (AIDS)-associated Kaposi sarcoma were randomized to receive the study drug either once (n = 30) or 3 times weekly (n = 46). The starting dosage was 60 mg/m(2), which was escalated to 90 mg/m(2) and then 120 mg/m(2) if the drug was well tolerated (<or= Grade 2 toxicities [according to the Southwest Oncology Group toxicity scale]). Four weeks of therapy constituted 1 cycle; patients could receive up to 8 cycles and those who completed 8 cycles were given the option of receiving extended therapy. Clinical response was defined as complete response (CR), partial response (PR), or stable disease (SD).

RESULTS

Efficacy was assessed after the completion of 3 treatment cycles; 28.9% of patients (22 of 76 patients) responded (no CRs, 1 PR, and 21 SDs). Among the patients receiving treatment 3 times weekly, 16 of 49 patients (32.7%) achieved a clinical response at the end of the third treatment cycle (no CRs, 1 PR, and 15 SDs). Concomitant or prior use of protease inhibitors did not appear to affect the patient's response to treatment (P = 0.183).

CONCLUSIONS

Liposomal tretinoin is a new therapeutic agent that has been reported to have some clinical activity in patients with AIDS-associated Kaposi sarcoma. A three-times-per-week dosing schedule was noted to be more effective compared with a once-a-week schedule without any significant difference in toxicity reported.

Treatment of Kaposi's sarcoma--an update

Kaposi's sarcoma (KS) is an angioproliferative disease of multifactorial origin arising in different clinic-epidemiologic forms, which show the same histopathological features. It generally starts as a hyperplastic reactive-inflammatory and angiogenic process, which may evolve into monomorphic nodules of KS cells that can be clonal (late-stage lesions) and resemble a true sarcoma. Infection with the human herpesvirus 8, cytokine- and angiogenic factor-induced growth together with an immuno-dysregulated state represent fundamental conditions for the development of this tumor. Several local therapies are used to eradicate early and confined skin lesions, whereas widely disseminated, progressive or symptomatic disease requires a more aggressive treatment. Although different chemotherapeutic agents have been used to treat aggressive KS, the growing understanding of the pathogenetic factors participating in KS development has provided a strong rationale for using less- or non-cytotoxic agents that block the mechanisms involved in KS pathogenesis. The angiogenic nature of KS makes it particularly suitable for using therapies based on anti-angiogenic agents. Of note on this goal, recent studies indicate that the highly active anti-retroviral therapy, including at least one human immunodeficiency virus (HIV) protease inhibitor (PI), is associated with a dramatic decrease in the incidence of AIDS-KS and with a regression of KS in treated individuals. Consistent with this, results from preclinical studies indicate that PIs have potent and direct anti-angiogenic and anti-KS activities, suggesting that they should be further investigated, alone or combined with other therapies, as a novel treatment for KS in both HIV seropositive or seronegative individuals.

Virology, pathogenetic mechanisms, and associated diseases of Kaposi sarcoma-associated herpesvirus (human herpesvirus 8)

Kaposi sarcoma-associated herpesvirus (KSHV) is a recently discovered and characterized member of the herpesvirus family. It is one of a few viruses proved to be associated with tumorigenesis in humans. Its causal association with 4 clinical and epidemiologic variants of Kaposi sarcoma (classic, endemic, iatrogenic, and acquired immunodeficiency virus-associated) as well as with several lymphoproliferative disorders (notably primary effusion lymphoma and multicentric Castleman disease) is reviewed critically. Issues related to the epidemiology, transmission, and molecular and serologic diagnosis are discussed. Several intriguing oncogenic mechanisms of KSHV infection have been identified. These are often dependent on the interaction of KSHV with other viruses, such as human immunodeficiency virus, Epstein-Barr virus, or both. However, important problems remain and once resolved will substantially enhance our understanding of oncogenesis in general and viral-induced oncogenesis in particular. This may also translate into improved treatment and perhaps prevention of this common and intriguing viral infection.

Molecular basis of environmentally induced birth defects

Exposure of the developing conceptus to selected environmental agents can lead to deleterious and often times lethal birth defects. These malformations result in serious emotional and financial consequences to families and societies worldwide. As we continue to progress technologically, we face challenges from the introduction of new pharmacological agents and chemical compounds into the environment. This results in a concomitant need to more fully understand the relationship between in utero exposure to environmental teratogens and the risk of congenital malformations. The goal of this review is to provide a current perspective of the major concepts related to the molecular basis of environmentally induced birth defects. Starting with a discussion of commonly occurring birth defects, we consider important fundamental facets of embryonic development, teratology, and gene-environment interactions. The review then summarizes our current understanding of the molecular mechanisms involved in selected birth defects following exposure to pharmacological compounds, including thalidomide, retinoids, and valproic acid. Understanding these signaling pathways may lead to the development of safer pharmaceutical compounds and a reduction in the number of infants born with preventable birth defects.

Retinoids induce the PAI-1 gene expression through tyrosine kinase-dependent pathways in vascular smooth muscle cells

Retinoids exert their pleiotropic effects on several pathophysiologic processes, including neointima formation after experimental vascular injury. Plasminogen activator inhibitor-1 (PAI-1) has been proposed to play an inhibitory role in arterial neointima formation after injury. We examined whether retinoids regulate PAI-1 expression in cultured vascular smooth muscle cells (SMCs). Northern blot analysis showed that all-trans retinoic acid (atRA) and 9-cis retinoic acid (9cRA) increased PAI-1 mRNA levels in a dose-dependent manner. These responses were completely inhibited by tyrosine kinase inhibitors. The half-life of PAI-1 was not affected by atRA, suggesting that induction of PAI-1 mRNA was mainly regulated at the transcriptional levels. Stable and transient transfection assays of the human PAI-1 promoter-luciferase constructs indicate that DNA sequence responsive to either ligand-stimulated or overexpressed retinoic acid receptor-alpha expression vector lies downstream of -363 relative to the transcription start site, where no putative retinoic acid response element is found. These results indicate that atRA and 9cRA increase PAI-1 gene transcription through pathways involving tyrosine kinases in SMCs. Because PAI-1 inhibits the production of fibrinolytic protein plasmin that facilitates SMC migration, induction of the PAI-1 gene expression by atRA may at least partly account for the role of atRA as an important inhibitor of neointima formation.

Antitumor activity of oral 9-cis-retinoic acid in HIV-associated Kaposi's sarcoma

OBJECTIVE

To assess the efficacy, safety and tolerance of oral 9-cis-retinoic acid in HIV-infected patients with Kaposi's sarcoma.

METHODS

Sixty-six patients with AIDS-related Kaposi's sarcoma were enrolled at 14 centers; 60 received the study medication and were analyzed and, of these, 45 (75%) had received prior therapy for Kaposi's sarcoma. Once daily oral 9-cis-retinoic acid (alitretinoin, Panretin) was administered at doses up to 140 mg/m2. Most patients (72%) received a maximum dose of 100 mg/m2. Response was assessed using AIDS Clinical Trials Group (ACTG) criteria.

RESULTS

The median age was 38 years and the median absolute CD4 cell count was 194 x 10(6) cells/l (range 6-784 x 10(6)). Despite the use of three- and four-drug antiviral regimens (83%), the median HIV RNA at baseline was 8701 copies/ml [range < 500 (lower limit of detection) to 4.24 x 10(6)]. The tumor response rate was 37% (95% confidence interval 25-49). Tumor response was associated with improved quality-of-life measures. There was a significant increase in interleukin 6 (IL-6) levels from baseline to week 4. Responders had significantly lower baseline soluble IL-6 receptor levels (P = 0.029) than non-responders. The median time to response was 9 weeks (mean, 13 weeks; range, 4-36). HIV RNA levels did not change significantly during therapy nor did they correlate with tumor responses. Study drug was discontinued by 28 patients for adverse events, which included headache (13) and skin toxicity (10).

CONCLUSION

Oral 9-cis-retinoic acid is an active antitumor drug for AIDS-related Kaposi's sarcoma. Treatment is associated with skin and constitutional toxicity and further studies are needed to improve its long-term tolerance.

[Castleman's disease in patients infected with HIV]

PURPOSE

Castleman's disease is a polyclonal lymphoplasmacytic and vascular proliferation prominant in lymphoid tissues. It is associated with lymph node enlargement, hepatosplenomegaly and fever. This manifestations could be secondary to hyperproduction of interleukin 6. The prognosis is poor. The opportunistic infections which are characteristic of severe HIV infection worsen the prognosis. Prolonged monochemotherapy with vinblastine or etoposide can control Castleman's disease.

CURRENT KNOWLEDGE AND KEY POINTS

Recent advances in human herpesvirus 8 (HHV8) knowledge and its predominance in the forms which are linked to the HIV seropositivity have partly explained the clinical manifestations of Castleman's disease. Indeed, HHV8 produce an homologous interleukin 6, the vIL-6, responsible for lymphoplasmacytic proliferation. The presence of other homologues of human cytokines produced by HHV8 could contribute to lymphoplasmacytosis and to endothelial proliferation.

FUTURE AND PROSPECTS

Taking into account this viral origin, alpha interferon could be an alternative in forms which are less progressive. However, antiviral therapy against HHV8 or HIV and the immunitary restoration do not have any influence on the evolution of Castleman's disease, contrary to opportunistic infections.

Developments in topical retinoid therapy for acne

Topical retinoic acid was introduced for acne treatment three decades ago. Since that time, researchers have discovered thousands of retinoids, originally defined as chemical analogs of vitamin A. After the identification of nuclear retinoid receptors in 1987, the definition of this class expanded to include molecules that bind to and activate such receptors. The receptor-selective retinoid agents, adapalene and tazarotene, were developed in the 1990s. Other innovations of the past decade include retinoid formulations and methods aimed at limiting retinoid absorption. Cutaneous irritation may be reduced without losing retinoid efficacy by inhibiting retinoid penetration into the deep epidermis and dermis. Examples include tretinoin in slow-release vehicles and the short-contact method of tazarotene gel therapy. Only trace amounts of adapalene are absorbed after topical application, perhaps explaining its relatively low irritancy. New formulations of existing agents, such as additional concentrations of tretinoin in microsphere gel and cream formulations of tazarotene, are now under investigation for acne. Current research focused on receptor selectivity holds the promise of yielding new retinoid molecules with improved benefits and safety.

Clinical aspects and management of AIDS-related Kaposi's sarcoma

AIDS-related Kaposi's sarcoma (KS) is a tumour of vascular endothelium, which is seen predominantly in men who have sex with men. The majority of affected individuals have advanced immunosuppression at the time of the initial KS diagnosis. The disease may present with cutaneous lesions, or with involvement of visceral organs, of which the gastrointestinal tract is most common. KS may also present with lymphoadenopathy or with isolated lymphoedema, even in the absence of cutaneous lesions. Affected individuals are uniformly co-infected with HIV and with Human Herpesvirus type 8 (HHV8). HHV8 is present within KS tissues, and is aetiological in the pathogenesis of disease, along with aberrant cytokine expression, production of multiple angiogenic peptides, and immune dysregulation. While not presently curable, multiple treatment options exist and must be evaluated in terms of the specific needs of the individual patient. Various local therapies are aimed at eradicating small lesions, while acknowledging that the KS in general, or its likelihood of recurring will be unaffected. Systemic chemotherapy is used to treat extensive visceral involvement. Knowledge of the pathogenesis of disease has led to the development of novel treatment strategies, aimed at HHV8 as the target of therapy, or at the inflammatory cytokine or angiogenic milieu necessary for KS growth. Use of highly active anti-retroviral therapy, aimed at controlling the underlying HIV infection, has been associated with a dramatic decrease in the incidence of KS, and may also be useful in the treatment of existing KS disease.

Kaposi sarcoma is a therapeutic target for vitamin D3receptor agonist

Kaposi sarcoma (KS) is responsive to a number of different steroid hormones, such as glucocorticoids and retinoids. An active metabolite of vitamin D, 1α,25 dihydroxyvitamin D3, was used to study the effect of this steroid hormone in KS. Steroid hormones exert their effect through their cognate nuclear receptors, which for vitamin D metabolites is the vitamin D receptor (VDR). It was first shown that KS cell lines and primary tumor tissue express high levels of VDR, whereas endothelial cells had minimal expression and fibroblasts had no expression. Second, KS cell growth was inhibited by VDR agonist 1α,25 dihydroxyvitamin D3 with a 50% inhibitory concentration of 5 × 10 −8 mol/L, whereas endothelial cells and fibroblast cells showed no response. Studies on the mechanism of KS tumor growth inhibition by 1α,25 dihydroxyvitamin D3 showed that production of autocrine growth factors interleukin (IL)-6 and IL-8 was reduced in a dose-dependent manner, whereas no effect was observed on vascular endothelial growth factor and basic fibroblast growth factor. Transcription initiated at the IL-6 promoter was repressed by VDR agonist. The DNA sequences required to mediate this repression were localized to nucleotides −225/−110 in the 5′-flanking region. The antitumor activity of VDR agonists was also confirmed in KS tumor xenograft and after topical application in patients with KS. 1α,25 Dihydroxyvitamin D3 and its analogs may thus be candidates for clinical development in KS.

Kaposi sarcoma is a therapeutic target for vitamin D3receptor agonist

Kaposi sarcoma (KS) is responsive to a number of different steroid hormones, such as glucocorticoids and retinoids. An active metabolite of vitamin D, 1α,25 dihydroxyvitamin D3, was used to study the effect of this steroid hormone in KS. Steroid hormones exert their effect through their cognate nuclear receptors, which for vitamin D metabolites is the vitamin D receptor (VDR). It was first shown that KS cell lines and primary tumor tissue express high levels of VDR, whereas endothelial cells had minimal expression and fibroblasts had no expression. Second, KS cell growth was inhibited by VDR agonist 1α,25 dihydroxyvitamin D3 with a 50% inhibitory concentration of 5 × 10 −8 mol/L, whereas endothelial cells and fibroblast cells showed no response. Studies on the mechanism of KS tumor growth inhibition by 1α,25 dihydroxyvitamin D3 showed that production of autocrine growth factors interleukin (IL)-6 and IL-8 was reduced in a dose-dependent manner, whereas no effect was observed on vascular endothelial growth factor and basic fibroblast growth factor. Transcription initiated at the IL-6 promoter was repressed by VDR agonist. The DNA sequences required to mediate this repression were localized to nucleotides −225/−110 in the 5′-flanking region. The antitumor activity of VDR agonists was also confirmed in KS tumor xenograft and after topical application in patients with KS. 1α,25 Dihydroxyvitamin D3 and its analogs may thus be candidates for clinical development in KS.

Mechanisms mediating the inhibitory effect of all-trans retinoic acid on primitive hematopoietic stem cells in human long-term bone marrow culture

All-trans retinoic acid (RA) has generally been found to stimulate late committed (colony-forming unit- granulocyte, macrophage [CFU-GM]) and inhibit early (CFU-Blast) normal human myeloid progenitor cells. The present study provides the first evidence that the pharmacological concentration of 1 microM RA, exerts an inhibitory effect on the proliferation of functional human primitive hemopoietic stem cells (cobblestone area-forming cell [CFAC]) in long-term bone marrow cultures. Treatment of four-week confluent bone marrow culture with 1 microM RA for five days significantly reduced week 4 CAFC from 88 +/- 10 in control cultures to only 52 +/- 12 per 10(5) cells, p < 0.01. Quantitative enzyme-linked immunosorbent assay measurement of interleukin 6 (IL-6) and IL-11 produced from the four-week bone marrow stroma culture revealed only a slight and moderate increase of IL-6 and IL-11 production after treatment with RA. On the other hand, treatment with RA profoundly increased the soluble receptor gp130 released from the four-week bone marrow stroma by 7.5-fold from only 145 +/- 2.1 pg per ml in control cultures to 1,069.9 +/- 3.8 pg per ml in RA-treated cultures. A similar marked increase in the soluble adhesion molecules ICAM-1, and to a lesser extent VCAM-1, released from the four-week bone marrow stroma was observed after RA treatment. IL-6 has been implicated in the inhibitory effect of RA in several human hemopoietic and nonhemopoietic cells. The common transducing signal chain gp130, for all receptors of the IL-6 cytokine family, is expressed in most primitive human hemopoietic CD34(+) cells and its signaling was shown to synergize with other hemopoietic cytokines to expand primitive human hemopoietic stem cells. Recently, soluble gp130 was shown to be a natural potent antagonist of the human IL-6 cytokine family by binding the ligand and thereby reducing its bioavailability. The profound and rapid 7.5-fold increase in the natural antagonist of human IL-6 cytokine family after RA treatment could abrogate the gp130 signaling required for proliferation and/or expansion of human primitive hemopoietic stem cells and lead to the observed inhibitory effect of RA on CAFC. Both adhesion molecules VCAM-1 and ICAM-1 mediate human hemopoietic stem cell adhesion to marrow stroma. The present significant increase in the soluble form of these adhesion molecules after RA treatment could exert a significant antagonist effect on their function and hence may impair CAFC adhesion to marrow stroma. In conclusion, the RA inhibitory effect on the proliferation of primitive human hemopoietic stem cells could be mediated through: A) an impaired hemopoietic stem cell adhesion due to the significant increase in soluble adhesion molecules released from the marrow stroma after RA treatment, and B) a significantly reduced gp130 signaling that is necessary for stem cell proliferation due to the natural antagonistic effect of the profoundly increased level of soluble gp130 released from the marrow stroma after treatment with RA.

Retinoic acid suppresses interleukin-6 production in human endometrial cells

OBJECTIVE

To determine whether retinoic acid (RA) can regulate the expression of interleukin (IL)-6 in human endometrial cells in a manner that might be beneficial to women with endometriosis.

DESIGN

In vitro study.

SETTING

Academic medical center.

PATIENT(S)

Patients with endometriosis and controls.

INTERVENTION(S)

Endometrial cell cultures were treated with RA.

MAIN OUTCOME MEASURE(S)

Interleukin-6 protein secretion, messenger RNA expression, and IL-6-promoter activity.

RESULT(S)

Using a human endometrial cell line (EM42), as well as primary stromal and epithelial endometrial cells, we demonstrated that RA suppresses IL-6 protein and messenger RNA expression in a time- and dose-dependent fashion, showing maximal effects at pharmacologically achievable blood serum concentrations (micromoles per liter). Retinoic acid specifically inhibited the activity of IL-6-promoter reporter constructs that were transiently transfected into EM42 cells. Mutational analysis of reporter constructs indicated that RA suppression of IL-6 expression was mediated, at least in part, through the nuclear factor IL-6 binding site located in the IL-6 promoter.

CONCLUSION

Retinoids may play a fundamental role in altering the pathophysiology of endometriosis related to aberrant production of IL-6.

Retinoic acid suppresses interleukin 6 production in normal human osteoblasts

Systemic long-term retinoid therapy for chronic skin diseases significantly reduced bone turnover markers within days and led to bone abnormalities. Retinoic acid (RA) plays a key role in the regulation of mouse bone cell proliferation, differentiation and functions. Meanwhile, there is little information of RA effect on human osteoblast and osteoclast cell development and function. Interleukin 6 (IL-6) is a pleiotropic cytokine with profound effects on bone metabolism. Thus, the present study examined the RA effect on cell differentiation, alkaline phosphatase and osteocalcin production as well as IL-6 production in normal human osteoblasts. The number of large differentiated osteoblast cells decreased in RA-treated cultures P<0.05. The production of bone specific markers, alkaline phosphatase and osteocalcin, was also reduced in RA-treated cultures. Normal human osteoblasts produced 31.0+/-4.8 pg IL-6 per ml in control cultures. Within 24 h, RA at all four concentrations reduced Il-6 production from normal human osteoblasts. The pharmacological concentration of 10(-5) M RA suppressed 90% of IL-6 production. The present study shows for the first time that RA profoundly inhibits IL-6 production in normal human osteoblasts within 24 h and in a dose-dependent manner. RA was shown previously to inhibit IL-6 production in several other normal and malignant human cell types. The associated decrease in osteoblast cell differentiation, alkaline phosphatase and osteocalcin production could result from the rapid RA-inhibition of IL-6 production. Thus, RA inhibition of IL-6 production in normal human osteoblasts may contribute to the bone abnormalities seen after systemic long-term retinoid therapy in some patients.

RAR gamma agonists inhibit proliferation of vascular smooth muscle cells

The multifactorial and unpredictable nature of human restenosis will probably necessitate interventional strategies that target multiple processes involved in neointimal proliferation. Retinoids represent a growing class of pleiotropic biologic response modifiers with demonstrable efficacy in managing several pathologic conditions pertaining to neointimal proliferation. However, retinoid treatment is associated with a high incidence of adverse effects. The action of all-trans-retinoic acid is mediated by two families of nuclear receptors, RARs and RXRs, each containing three isoforms alpha, beta, and gamma. Because synthetic retinoids that are receptor and function specific have been shown to differ from each other by several orders of magnitude in their potencies and are associated with limited adverse effects, we examined the effect of synthetic retinoids on serum- and serotonin-induced vascular smooth muscle cell (VSMC) proliferation. Naturally occurring retinoids were used as controls. All-trans-retinoic acid at nanomolar concentrations inhibited smooth muscle cell proliferation. In this study, we report that RAR gamma subgroup-specific agonists are the most potent inhibitors of serum and serotonin VSMC proliferation, as compared with other RAR pan-agonists and naturally occurring retinoids tested. Our results indicate that RAR gamma subgroup-specific agonists should be assessed further in in vivo models of neointimal proliferation.

Kaposi's sarcoma. New treatment modalities

Over the last 20 years of experience with the AIDS epidemic, we have accumulated a great body of knowledge on Kaposi's sarcoma (KS), a major cause of morbidity and mortality in AIDS patients, especially among homosexual and bisexual men. New antiretroviral therapies, in particular the protease inhibitors, appear to be changing the clinical course of KS. Now, it is not unusual to observe a complete resolution and control of KS with the use of these new agents. As we have begun to unravel the pathogenesis of KS, new treatment modalities have merged targeting some of its pathogenic pathways. Although, chemotherapy remains the cornerstone of its treatment, in particular with the new liposomal preparations, new agents may soon change our approach to KS. Experimental therapies being evaluated in ongoing clinical trials include angiogenesis inhibitors, hormonal therapies, retinoic acid derivatives, and immune modulators such as interleukin 12. Better treatment for HIV, and new experimental therapies targeting the pathogenic mechanisms of KS allow us to envision the future treatment of KS with a certain degree of optimism.

Treatment of AIDS-related cutaneous Kaposi's sarcoma with topical alitretinoin (9-cis-retinoic acid) gel. Panretin Gel North American Study Group

BACKGROUND

Kaposi's sarcoma (KS) is the most frequent malignancy in patients with HIV. Given the promise that retinoids show in the treatment of various hyperproliferative skin disorders and in vitro evidence of inhibition of proliferation of KS cells, a randomized, controlled clinical trial was conducted.

METHODS AND RESULTS

A 12-week, multicenter, randomized, double-blind, vehicle-controlled safety and efficacy evaluation of topical alitretinoin 0.1% gel applied to cutaneous KS lesions was conducted in HIV-infected patients. The primary efficacy endpoint was the patient's response rate, as determined by evaluating six index lesions representative of the patient's overall KS cutaneous disease using AIDS Clinical Trials Group (ACTG) response criteria applied to topical therapy. Of 268 patients entered in the blinded treatment phase of the study (alitretinoin group, n = 134; vehicle group, n = 134), 47 patients (35%) treated with alitretinoin 0.1% gel had a positive response, compared with 24 patients (18%) treated with vehicle gel. Of 184 patients receiving open-label alitretinoin treatment following the blinded phase of the trial, 90 patients (49%) met criteria for a positive response. This superior efficacy of alitretinoin gel over vehicle gel was maintained when the data were adjusted or analyzed for age, race, Kamofsky scores, baseline CD4+ lymphocyte counts, number of raised lesions at baseline, and aggregate area of index lesions. Alitretinoin 0.1% gel was superior to vehicle gel regardless of the number of concurrent antiretroviral therapies. Most adverse events were mild to moderate in severity, limited to the application site, and reversible on reduction in frequency or suspension of application. Relatively few patients (7%) discontinued alitretinoin therapy because of to related adverse events.

CONCLUSIONS

The results show that alitretinoin gel application is safe and generally well tolerated, and they indicate the superiority of alitretinoin 0.1% gel over vehicle gel in the treatment of cutaneous AIDS-related KS lesions.

Retinoic acid for treatment of multicentric Castleman's disease

Multicentric Castleman's syndrome has an aggressive course with poor prognosis, and its treatment remains uncertain. We report a woman with multicentric Castleman's disease that was successfully treated with prednisone and retinoic acid.

Hematopoietic differentiation activity of a recombinant human interleukin-6 (IL-6) isoform resulting from alternatively spliced deletion of the second exon

We have previously identified and cloned an alternatively spliced form of human interleukin-6 mRNA lacking exon II, which encodes amino acid residues known to be important in gp130-mediated signal transduction pathways. We expressed and purified the recombinant protein (rIL6-alt) resulting from this alternatively spliced mRNA and now report the initial characterization of its biologic activities with comparison to full length IL6 (rIL6-full). rIL6-alt was found to have 10(4) to 10(5) fold less activity in proliferation assays with 7TD1 murine plasmacytoma cells and did not competitively inhibit the stimulatory activity of rIL6-full. In addition, like rIL6-full, rIL6-alt had antiproliferative activity toward M1 murine myeloblast cells and was 10-200-fold less active than rIL6-full. In contrast, in assays with human HL60 promyelocytic leukemia cells, rIL6-alt had greater antiproliferative activity than rIL6-full and more strongly upregulated phagocytosis as well as surface expression of the differentiation antigen CD11b. rIL6-full and rIL6-alt upregulated the level of lysozyme mRNA in HL60 cells approximately equally. These findings suggest that IL6-alt, which lacks amino acid residues encoded by the second exon of the gene, is not a natural inhibitor of IL6-full but may be relatively tissue specific and may play a role in modulation of hematopoietic cell growth and differentiation.

Angiogenesis and Hematopoiesis Induced by Kaposi’s Sarcoma-Associated Herpesvirus-Encoded Interleukin-6

Kaposi’s sarcoma-associated herpesvirus (KSHV; also known as human herpesvirus 8 [HHV-8]) is a herpesvirus linked to the development of Kaposi’s sarcoma (KS), primary effusion lymphoma, and a proportion of Castleman’s disease. KSHV encodes viral interleukin-6 (vIL-6), which is structurally homologous to human and murine IL-6. The biological activities of vIL-6 are largely unknown. To gain insight into the biology of vIL-6, we expressed vIL-6 in murine fibroblasts NIH3T3 cells and inoculated stable vIL-6–producing clones into athymic mice. vIL-6 was detected selectively in the blood of mice injected with vIL-6–expressing clones. Compared with controls, vIL-6–positive mice displayed increased hematopoiesis in the myeloid, erythroid, and megakaryocytic lineages; plasmacytosis in spleen and lymph nodes; hepatosplenomegaly; and polyclonal hypergammaglobulinemia. vIL-6–expressing NIH3T3 cells gave rise to tumors more rapidly than did control cells, and vIL-6–positive tumors were more vascularized than controls. Vascular endothelial growth factor (VEGF) was detected at higher levels in the culture supernatant of vIL-6–expressing cells compared with controls, and immunohistochemical staining detected VEGF in spleen, lymph nodes, and tumor tissues from mice bearing vIL-6–producing tumors but not control tumors. Thus, vIL-6 is a multifunctional cytokine that promotes hematopoiesis, plasmacytosis, and angiogenesis. Through these functions, vIL-6 may play an important role in the pathogenesis of certain KSHV-associated disorders.

Physical Interaction Between Retinoic Acid Receptor and Sp1: Mechanism for Induction of Urokinase by Retinoic Acid

Induction of urokinase plasminogen activator (uPA) by retinoic acid (RA) is the initial event preceding certain subsequent biological changes in vascular endothelial cells. We investigated the molecular mechanism by which RA stimulates the expression of uPA, which lacks a canonical RA receptor (RAR)-responsive element, in bovine and human aortic endothelial cells. Upon stimulation with RA, mRNA levels of RAR and β transiently increased in parallel with the induction of uPA, and this increase was inhibited by cycloheximide. Results of transient transfection of RAR/RXR cDNAs and experiments using specific agonists and antagonists suggested that uPA induction is dependent upon RAR (initially, RAR) with the help of RXR. Deletion analysis of the uPA promoter suggested that RAR/RXR acts on GC box region within the uPA promoter. This was further supported by inhibition of Sp1 binding to this region. Coimmunoprecipitation studies, glutathioneS-transferase pull-down experiment, and mammalian two-hybrid assays suggested a physical interaction between RAR/RXR and Sp1. Furthermore, gel shift studies showed that the binding of Sp1 to the uPA GC box is significantly potentiated in the presence of RARs/RXRs. Finally, Sp1 and RAR/RXR synergistically enhanced the transactivation activity of the uPA promoter. These results suggest that (1) RA induces RARs mainly via RAR and that (2) RAR/RXR physically and functionally interact with Sp1, resulting in a potentiation of uPA transcription.

Angiogenesis and Hematopoiesis Induced by Kaposi’s Sarcoma-Associated Herpesvirus-Encoded Interleukin-6

Kaposi’s sarcoma-associated herpesvirus (KSHV; also known as human herpesvirus 8 [HHV-8]) is a herpesvirus linked to the development of Kaposi’s sarcoma (KS), primary effusion lymphoma, and a proportion of Castleman’s disease. KSHV encodes viral interleukin-6 (vIL-6), which is structurally homologous to human and murine IL-6. The biological activities of vIL-6 are largely unknown. To gain insight into the biology of vIL-6, we expressed vIL-6 in murine fibroblasts NIH3T3 cells and inoculated stable vIL-6–producing clones into athymic mice. vIL-6 was detected selectively in the blood of mice injected with vIL-6–expressing clones. Compared with controls, vIL-6–positive mice displayed increased hematopoiesis in the myeloid, erythroid, and megakaryocytic lineages; plasmacytosis in spleen and lymph nodes; hepatosplenomegaly; and polyclonal hypergammaglobulinemia. vIL-6–expressing NIH3T3 cells gave rise to tumors more rapidly than did control cells, and vIL-6–positive tumors were more vascularized than controls. Vascular endothelial growth factor (VEGF) was detected at higher levels in the culture supernatant of vIL-6–expressing cells compared with controls, and immunohistochemical staining detected VEGF in spleen, lymph nodes, and tumor tissues from mice bearing vIL-6–producing tumors but not control tumors. Thus, vIL-6 is a multifunctional cytokine that promotes hematopoiesis, plasmacytosis, and angiogenesis. Through these functions, vIL-6 may play an important role in the pathogenesis of certain KSHV-associated disorders.

Physical Interaction Between Retinoic Acid Receptor and Sp1: Mechanism for Induction of Urokinase by Retinoic Acid

Induction of urokinase plasminogen activator (uPA) by retinoic acid (RA) is the initial event preceding certain subsequent biological changes in vascular endothelial cells. We investigated the molecular mechanism by which RA stimulates the expression of uPA, which lacks a canonical RA receptor (RAR)-responsive element, in bovine and human aortic endothelial cells. Upon stimulation with RA, mRNA levels of RAR and β transiently increased in parallel with the induction of uPA, and this increase was inhibited by cycloheximide. Results of transient transfection of RAR/RXR cDNAs and experiments using specific agonists and antagonists suggested that uPA induction is dependent upon RAR (initially, RAR) with the help of RXR. Deletion analysis of the uPA promoter suggested that RAR/RXR acts on GC box region within the uPA promoter. This was further supported by inhibition of Sp1 binding to this region. Coimmunoprecipitation studies, glutathioneS-transferase pull-down experiment, and mammalian two-hybrid assays suggested a physical interaction between RAR/RXR and Sp1. Furthermore, gel shift studies showed that the binding of Sp1 to the uPA GC box is significantly potentiated in the presence of RARs/RXRs. Finally, Sp1 and RAR/RXR synergistically enhanced the transactivation activity of the uPA promoter. These results suggest that (1) RA induces RARs mainly via RAR and that (2) RAR/RXR physically and functionally interact with Sp1, resulting in a potentiation of uPA transcription.

Teratology of retinoids

Either an excess or a deficiency of vitamin A and related compounds (retinoids) causes abnormal morphological development (teratogenesis). Potential retinoid sources come from dietary intake, nutritional supplements, and some therapeutic drugs. Therefore, understanding the mechanisms of retinoid teratogenesis is important. This review first gives an overview of the principles of teratology as they apply to retinoid-induced malformations. It then describes relevant aspects of the biochemical pathway and signal transduction of retinoids. The teratogenic activity of various retinoid compounds, the role of the retinoid receptors, and important toxicokinetic parameters in teratogenesis are reviewed.