Separation of transactivation and AP1 antagonism functions of retinoic acid receptor alpha

Chemopreventive and Biological Strategies in the Management of Oral Potentially Malignant and Malignant Disorders

Oral potentially malignant disorders (OPMD) and oral squamous cell carcinoma (OSCC) represent a significant global health burden due to their potential for malignant transformation and the challenges associated with their diagnosis and treatment. Chemoprevention, an innovative approach aimed at halting or reversing the neoplastic process before full malignancy, has emerged as a promising avenue for mitigating the impact of OPMD and OSCC. The pivotal role of chemopreventive strategies is underscored by the need for effective interventions that go beyond traditional therapies. In this regard, chemopreventive agents offer a unique opportunity to intercept disease progression by targeting the molecular pathways implicated in carcinogenesis. Natural compounds, such as curcumin, green tea polyphenols, and resveratrol, exhibit anti-inflammatory, antioxidant, and anti-cancer properties that could make them potential candidates for curtailing the transformation of OPMD to OSCC. Moreover, targeted therapies directed at specific molecular alterations hold promise in disrupting the signaling cascades driving OSCC growth. Immunomodulatory agents, like immune checkpoint inhibitors, are gaining attention for their potential to harness the body's immune response against early malignancies, thus impeding OSCC advancement. Additionally, nutritional interventions and topical formulations of chemopreventive agents offer localized strategies for preventing carcinogenesis in the oral cavity. The challenge lies in optimizing these strategies for efficacy, safety, and patient compliance. This review presents an up to date on the dynamic interplay between molecular insights, clinical interventions, and the broader goal of reducing the burden of oral malignancies. As research progresses, the synergy between early diagnosis, non-invasive biomarker identification, and chemopreventive therapy is poised to reshape the landscape of OPMD and OSCC management, offering a glimpse of a future where these diseases are no longer insurmountable challenges but rather preventable and manageable conditions.

UVB-mediated DNA damage induces matrix metalloproteinases to promote photoaging in an AhR- and SP1-dependent manner

It is currently thought that UVB radiation drives photoaging of the skin primarily by generating ROS. In this model, ROS purportedly activates activator protein-1 to upregulate MMPs 1, 3, and 9, which then degrade collagen and other extracellular matrix components to produce wrinkles. However, these MMPs are expressed at relatively low levels and correlate poorly with wrinkles, suggesting that another mechanism distinct from ROS and MMP1/3/9 may be more directly associated with photoaging. Here we show that MMP2, which degrades type IV collagen, is abundantly expressed in human skin, increases with age in sun-exposed skin, and correlates robustly with aryl hydrocarbon receptor (AhR), a transcription factor directly activated by UV-generated photometabolites. Through mechanistic studies with HaCaT human immortalized keratinocytes, we found that AhR, specificity protein 1 (SP1), and other pathways associated with DNA damage are required for the induction of both MMP2 and MMP11 (another MMP implicated in photoaging), but not MMP1/3. Last, we found that topical treatment with AhR antagonists vitamin B₁₂ and folic acid ameliorated UVB-induced wrinkle formation in mice while dampening MMP2 expression in the skin. These results directly implicate DNA damage in photoaging and reveal AhR as a potential target for preventing wrinkles.

Fixed-Combination Halobetasol Propionate and Tazarotene in the Treatment of Psoriasis: Narrative Review of Mechanisms of Action and Therapeutic Benefits

Psoriasis is a lifelong disease associated with cycles of remission and relapse. Topical treatments are the front line of psoriasis therapy for most patients and have antiproliferative, anti-inflammatory, and immunosuppressive mechanisms of action. Novel fixed-dose combinations of topical therapeutic agents are becoming increasingly available, leveraging multiple mechanisms of action to improve safety and efficacy with formulations that are easier to use and may allow for the use of lower doses of active ingredients. A fixed-combination lotion containing the potent-to-superpotent corticosteroid halobetasol propionate (HP) and the retinoid tazarotene (HP 0.01%/TAZ 0.045%) was recently developed using polymeric emulsion technology. This new formulation technology allows for more uniform and efficient delivery of the active ingredients at lower doses than conventional monotherapy formulations of either ingredient while providing enhanced hydration and moisturization. This review provides an up-to-date overview of the therapeutic mechanisms of action of HP and TAZ, the rationale behind the development of HP 0.01%/TAZ 0.045% lotion, and clinical trials data on the efficacy, safety and tolerability, and maintenance of therapeutic effect with HP 0.01%/TAZ 0.045% lotion in the treatment of moderate-to-severe plaque psoriasis.

The role of the retinoid receptor, RAR/RXR heterodimer, in liver physiology

Activated by retinoids, metabolites of vitamin A, the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs) play important roles in a wide variety of biological processes, including embryo development, homeostasis, cell proliferation, differentiation and death. In this review, we summarized the functional roles of nuclear receptor RAR/RXR heterodimers in liver physiology. Specifically, RAR/RXR modulate the synthesis and metabolism of lipids and bile acids in hepatocytes, regulate cholesterol transport in macrophages, and repress fibrogenesis in hepatic stellate cells. We have also listed the specific genes that carry these functions and how RAR/RXR regulate their expression in liver cells, providing a mechanistic view of their roles in liver physiology. Meanwhile, we pointed out many questions regarding the detailed signaling of RAR/RXR in regulating the expression of liver genes, and hope future studies will address these issues.

Retinoic acid receptor γ is a therapeutically targetable driver of growth and survival in prostate cancer

BACKGROUND

Prostate cancer (PC) tissue contains all-trans retinoic acid (ATRA) at a very low level (10-9 M), at least an order of magnitude lower than in adjacent normal healthy prostate cells or benign prostate hyperplasia. When this is coupled with deregulated expression of the intracellular lipid-binding proteins FABP5 and CRABP2 that is frequently found in PC, this is likely to result in the preferential delivery of ATRA to oncogenic PPARβ/δ rather than retinoic acid receptors (RARs). There are three isotypes of RARs (RARα, RARβ, and RARγ) and recent studies have revealed discrete physiological roles. For example, RARα and RARγ promote differentiation and self-renewal, respectively, which are critical for proper hematopoiesis.

AIMS

We have previously shown that ATRA stimulates transactivation of RARγ at sub-nanomolar concentrations (EC50 0.24 nM), whereas an 80-fold higher concentration was required for RARα-mediated transactivation (EC50 19.3 nM). Additionally, we have shown that RAR pan-antagonists inhibit the growth of PC cells (at 16-34 nM). These findings, together with the low level of ATRA in PC, led us to hypothesize that RARγ plays a role in PC pathogenesis and that RARγ-selective antagonism may be an effective treatment.

METHODS AND RESULTS

We found that concentrations of 10-9 M and below of ATRA promoted survival/proliferation and opposed adipogenic differentiation of human PC cell lines by a mechanism that involves RARγ. We also found that a RARγ-selective antagonist (AGN205728) potently induced mitochondria-dependent, but caspase-independent, cell death in PC cell lines. Furthermore, AGN205728 demonstrated synergism in killing PC cells in combination with cytotoxic chemotherapeutic agents.

CONCLUSION

We suggest that the use of RARγ-selective antagonists may be effective in PC (and potentially other cancers), either as a single agent or in combination with cytotoxic chemotherapy.

Pharmacokinetics of tazarotene and acitretin in psoriasis

INTRODUCTION

Psoriasis is a prevalent cutaneous condition with severe physical and psychological manifestations. Since the advent of biologics, clinical outcomes in psoriasis have improved. However, retinoids are useful in the correct clinical context. Tazarotene and acitretin are currently the only US Food and Drug Administration approved retinoids for treatment of psoriasis. Both topical tazarotene and oral acitretin act on retinoic acid receptors and retinoid-X-receptors, resulting in altered gene expression of inflammatory cytokines and inhibition of keratinocyte proliferation. Areas covered: This article provides an in-depth pharmacologic and clinical review on the use of tazarotene and acitretin in psoriasis. The PubMed database was searched using combinations of keywords: acitretin, bioavailability, dosing, efficacy, etretinate, interactions, mechanism, pharmacodynamics, pharmacokinetics, pharmacogenetics, psoriasis, safety, tazarotene, tolerability, and toxicity. Expert opinion: Tazarotene and acitretin are effective treatments for psoriasis. Benefits include lack of immunosuppression and success treating inflammatory psoriasis. When combined with other topical and systemic agents, both retinoids improve clinical efficacy while lowering the treatment threshold. However, topical adherence and bothersome side effects can limit retinoid use. Acitretin and tazarotene both improve outcomes through a unique mechanism that especially benefits subsets of patients, despite side effects and limitations.

Retinoic acid receptor β, a potential therapeutic target in the inhibition of adenovirus replication

Human adenoviruses (HAdVs) usually cause mild respiratory infections, but they can also lead to fatal outcomes for immunosuppressive patients. Unfortunately, there has been no specific anti-HAdV drug approved for medical use. A better understanding of the nature of virus-host interactions during infection is beneficial to the discovery of potential antiviral targets and new antiviral drugs. In this study, a time-course transcriptome analysis of HAdV-infected human lung epithelial cells (A549 cells) was performed to investigate virus-host interactions, and several key host molecules involved in the HAdV infection process were identified. The RARβ (retinoic acid receptor β) molecule, one of the upstream regulatory factors of differentially expressed genes (DEGs), played important roles in HAdV replication. The results of reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting showed that RARβ mRNA and protein were downregulated by HAdV infection in the A549 cells. The knockdown of RARβ by RARβ siRNA increased the HAdV production and the overexpression of RARβ decreased the HAdV production. Furthermore, FDA-approved Tazarotene, which is an RAR selective agonist with relatively more selectivity for RARβ, was found to inhibit HAdV replication in vitro. Taken together, our study presents a key host molecule in adenovirus infection, which could be developed as a potential host target to an anti-adenovirus drug. In addition, this study provides evidence for the re-exploitation of an FDA-approved small molecule for therapeutic applications in adenovirus replication.

Antagonizing Retinoic Acid Receptors Increases Myeloid Cell Production by Cultured Human Hematopoietic Stem Cells

Activities of the retinoic acid receptor (RAR)α and RARγ are important to hematopoiesis. Here, we have investigated the effects of receptor selective agonists and antagonists on the primitive human hematopoietic cell lines KG1 and NB-4 and purified normal human hematopoietic stem cells (HSCs). Agonizing RARα (by AGN195183) was effective in driving neutrophil differentiation of NB-4 cells and this agonist synergized with a low amount (10 nM) of 1α,25-dihydroxyvitamin D3 to drive monocyte differentiation of NB-4 and KG1 cells. Treatment of cultures of human HSCs (supplemented with stem cell factor ± interleukin 3) with an antagonist of all RARs (AGN194310) or of RARα (AGN196996) prolonged the lifespan of cultures, up to 55 days, and increased the production of neutrophils and monocytes. Slowing down of cell differentiation was not observed, and instead, hematopoietic stem and progenitor cells had expanded in number. Antagonism of RARγ (by AGN205728) did not affect cultures of HSCs. Studies of CV-1 and LNCaP cells transfected with RAR expression vectors and a reporter vector revealed that RARγ and RARβ are activated by sub-nM all-trans retinoic acid (EC50-0.3 nM): ~50-fold more is required for activation of RARα (EC50-16 nM). These findings further support the notion that the balance of expression and activity of RARα and RARγ are important to hematopoietic stem and progenitor cell expansion and differentiation.

Chromatin remodeling regulates catalase expression during cancer cells adaptation to chronic oxidative stress

Regulation of ROS metabolism plays a major role in cellular adaptation to oxidative stress in cancer cells, but the molecular mechanism that regulates catalase, a key antioxidant enzyme responsible for conversion of hydrogen peroxide to water and oxygen, remains to be elucidated. Therefore, we investigated the transcriptional regulatory mechanism controlling catalase expression in three human mammary cell lines: the normal mammary epithelial 250MK primary cells, the breast adenocarcinoma MCF-7 cells and an experimental model of MCF-7 cells resistant against oxidative stress resulting from chronic exposure to H₂O₂ (Resox), in which catalase was overexpressed. Here we identify a novel promoter region responsible for the regulation of catalase expression at -1518/-1226 locus and the key molecules that interact with this promoter and affect catalase transcription. We show that the AP-1 family member JunB and retinoic acid receptor alpha (RARα) mediate catalase transcriptional activation and repression, respectively, by controlling chromatin remodeling through a histone deacetylases-dependent mechanism. This regulatory mechanism plays an important role in redox adaptation to chronic exposure to H₂O₂ in breast cancer cells. Our study suggests that cancer adaptation to oxidative stress may be regulated by transcriptional factors through chromatin remodeling, and reveals a potential new mechanism to target cancer cells.

The Retinoid Agonist Tazarotene Promotes Angiogenesis and Wound Healing

Therapeutic angiogenesis is a major goal of regenerative medicine, but no clinically approved small molecule exists that enhances new blood vessel formation. Here we show, using a phenotype-driven high-content imaging screen of an annotated chemical library of 1,280 bioactive small molecules, that the retinoid agonist Tazarotene, enhances in vitro angiogenesis, promoting branching morphogenesis, and tubule remodeling. The proangiogenic phenotype is mediated by retinoic acid receptor but not retinoic X receptor activation, and is characterized by secretion of the proangiogenic factors hepatocyte growth factor, vascular endothelial growth factor, plasminogen activator, urokinase and placental growth factor, and reduced secretion of the antiangiogenic factor pentraxin-3 from adjacent fibroblasts. In vivo, Tazarotene enhanced the growth of mature and functional microvessels in Matrigel implants and wound healing models, and increased blood flow. Notably, in ear punch wound healing model, Tazarotene promoted tissue repair characterized by rapid ear punch closure with normal-appearing skin containing new hair follicles, and maturing collagen fibers. Our study suggests that Tazarotene, an FDA-approved small molecule, could be potentially exploited for therapeutic applications in neovascularization and wound healing.

Retinoic acid receptor signaling preserves tendon stem cell characteristics and prevents spontaneous differentiation in vitrox

Background

Previous studies have reported that adult mesenchymal stem cells (MSCs) tend to gradually lose their stem cell characteristics in vitro when placed outside their niche environment. They subsequently undergo spontaneous differentiation towards mesenchymal lineages after only a few passages. We observed a similar phenomenon with adult tendon stem cells (TSCs) where expression of key tendon genes such as Scleraxis (Scx), are being repressed with time in culture. We hypothesized that an environment able to restore or maintain Scleraxis expression could be of therapeutic interest for in vitro use and tendon cell-based therapies.

Methods

TSCs were isolated from human cadaveric Achilles tendon and expanded for 4 passages. A high content imaging assay that monitored the induction of Scx protein nuclear localization was used to screen ~1000 known drugs.

Results

We identified retinoic acid receptor (RAR) agonists as potent inducers of nuclear Scx in the small molecule screen. The upregulation correlated with improved maintenance of tendon stem cell properties through inhibition of spontaneous differentiation rather than the anticipated induction of tenogenic differentiation. Our results suggest that histone epigenetic modifications by RAR are driving this effect which is not likely only dependent on Scleraxis nuclear binding but also mediated through other key genes involved in stem cell self-renewal and differentiation. Furthermore, we demonstrate that the effect of RAR compounds on TSCs is reversible by revealing their multi-lineage differentiation ability upon withdrawal of the compound.

Conclusion

Based on these findings, RAR agonists could provide a valid approach for maintaining TSC stemness during expansion in vitro, thus improving their regenerative potential for cell-based therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0306-3) contains supplementary material, which is available to authorized users.

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.

Possible roles of barrier-to-autointegration factor 1 in regulation of keratinocyte differentiation and proliferation

BACKGROUND

Barrier-to-autointegration factor 1 (BANF1) is an essential component of the nuclear lamina. Recent studies have clarified that BANF1 is a causative molecule of Nestor-Guillermo progeria syndrome. Despite recent progress in studies on BANF1, the role of BANF1 in keratinocytes has not been addressed at all.

OBJECTIVE

This study aims to determine the localization of BANF1 in psoriatic epidermal keratinocytes as well as in normal keratinocytes and to clarify its possible function in those keratinocytes.

METHODS

Immunohistochemistry of BANF1 was performed on 10 cases of psoriasis and 10 healthy control individuals. Expression of molecules associated with inflammation of the skin by HSC-1, a human skin squamous cell carcinoma cell line, stimulated by TPA and treated with siRNA to BANF1 were analyzed with quantitative PCR and Western blot.

RESULTS

Strong nuclear-dominant immunostaining of BANF1 was seen in the epidermal keratinocytes of psoriatic lesions, although in the normal epidermis, all the KCs in the upper epidermis showed cytoplasmic-dominant staining of BANF1. By BANF1 knockdown in TPA-stimulated HSC-1 cells, the mRNA levels of S100A9 were significantly elevated compared with those of control HSC-1 cells treated with siRNA to CD4. The protein expression level of S100A9 and phosphorylated c-Jun was elevated by BANF1 knockdown.

CONCLUSION

BANF1 is translocated onto the nuclear envelope in the psoriatic epidermal keratinocytes, suggesting that BANF1 is associated with upregulated proliferation of keratinocytes in psoriatic lesions. Activation of BANF1 possibly suppresses S100A9 expression and inactivates c-Jun, resulting in suppression of cutaneous inflammation.

A comparison of the roles of peroxisome proliferator-activated receptor and retinoic acid receptor on CYP26 regulation

The cytochrome P450 26 family is believed to be responsible for all-trans-retinoic acid (atRA) metabolism and elimination in the human fetus and adults. CYP26A1 and CYP26B1 mRNA is expressed in a tissue-specific manner, and mice in which the CPY26 isoform has been knocked out show distinct malformations and lethality. The aim of this study was to determine differences in CYP26A1 and CYP26B1 regulation and expression. Analysis of CYP26A1 and CYP26B1 expression in a panel of 57 human livers showed CYP26A1 to be the major CYP26 isoform present in the liver, and its expression to be subject to large interindividual variability between donors. CYP26A1 and retinoic acid receptor (RAR) beta were found to be greatly inducible by atRA in HepG2 cells, whereas CYP26B1, RARalpha, and RARgamma were induced to a much lesser extent. Based on treatments with RAR isoform-selective ligands, RARalpha is the major isoform responsible for CYP26A1 and RARbeta induction in HepG2 cells. Classic cytochrome P450 inducers did not affect CYP26 transcription, whereas the peroxisome proliferator-activated receptor (PPAR) gamma agonists pioglitazone and rosiglitazone up-regulated CYP26B1 transcription by as much as 209- +/- 80-fold and CYP26A1 by 10-fold. RARbeta was also up-regulated by pioglitazone and rosiglitazone. CYP26B1 induction by PPARgamma agonists was abolished by the irreversible PPARgamma antagonist 2-chloro-5-nitrobenzanilide (GW9662), whereas RARbeta and CYP26A1 induction was unaffected by GW9662. Overall, the results of this study suggest that CYP26B1 and CYP26A1 are regulated by different nuclear receptors, resulting in tissue-specific expression patterns. The fact that drugs can alter the expression of CYP26 enzymes may have toxicological and therapeutic importance.

Topical retinoids in the treatment of acne vulgaris

Topical retinoids are highly effective in the treatment of both comedonal and inflammatory lesions of acne and are a vital part of almost any acne regimen. A better understanding of the structure and function of this class of medications has led to better outcomes in treatments of patients with acne. In this article, the structure and function of retinoids is first reviewed. Then, the clinical effectiveness and tolerability of each of the available topical retinoid formulations is summarized.

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.

Retinoids in the treatment of skin aging: an overview of clinical efficacy and safety

Aging of skin is an intricate biological process consisting of two types. While intrinsic or chronological aging is an inevitable process, photoaging involves the premature aging of skin occurring due to cumulative exposure to ultraviolet radiation. Chronological and photoaging both have clinically differentiable manifestations. Various natural and synthetic retinoids have been explored for the treatment of aging and many of them have shown histological and clinical improvement, but most of the studies have been carried out in patients presenting with photoaged skin. Amongst the retinoids, tretinoin possibly is the most potent and certainly the most widely investigated retinoid for photoaging therapy. Although retinoids show promise in the treatment of skin aging, irritant reactions such as burning, scaling or dermatitis associated with retinoid therapy limit their acceptance by patients. This problem is more prominent with tretinoin and tazarotene whereas other retinoids mainly represented by retinaldehyde and retinol are considerably less irritating. In order to minimize these side effects, various novel drug delivery systems have been developed. In particular, nanoparticles have shown a good potential in improving the stability, tolerability and efficacy of retinoids like tretinoin and retinol. However, more elaborate clinical studies are required to confirm their advantage in the delivery of topical retinoids.

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.

Receptors in Skin Ageing and Antiageing Agents

Skin ageing is an irreversible process during which ultrastructural and physiologic alterations happen. Dermatology has focused a lot of attention on the reversal of signs of ageing and photodamage, with the purposes of achieving cosmetic benefits and preventing photocancerogenesis. Recent advances in skin biology have clarified the mechanisms by which photoageing occurs and have given rise to new treatments to prevent and reverse this process. The understanding of the role of key receptors involved in the complex pathomechanism of skin ageing probably will lead to the development of the new therapeutic agents in the near future.

Topical immunomodulation: modes of action with clinical correlation

Many classes and preparations of immunomodulators are available to the clinician, serving as stimulatory or inhibitory influences on a variety of disease states. To maximize their efficacy, it is important for the clinician to take a step back from the usual routine of treating symptoms and consider the immune processes that took place to create inflammation, tumors, or responses to infections. From there, after considering the short-term and long-term consequences of the treatment, one can match the immune profile of the disease to the treatment. Most importantly, immunomodulators provide the opportunity to do what is best for the patient at that time, as well as for control of the future of the disease, whether it is acute or chronic.

Srcasm overexpression in psoriasis-insights into pathogenesis

BACKGROUND

Psoriasis is a prevalent, chronic cutaneous disorder associated with a T-cell lymphocytic infiltrate and altered keratinocyte growth. Some of the molecular features of enhanced keratinocyte growth include increased growth factor receptor activation leading to enhanced cellular tyrosine kinase activity. Receptor tyrosine kinases, including the epidermal growth factor (EGF) receptor, are important regulators of keratinocyte growth, and increased activity of this receptor has been detected in psoriasis. A recently discovered, novel regulator of Src tyrosine kinases, termed Src-activating and signaling molecule (Srcasm), has been shown to modulate EGF signaling and promote differentiation in human keratinocytes. Given the properties of Srcasm, it would be of interest to characterize its expression in psoriasis. In this study, the levels of Srcasm mRNA and protein are characterized, and the relationship of these experimental observations to the psoriasis pathogenesis is discussed.

METHODS

The levels of Srcasm mRNA were determined by quantitative reverse transcriptase polymerase chain reaction (RT-PCR) on RNA isolated from unremarkable and lesional patient tissue. These data were supplemented by performing radioactive in situ hybridization on formalin-fixed biopsy specimens of psoriatic lesions and unremarkable epidermis. Expression of Srcasm protein was evaluated by protein immunohistochemistry and Western blotting of protein lysates derived from patient samples.

RESULTS

All experimental modalities show that levels of Srcasm mRNA and protein were elevated in psoriatic lesions compared to unremarkable epidermis.

CONCLUSIONS

Increased levels of Srcasm mRNA and protein are seen in psoriasis. Given what is known regarding Srcasm function, increased levels of this molecule in keratinocytes may represent a cell compensatory mechanism that is primed to re-establish a physiologic differentiation program.

Effect of all-trans retinoic acid on sodium/iodide symporter expression, radioiodine uptake and gene expression profiles in a human anaplastic thyroid carcinoma cell line

The plasma membrane glycoprotein sodium/iodide symporter (NIS) is crucial for thyroid hormone biosynthesis and mediates the iodide uptake of thyrocytes. It has been shown that retinoic acid (RA) alters NIS gene expression in thyroid carcinoma lines and stimulates their iodide uptake. Here, we generated an ARO human thyroidal cancer cell line that expresses the NIS gene (ARO-NIS) and found that its baseline 125I uptake was threefold higher than that of its parental ARO cells. However, a 1-microM all-trans retinoic acid (tRA) treatment significantly increased this 125I uptake up to approximately approximately 6.5-fold on Day 3. tRA also elevated NIS mRNA expression in ARO-NIS cells, with peaks of expression being observed on Day 3. To investigate the underlying genomic mechanisms involved in these tRA-induced phenotypic changes, we subjected tRA-treated and untreated ARO-NIS cells to cDNA microarray analysis. Of 1152, genes spotted onto the microarray membrane, 18 were up-regulated (z ratio>2.0) and 33 were down-regulated (z ratio<-2.0) in ARO-NIS cells after 3 days of tRA treatment. More specifically, tRA increased the expression of BCL3, CSRP3, v-fos, and CDK5 genes and decreased the expression of the FGF12 and IGFBP6 genes. Thus, tRA treatment of human anaplastic thyroid carcinoma cells stably expressing the NIS gene significantly elevates their NIS-mediated radioiodine uptake and alters the expression of many genes involved in cell growth and cellular differentiation. Therefore, tRA treatment and NIS gene transfection are potential tools for the diagnosis and treatment of thyroid cancer.

Update on retinoid therapy of psoriasis in: an update on the use of retinoids in dermatology

Both in the topical and systemic treatment of psoriasis, retinoids are mainstays. In this chapter the history and modes of actions of retinoids are presented. Tazarotene and acitretin are the only retinoids that are available in both topical and systemic formulations. A more extensive description of their pharmacology, modes of action, indications and contraindications, clinical results, and treatment strategies will be presented. Finally, retinoid X receptor ligands and retinoic acid metabolism blocking agents will be introduced as potential future retinoid mimetics in psoriasis.

Photoaging: Mechanisms and repair

Aging is a complex, multifactorial process resulting in several functional and esthetic changes in the skin. These changes result from intrinsic as well as extrinsic processes, such as ultraviolet radiation. Recent advances in skin biology have increased our understanding of skin homeostasis and the aging process, as well as the mechanisms by which ultraviolet radiation contributes to photoaging and cutaneous disease. These advances in skin biology have led to the development of a diversity of treatments aimed at preventing aging and rejuvenating the skin. The focus of this review is the mechanism of photoaging and the pathophysiology underlying the treatments specifically designed for its prevention and treatment.

LEARNING OBJECTIVES

At the conclusion of this learning activity, participants should be familiar with the mechanism of photoaging, the treatments for photoaging, and the data that supports the use of these treatments.

Retinoid-mediated stimulation of steroid sulfatase activity in myeloid leukemic cell lines requires RARalpha and RXR and involves the phosphoinositide 3-kinase and ERK-MAP kinase pathways

All-trans retinoic acid and 9-cis-retinoic acid stimulate the activity of steroid sulfatase in HL60 acute myeloid leukemia cells in a concentration- and time-dependent manner. Neither of these 'natural retinoids' augmented steroid sulfatase activity in a HL60 sub-line that expresses a dominant-negative retinoic acid receptor alpha (RARalpha). Experiments with synthetic RAR and RXR agonists and antagonists suggest that RARalpha/RXR heterodimers play a role in the retinoid-stimulated increase in steroid sulfatase activity. The retinoid-driven increase in steroid sulfatase activity was attenuated by inhibition of phospholipase D (PLD), but not by inhibitors of phospholipase C. Experiments with inhibitors of protein kinase C (PKC) show that PKCalpha and PKCdelta play an important role in modulating the retinoid-stimulation of steroid sulfatase activity in HL60 cells. Furthermore, we show that pharmacological inhibition of the RAF-1 and ERK MAP kinases blocked the retinoid-stimulated increase in steroid sulfatase activity in HL60 cells and, by contrast, inhibition of the p38-MAP kinase or JNK-MAP kinase had no effect. Pharmacological inhibitors of the phosphatidylinositol 3-kinase, Akt, and PDK-1 also abrogated the retinoid-stimulated increase in steroid sulfatase activity in HL60 cells. These results show that crosstalk between the retinoid-stimulated genomic and non-genomic pathways is necessary to increase steroid sulfatase activity in HL60 cells.

Disposition and Biotransformation of the Acetylenic Retinoid Tazarotene in Humans

Oral tazarotene, an acetylenic retinoid, is in clinical development for the treatment of psoriasis. The disposition and biotransformation of tazarotene were investigated in six healthy male volunteers, following a single oral administration of a 6 mg (100 microCi) dose of [14C]tazarotene, in a gelatin capsule. Blood levels of radioactivity peaked 2 h postdose and then rapidly declined. Total recovery of radioactivity was 89.2+/-8.0% of the administered dose, with 26.1+/-4.2% in urine and 63.0+/-7.0% in feces, within 7 days of dosing. Only tazarotenic acid, the principle active metabolite formed via esterase hydrolysis of tazarotene, was detected in blood. One major urinary oxidative metabolite, tazarotenic acid sulfoxide, accounted for 19.2+/-3.0% of the dose. The majority of radioactivity recovered in the feces was attributed to tazarotenic acid representing 46.9+/-9.9% of the dose and only 5.82+/-3.84% of dose was excreted as unchanged tazarotene. Thus following oral administration, tazarotene was rapidly absorbed and underwent extensive hydrolysis to tazarotenic acid, the major circulating species in the blood that was then excreted unchanged in feces. A smaller fraction of tazarotenic acid was further metabolized to an inactive sulfoxide that was excreted in the urine.

Differential regulation of sodium/iodide symporter gene expression by nuclear receptor ligands in MCF-7 breast cancer cells

The sodium/iodide symporter (NIS) mediates iodide uptake in lactating breast tissue and is expressed in some breast cancers. We have previously demonstrated that all-trans retinoic acid (tRA) stimulates NIS gene expression and the selective cytotoxic effect of beta-emitting radioiodide-131 ((131)I) in both in vitro and in vivo MCF-7 breast cancer cell systems. We studied the ability of natural and synthetic retinoids, in combination with other nuclear receptor ligands, to achieve greater and more sustained induction of NIS in MCF-7 cells and enhance (131)I-mediated cytotoxicity. Selective stimulation of retinoic acid receptor (RAR) beta/gamma produced marked NIS induction; and selective stimulation of RARalpha, RARgamma, or retinoid X receptor produced more modest induction. Maximal NIS induction was seen with 9-cis retinoic acid and AGN190168, a RAR beta/gamma-agonist. Dexamethasone (Dex), but not the other nuclear receptor ligands, in combination with tRA synergistically induced iodide uptake and NIS mRNA expression, predominantly by prolonging NIS mRNA half-life. The addition of Dex reduced the EC(50) of tRA for NIS stimulation to approximately 7%, such that 10(-7) m tRA with addition of Dex enhanced iodide uptake and selective cytotoxicity of (131)I greater than 10(-6) m tRA alone. AGN190168 combined with Dex synergistically increased iodide uptake and significantly prolonged induction (5 d) of iodide uptake compared with that induced by the combination of tRA/Dex or 9-cis retinoic acid/Dex. The addition of Dex reduced the effective dose of retinoid and prolonged the induction of NIS, especially with AGN190168, suggesting higher efficacy of (131)I after combination treatment.

Development of a gas chromatography method for the determination of isotretinoin and its degradation products in pharmaceuticals

This paper describes the development of a gas chromatography (GC) method used for the assay of isotretinoin in its isolated form and in pharmaceutical formulations. Isotretinoin soft and hard gelatin capsules were prepared with various excipients. The performance of the proposed gas chromatography method was compared to that of traditional high performance liquid chromatography (HPLC) systems for this substance, and the GC parameters were established based on several preliminary tests, including thermal analysis of isotretinoin. Results showed that gas chromatography-flame ionization detector (GC-FID) exhibited a separation efficiency superior to that of HPLC, particularly for separating isotretinoin degradation products. This method was proven to be effectively applicable to stability evaluation assays of isotretinoin and isotretinoin based pharmaceuticals.

Transcriptional activities of retinoic acid receptors

Vitamin A derivatives plays a crucial role in embryonic development, as demonstrated by the teratogenic effect of either an excess or a deficiency in vitamin A. Retinoid effects extend however beyond embryonic development, and tissue homeostasis, lipid metabolism, cellular differentiation and proliferation are in part controlled through the retinoid signaling pathway. Retinoids are also therapeutically effective in the treatment of skin diseases (acne, psoriasis and photoaging) and of some cancers. Most of these effects are the consequences of retinoic acid receptors activation, which triggers transcriptional events leading either to transcriptional activation or repression of retinoid-controlled genes. Synthetic molecules are able to mimic part of the biological effects of the natural retinoic acid receptors, all-trans retinoic acid. Therefore, retinoic acid receptors are considered as highly valuable therapeutic targets and limiting unwanted secondary effects due to retinoid treatment requires a molecular knowledge of retinoic acid receptors biology. In this review, we will examine experimental evidence which provide a molecular basis for the pleiotropic effects of retinoids, and emphasize the crucial roles of coregulators of retinoic acid receptors, providing a conceptual framework to identify novel therapeutic targets.

Differential regulation of Cu, Zn- and Mn-superoxide dismutases by retinoic acid in normal and psoriatic human fibroblasts

Superoxide dismutases' (SODs) expression is altered in several diseases including Alzheimer, atherosclerosis, cancer and psoriasis. Previously, we reported a marked increase in Mn-SOD and Cu,Zn-SOD functional activity in human dermal psoriatic fibroblasts. As retinoic acid (RA) has been used in the treatment of psoriasis and a mechanism for its beneficial effects is not understood, we investigated the effects of RA on SOD mRNA and protein expression levels in human normal and psoriatic fibroblasts. Prior to RA exposure, Cu,Zn-SOD protein and mRNA levels were similar in normal compared to psoriatic fibroblasts while Mn-SOD protein and mRNA levels were increased in psoriatic cells. However, in contrast to normal fibroblasts, exposure of psoriatic fibroblasts to 1 microM RA down-regulated Mn-SOD mRNA, and also decreased Mn-SOD activity by approximately 80% with no change in Mn-SOD protein levels. In contrast, Cu,Zn-SOD protein and enzymatic activity were modestly reduced by RA treatment in both normal and psoriatic fibroblasts. Furthermore, RA treatment of psoriatic fibroblasts also caused a decrease in Cu,Zn-SOD steady-state mRNA levels. These results indicate that RA can serve as a regulatory agent to down-regulate the steady-state levels of both Mn-SOD and Cu,Zn-SOD in psoriatic cells. These findings offer a new model for the antiinflammatory activity of RA when used in the treatment of psoriasis.

Novel pharmacological approaches in the treatment of psoriasis

Progress in the understanding of psoriasis as a T-cell mediated inflammatory disease has led to the development of new immunomodulatory therapies. Currently the main focus is on the so-called biologics (or biological agents), including fusion proteins, monoclonal antibodies, cytokines and selective receptors. They mainly target single steps in the complex cascade of humoral and cellular inflammatory immuno-mechanisms that finally lead to the accelerated growth of epidermal and vascular cells in the psoriatic lesions. The most promising and advanced biological agents are discussed along with their influence on the critical pathophysiological steps in psoriasis, including depletion of T cells, blockade of initial T-cell activation and T-cell receptor (TCR) stimulation, blockade of costimulatory signals and T-cell proliferative signals as well as restoration of the T helper type 1 (Th1)/Th2 balance by diminishing type 1 cytokines and administration of type 2 cytokines. In addition to the biological agents, further development of 'classical' dermatological therapies, such as retinoids, or the discovery of new indications for non-dermatological agents contribute to the novel pharmacological approaches in the treatment of psoriasis.

Topical tazarotene: a review of its use in the treatment of plaque psoriasis

Tazarotene (Tazorac) is a topical retinoid indicated for the treatment of plaque psoriasis. When used as monotherapy, topical tazarotene was effective at controlling signs and symptoms of plaque psoriasis, and had significantly lower post-treatment relapse rates than fluocinonide cream. The most common adverse events associated with tazarotene therapy are skin-associated events, such as pruritus, burning, and erythema. Combination therapy with tazarotene and mid-to-high potency topical corticosteroids generally resulted in a greater therapeutic effect than that with tazarotene alone, reduced the irritancy of tazarotene, and decreased the risk of post-treatment disease flare seen with corticosteroids; it also has the potential to reduce the degree of skin atrophy associated with topical corticosteroids. The combination of tazarotene and phototherapy also appears promising. Thus, tazarotene, as monotherapy or in combination with topical corticosteroids or UV light therapy, represents a useful treatment option in patients with plaque psoriasis.

A retinoic acid receptor beta/gamma-selective prodrug (tazarotene) plus a retinoid X receptor ligand induces extracellular signal-regulated kinase activation, retinoblastoma hypophosphorylation, G0 arrest, and cell differentiation

Retinoic acid receptor (RAR)beta is perceived to function as a tumor suppressor gene in various contexts where its absence is associated with tumorigenicity and its presence causes cell cycle arrest. Tazarotene is a prodrug selective for RARbeta/gamma, thereby motivating interest in determining whether tazarotene might activate putative tumor suppressor activity. Using HL-60 human myeloblastic leukemia cells, a cell line that undergoes G0 cell cycle arrest and myeloid differentiation in response to retinoic acid (RA), tazarotene failed to cause extracellular signal-regulated kinase (ERK) activation, a requirement for retinoic acid (RA)-induced G0 arrest and differentiation; retinoblastoma (RB) hypophosphorylation, another characteristic of RA-induced G0 arrest and cell differentiation; G0 arrest; or differentiation into mature myeloid cells. However, when used in combination with a retinoid X receptor (RXR)-selective ligand, tazarotene caused ERK activation, RB tumor suppressor protein hypophosphorylation, G0 arrest, and myeloid differentiation. The kinetics of G0 arrest and differentiation was similar to that of RA. Dose-response studies showed that diminishing tazarotene progressively diminished both induced cell differentiation and G0 arrest, where the doses for cellular effects were consistent with the transcriptional transactivation data. For either tazarotene or an RARalpha-selective ligand, diminishing the coadministered RXR-selective ligand diminished both induced differentiation and G0 arrest. Tazarotene could propel either early or late portions of the period leading to differentiation and G0 arrest and was interchangeable with an RARalpha-selective ligand. Tazarotene used with RXR-selective ligand may thus be a useful antineoplastic agent in differentiation induction therapy as exemplified by the prototypical RA treatment of acute promyelocytic leukemia.

The p73 gene is an anti-tumoral target of the RARbeta/gamma-selective retinoid tazarotene

Tazarotene, a member of the new class of acetylenic retinoids, has been shown to be effective in the treatment of several hyperproliferative skin diseases, including non-melanoma skin cancer. Its effectiveness is thought to rely on the ability to activate retinoic acid receptors beta and gamma and to induce a number of downstream anti-proliferative genes. Here, we show that the p53-related gene p73 is a target of tazarotene. Indeed, tazarotene modulates the expression of the p73 gene in immortalized keratinocyte cell lines by inducing the pro-apoptotic and anti-proliferative TAp73 isoforms and by repressing the anti-apoptotic and pro-proliferative DeltaNp73 isoforms. This occurs at the transcriptional level through a coordinated action on P1p73 and P2p73 promoters that control the expression of TA and DeltaN isoforms, respectively. The selective downregulation of DeltaNp73 expression by small interfering RNA led to an enhancement of tazarotene-induced bax activation and apoptosis, whereas the downregulation of both TA and DeltaN isoforms impairs tazarotene-mediated apoptosis. These results indicate the relevance of p73 gene products in tazarotene-induced growth inhibition and effectiveness in the treatment of skin tumors.

Effects of tazarotene 0.1 % cream in the treatment of facial acnevulgaris: Pooled results from two multicenter, double-blind, randomized, vehicle-controlled, parallel-group trials

BACKGROUND

Topical retinoids are one of the most effective classes of topical drugs used to treat acne vulgaris. The effects of the gel formulation of the topical retinoid tazarotene have been widely reported, but few data on the cream formulation are available.

OBJECTIVE

The primary aim of the 2 studies reported in this article was to determine the effects of tazarotene 0.1 % cream in patients with facial acne vulgaris.

METHODS

Two randomized, double-blind, parallel-group studies were performed. The first was conducted at 14 investigational sites across the United States, and the second took place at 15 sites, with 5 of these providing blood samples for analysis of tazarotenic acid. In both studies, patients aged > or =12 years with facial acne vulgaris were randomized to receive tazarotene or vehicle cream QD for 12 weeks. Lesion counts (noninflammatory, inflammatory, and total) and overall clinical and global assessments were made at weeks 0 (baseline), 4, 8, and 12. Adverse events (AEs) were monitored throughout the study In one of the studies, therapeutic drug monitoring was performed at weeks 4 and 8 in members of the study population who gave consent for blood withdrawal.

RESULTS

Eight hundred forty-seven patients were enrolled in the 2 studies (430 males, 417 females; mean age,19 years; age range, 11-52 years [1 patient was entered into the study at age 11 years, in violation of the protocol]). At 12 weeks, the median percentage changes from baseline in all 3 lesion counts were significantly lower with tazarotene than with vehicle (all, P < 0.001), as were the overall clinical and global responses (both, P < 0.001). Treatment-related AEs whose incidence was higher with tazarotene than with vehicle included desquamation, dry skin, erythema, a burning sensation on the skin, and skin irritation (all, P < 0.001) and pruritus (P < 0.01); most (83%-98%) were mild or moderate. Systemic exposure to tazarotenic acid was limited (mean, <0.1 ng/mL) and did not increase with time.

CONCLUSIONS

In these 2 studies in adolescent and adult patients with facial acne vulgaris, tazarotene 0.1%cream QD for 12 weeks was effective and well tolerated. Systemic exposure to tazarotenic acid was limited.

Tazarotene: therapeutic strategies in the treatment of psoriasis, acne and photoaging

Tazarotene is a member of the new generation of receptor-selective, synthetic retinoids for the topical treatment of mild to moderate plaque psoriasis, acne vulgaris and photoaging. Though they are effective in monotherapy, clinical studies with a focus on novel combination treatments and a comparison of different agents for these skin disorders are accumulating. The concomitant use of tazarotene with a mid-potency or high-potency corticosteroid enhances the efficacy in psoriatic plaques and reduces the risk of steroid-induced skin atrophy. Combining phototherapy with adjunctive tazarotene accelerates the clinical response and reduces the cumulative UVB or PUVA exposure load. Tazarotene applied once daily is superior to adapalene monotherapy in acne vulgaris and is efficacious in the treatment of photodamage. Novel therapeutic regimens such as short-contact therapy have been developed for both acne and psoriasis in order to diminish the major adverse events like pruritus, burning, local skin irritation and erythema.

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)

Possible role of Malassezia furfur in psoriasis: modulation of TGF-beta1, integrin, and HSP70 expression in human keratinocytes and in the skin of psoriasis-affected patients

BACKGROUND

Psoriasis is a disease characterized by an abnormal pattern of keratinocyte growth and differentiation. Malassezia furfur forms part of the normal human skin flora. It may also be involved in the pathogenesis of psoriasis. To define the role of M. furfur in the pathogenesis of psoriasis, we investigated how M. furfur regulates molecules involved in cell migration and proliferation. The experiments were performed using human keratinocytes and skin biopsies from M. furfur-positive and -negative psoriasis-affected patients. In addition, we examined the signal transduction mechanisms involved.

MATERIALS AND METHODS

Western blot analysis was performed on human keratinocytes lysates treated or untreated with M. furfur and on biopsies from healthy and psoriasis patients. Signal transduction mechanisms involved were evaluated by electrophoretic mobility shift assay using the AP-1 inhibitor curcumin.

RESULTS

We found that M. furfur up-regulates transforming growth factor-beta1 (TGF-beta1), integrin chain, and HSP70 expression in human keratinocytes via AP-1-dependent mechanism. In the biopsies of M. furfur-positive psoriasis-affected patients, an increase in TGF-beta1, integrin chains, and HSP70 expression was found.

CONCLUSION

Our data suggest that M. furfur can induce the overproduction of molecules involved in cell migration and hyperproliferation, thereby favoring the exacerbation of psoriasis.

Management of the primary cutaneous lymphomas

Cutaneous lymphomas are rare and, although some are a manifestation of systemic lymphoma, the majority arise primarily from the skin. These primary cutaneous lymphomas comprise both T- and B-cell subtypes and represent a wide spectrum of disorders, which at times can be difficult to diagnose and classify. Classical therapeutic strategies include topical corticosteroids, phototherapy, radiotherapy, retinoids, extracorporeal photopheresis, topical chemotherapy, systemic chemotherapy and biological response modifiers. Newer therapies include the synthetic retinoid bexarotene, the immunotoxin conjugate denileukin diftitox, interleukin-12 and monoclonal antibodies such as alemtuzumab and rituximab.

Efficacy validation of synthesized retinol derivatives In vitro: stability, toxicity, and activity

Retinol (vitamin A) is used as an antiwrinkle agent in the cosmetics industry. However, its photo-instability makes it unsuitable for use in general cosmetic formulations. To improve the photo-stability of retinol, three derivatives (3, 4, and 5) were synthesized and their biological activities were analyzed. 1H NMR and HPLC analysis indicated that derivatives 3 and 5 were much more stable than retinol under our sunlight exposure conditions. When human adult fibroblasts were treated, the IC(50) of derivative 3 was 96 microM, which is similar to that of retinol, as determined by the MTT assay. Derivatives 4 and 5 were 2.5 and 8 times more toxic than retinol, respectively. At 1 microM treatment, like retinol, derivatives 3 and 4 were specifically active for RARalpha out of six retinoid receptors (RAR/RXRalpha, beta, gamma). Dose-dependent analysis confirmed that derivative 4 was as active as retinol and the other two derivatives were less active for RARalpha. The effect of our derivatives on the expression of collagenase, an indicator of wrinkle formation, was measured using the transient co-expression of c-Jun and RT-PCR in HaCaT cells. Collagenase promoter activity, which is increased by c-Jun expression, was reduced 42% by retinol treatment. The other derivatives inhibited collagenase promoter activity similarly. These results were further confirmed by RT-PCR analysis of the collagenase gene. Taken together, our results suggest that retinol derivative 3 is a promising antiwrinkle agent based on its higher photo-stability, lower RARalpha activity (possibly indicating reduced side effects), and similar effect on collagenase expression.

Aberrant signalling and transcription factor activation as an explanation for the defective growth control and differentiation of keratinocytes in psoriasis: a hypothesis

Psoriasis is a chronic inflammatory skin disease characterized by the accumulation of red, scaly plaques on the skin. The plaques result from hyperproliferation and incomplete differentiation of keratinocytes (KC) in a process that seems to be driven, in part by skin-infiltrating leucocytes. We believe that the KC have inherent defects in intracellular signalling which could be usefully targeted to allow the development of more effective therapies. We suggest that there are defects in the regulation of the transcription factors: signal transducer and activator of transcription (STAT-1alpha), interferon regulated factor-1 (IRF-1) and NFkappaB which lead to loss of growth and differentiation control when the cells are subjected to physico-chemical and immunological stress. We also highlight recent studies that suggest that peroxisome proliferator-activated receptors, the notch receptor and defects in calcium and other ion transporting proteins may contribute to impairment in the ability of psoriatic KC to differentiate. The role of these systems in the development of the psoriatic phenotype and tests of these hypotheses are proposed.