Tazarotene-induced gene 3 is suppressed in basal cell carcinomas and reversed in vivo by tazarotene application

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.

A review of emerging and non-US FDA-approved topical agents for the treatment of basal cell carcinoma

Although surgical therapy continues to be the gold standard for the treatment of basal cell carcinoma given high cure rates and the ability to histologically confirm tumor clearance, there are a number of nonsurgical treatment options that may be considered based on individual tumor characteristics, functional and cosmetic considerations, patient comorbidities and patient preference. Topical 5-fluorouracil 5% cream and imiquimod 5% cream have been US FDA-approved for the treatment of superficial basal cell carcinoma. Additionally, a number of new and emerging topical agents and techniques have been described for the treatment of basal cell carcinoma and will be reviewed herein.

Immunohistochemical expression of Tazarotene-induced Gene 3 in oral squamous cell carcinoma

BACKGROUND

The prognosis of hyperproliferative skin lesions, such as psoriasis, basal cell carcinoma, and non-melanoma skin cancers, is significantly benefited from the levels of tazarotene-induced gene-1 (TIG3) expression and subsequent treatment with tazarotene. Such observations suggest that TIG3 could be used as a biomarker for apoptosis, differentiation, and proliferation. The current study aimed to evaluate the expression of TIG3 in normal oral mucosa (NOM) and oral squamous cell carcinoma (OSCC) compared with normal skin (NS) and skin squamous cell carcinoma (SSCC) using immunohistochemistry.

METHODS

Seventeen cases each of SSCC, OSCC, NOM, and NS were evaluated. Each section was immunohistochemically stained with a rabbit polyclonal TIG3 antibody. The entire procedure was blinded and evaluated by 5 observers. Statistical analysis was performed using the chi-square test.

RESULTS

There was a significant decrease in TIG3 protein expression in OSCC and SSCC compared with that in NOM and NS (P = 0.008). The progressive loss of expression was observed as the grade of both malignancies increased. However, there was no significant difference in the expression among the normal tissue groups and within SCC groups of similar grades.

CONCLUSION

The present study suggests that the loss of TIG3 is an important event in carcinogenesis. TIG3 acts as a regulator of keratinocyte proliferation and terminal differentiation. Therefore, TIG3 could be a potential biomarker to differentiate aggressive and non-aggressive neoplasms.

Beyond Mohs surgery and excisions: A focused review of treatment options for subtypes of basal cell carcinoma

Basal cell carcinoma (BCC) is the most common nonmelanoma skin cancer. It originates from undifferentiated cells in the basal cell layer of the epidermis or from the outer root sheath of the hair follicle. The most important factor in development of BCC is ultraviolet radiation. Surgery is considered the gold standard of treatment for BCC. However, nonsurgical options are available for individuals who are unsuitable for surgery. The purpose of this review is to summarize the efficacy and indications of alternative, nonsurgical treatments that can be used in the management of BCC. An extensive literature review was performed for the nonsurgical options for the treatment of BCC. Resources searched included PubMed and Google Scholars, limited to the years 1995 to 2020. Key words searched included BCC, destructive methods, photodynamic therapy (PDT), radiotherapy, topical medication, laser, hedgehog pathway inhibitors (HPIs). The most relevant results such as systematic reviews, randomized controlled trials, or comparative studies were selected to provide a summary for the most common nonsurgical methods used for treating BCC. Effective nonsurgical treatments for BCC include destructive methods (eg, curettage alone, cryosurgery, or electrodessication), PDT, topical medications, radiotherapy, laser, and HPIs. Nonsurgical therapeutic alternatives are safe and effective for the treatment of BCC. Factors such as tumor location, size, and histopathological subtype should be taken into consideration when selecting optimal treatment. In addition to clinical factors, cosmetic results and patient preference should be considered.

Basal cell carcinoma: Contemporary approaches to diagnosis, treatment, and prevention

As the most common human cancer worldwide and continuing to increase in incidence, basal cell carcinoma is associated with significant morbidity and cost. Continued advances in research have refined both our insight and approach to this seemingly ubiquitous disease. This 2-part continuing medical education series provides a comprehensive and contemporary review of basal cell carcinoma. The second article in this series will present both the current standard of care and newly developed approaches to diagnosis, treatment, and prevention of this disease.

VS-5584 mediates potent anti-myeloma activity via the upregulation of a class II tumor suppressor gene, RARRES3 and the activation of Bim

The PI3K/mTOR/AKT pathway is an integral regulator of survival and drug resistance in multiple myeloma (MM). VS-5584 was synthesized with dual-specific and equipotent activity against mTORC1/2 and all four Class I PI3K isoforms so as to durably inhibit this pathway. We show that VS-5584 is highly efficacious against MM cell lines even in the presence of IL-6 and IGF-1 and that this growth inhibition is partially dependent on Bim. Importantly, VS-5584 triggers apoptosis in patient cells with a favorable therapeutic index. Gene expression profiling revealed a VS-5584-induced upregulation of RARRES3, a class II tumor suppressor gene. MM patient databases, UAMS and APEX, show that RARRES3 is under-expressed in 11q13 subsets which correlates with the reduced effectiveness of VS-5584 in 11q13 cell lines. Silencing RARRES3 expression significantly rescues VS-5584-induced cell death and increases cyclin D2 expression but not cyclin D1 or other cyclins implying a role for RARRES3 in cell cycle arrest. In vivo, VS-5584 significantly reduces the tumor burden of MM mouse xenografts. We further identified that VS-5584 synergised with Dexamethasone, Velcade, and exceptionally so with HDAC inhibitor, Panobinostat. Interestingly, this was consistently observed in several patient samples, proposing a promising novel clinical strategy for combination treatment especially in relapsed/refractory patients.

Chemoprevention of Keratinocyte Carcinomas: An Updated Review

A well-established link between ultraviolet exposure and the carcinogenesis of keratinocyte carcinomas exists. Despite increased sun protection efforts, skin cancer remains the most common cancer in the USA. Numerous studies on the topic of chemoprevention investigate alternative topical, oral, and injectable agents to reduce skin cancer incidence in those at risk. Such agents include sunscreen, numerous vitamins and minerals, difluoromethylornithine, non-steroidal anti-inflammatory drugs, various peptides, field therapy, statins, and polyphenols. In this focused review, we discuss the risks and benefits of chemoprotective agents reported in clinical studies conducted in humans. We report several agents that may reduce skin cancer incidence in those at risk.

Topical Retinoids: Therapeutic Mechanisms in the Treatment of Photodamaged Skin

Retinoids are a group of substances comprising vitamin A and its natural and synthetic derivatives. Retinoids were first used in dermatology in 1943 by Straumfjord for acne vulgaris. Since that time, retinoids have been utilized in the management and treatment of various skin conditions, including photoaging. Photodamage of the skin occurs as a consequence of cumulative exposure to solar ultraviolet radiation (UVR) and is characterized by deep wrinkles, easy bruising, inelasticity, mottled pigmentation, roughness, and telangiectasias. The mechanism of UVR-induced photodamage is multifactorial. Retinoids have demonstrated efficacy in the treatment of photoaged skin. Indeed, understanding the pathophysiology of photoaging and the molecular mechanism of retinoids can not only provide insight into the effects retinoids can exert in treating photoaging but also provide the rationale for their use in the treatment of other dermatologic diseases.

The antitumor effect of TIG3 in liver cancer cells is involved in ERK1/2 inhibition

Tazarotene-induced gene 3 (TIG3) was first characterized in tazarotene-treated human keratinocytes and identified as a retinoic acid responder gene, an important mediator of antitumor effects by retinoids. In this study, we aim to investigate the inhibitory effect of TIG3 on the growth of liver cancer and explore its underlying mechanism. Human hepatocellular carcinoma (HCC) Hep3B cells were transfected with plasmid GV141 carrying full-length TIG3 complementary DNA (cDNA). The effects of TIG3 on cell proliferation, apoptosis, and migration were determined in vitro. The suppressor effect of TIG3 on tumor growth was evaluated in vivo in a nude mouse HCC model. We observed that TIG3 expression is decreased in the Hep3B cell line as well as primary HCC tumors, and TIG3 expression inversely correlates with Ki-67 expression. Overexpression of TIG3 suppresses tumor growth in HCC both in vitro and in vivo via ERK1/2 inhibition by promoting apoptosis and inhibiting proliferation and migration. These findings identify TIG3 as an attractive therapeutic target for HCC.

TIG3: an important regulator of keratinocyte proliferation and survival

Tazarotene induced gene 3 (TIG3) is a tumor suppressor protein. In normal human epidermis, TIG3 is present in the differentiated, suprabasal layers and regulates terminal differentiation. TIG3 level is reduced in hyperproliferative diseases, including psoriasis and skin cancer, suggesting that loss of TIG3 is associated with enhanced cell proliferation. Moreover, transient expression of TIG3 leads to terminal differentiation in normal keratinocytes and apoptosis in skin cancer cells. In both cell types, TIG3 distributes to the cell membrane and to the centrosome. At the cell membrane, TIG3 interacts with and activates type I transglutaminase (TG1) to enhance keratinocyte terminal differentiation. TIG3 at the centrosome acts to inhibit centrosome separation during mitosis and to alter microtubule function. These findings argue that TIG3 is involved in control of keratinocyte differentiation and that loss of TIG3 in transformed cells contributes to the malignant phenotype.

Tazarotene: randomized, double-blind, vehicle-controlled, and open-label concurrent trials for basal cell carcinoma prevention and therapy in patients with basal cell nevus syndrome

Sporadic human basal cell carcinomas (BCC) are generally well managed with current surgical modalities. However, in the subset of high-risk patients predisposed to developing large numbers of BCCs, there is an unmet need for effective, low-morbidity chemoprevention. This population includes fair-skinned patients with extensive sun exposure and those with genodermatoses such as the basal cell nevus (Gorlin) syndrome (BCNS). Tazarotene (Tazorac, Allergan) is a topical retinoid with relative specificity for RAR-β and RAR-γ receptors. We previously demonstrated tazarotene's robust anti-BCC efficacy in Ptch1(+/-) mice, a murine equivalent of BCNS, and others have found it to have some efficacy against sporadic human BCCs. We report here results of a randomized, double-blind, vehicle-controlled study in patients with BCNS evaluating the efficacy of topically applied tazarotene for BCC chemoprevention (N = 34 subjects), along with an open-label trial evaluating tazarotene's efficacy for chemotherapy of BCC lesions (N = 36 subjects) for a maximum follow-up period of 3 years. We found that only 6% of patients had a chemopreventive response and that only 6% of treated BCC target lesions were clinically cured. Our studies provide no evidence for either chemopreventive or chemotherapeutic effect of tazarotene against BCCs in patients with BCNS.

Pericentrosomal localization of the TIG3 tumor suppressor requires an N-terminal hydrophilic region motif

Tazarotene-induced gene 3 (TIG3) is a tumor suppressor protein that has a key role in controlling cell proliferation. TIG3 is observed at reduced levels in epidermal squamous cell carcinoma, and the restoration of expression in skin cancer cells reduces cell survival. TIG3 suppresses cell survival through mechanisms that involve localization at the plasma membrane and at the centrosome. TIG3 interacts at the plasma membrane to activate enzymes involved in keratinocyte terminal differentiation, and at the centrosome to inhibit daughter centrosome separation during mitosis leading to cessation of cell proliferation and induction of apoptosis. An important goal is identifying the motifs required for TIG3 localization at these intracellular sites as a method to understand the function of TIG3 at each location. TIG3 encodes an N-terminal hydrophilic region (amino acids 1-135) and a C-terminal membrane-anchoring domain (amino acids 135-164). We show that the C-terminal hydrophobic domain targets intact TIG3 to the plasma membrane, but when isolated as an independent element localizes at the mitochondria. We further demonstrate that a segment of the N-terminal hydrophilic region targets the centrosome. These studies provide important insights regarding the mechanisms that guide subcellular localization of this keratinocyte survival regulator.

Expression of the class II tumor suppressor gene RIG1 is directly regulated by p53 tumor suppressor in cancer cell lines

Recent studies indicated that the RIG1 (RARRES3/TIG3) plays an important role in cell proliferation, differentiation, and apoptosis. However, the regulatory mechanism of RIG1 gene expression has not been clearly elucidated. In this study, we identified a functional p53 response element (p53RE) in the RIG1 gene promoter. Transfection studies revealed that the RIG1 promoter activity was greatly enhanced by wild type but not mutated p53 protein. Sequence specific mutation of the p53RE abolished p53-mediated transactivation. Specific binding of p53 protein to the rig-p53RE was demonstrated using electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) assay. Further studies confirmed that the expression of RIG1 mRNA and protein is enhanced through increased p53 protein in HepG2 or in H24-H1299 cells. In conclusion, our results indicated that RIG1 gene is a downstream target of p53 in cancer cell lines.

TIG3 interaction at the centrosome alters microtubule distribution and centrosome function

TIG3 is an important pro-differentiation regulator that is expressed in the suprabasal epidermis. We have shown that TIG3 activates selective keratinocyte differentiation-associated processes leading to cornified envelope formation. However, TIG3 also suppresses cell proliferation by an unknown mechanism. Our present studies suggest that cessation of growth is mediated through the impact of TIG3 on the centrosome and microtubules. The centrosome regulates microtubule function in interphase cells and microtubule spindle formation in mitotic cells. We show that TIG3 colocalizes with γ-tubulin and pericentrin at the centrosome. Localization of TIG3 at the centrosome alters microtubule nucleation and reduces anterograde microtubule growth, increases acetylation and detyrosination of α-tubulin, increases insoluble tubulin and drives the formation of a peripheral microtubule ring adjacent to the plasma membrane. In addition, TIG3 suppresses centrosome separation, but not duplication, and reduces cell proliferation. We propose that TIG3 regulates the formation of the peripheral microtubule ring observed in keratinocytes of differentiated epidermis and also has a role in the cessation of proliferation in these cells.

TIG3 tumor suppressor-dependent organelle redistribution and apoptosis in skin cancer cells

TIG3 is a tumor suppressor protein that limits keratinocyte survival during normal differentiation. It is also important in cancer, as TIG3 level is reduced in tumors and in skin cancer cell lines, suggesting that loss of expression may be required for cancer cell survival. An important goal is identifying how TIG3 limits cell survival. In the present study we show that TIG3 expression in epidermal squamous cell carcinoma SCC-13 cells reduces cell proliferation and promotes morphological and biochemical apoptosis. To identify the mechanism that drives these changes, we demonstrate that TIG3 localizes near the centrosome and that pericentrosomal accumulation of TIG3 alters microtubule and microfilament organization and organelle distribution. Organelle accumulation at the centrosome is a hallmark of apoptosis and we demonstrate that TIG3 promotes pericentrosomal organelle accumulation. These changes are associated with reduced cyclin D1, cyclin E and cyclin A, and increased p21 level. In addition, Bax level is increased and Bcl-XL level is reduced, and cleavage of procaspase 3, procaspase 9 and PARP is enhanced. We propose that pericentrosomal localization of TIG3 is a key event that results in microtubule and microfilament redistribution and pericentrosomal organelle clustering and that leads to cancer cell apoptosis.

Primary and metastatic malignant tumors of the scalp: an update

In recent years there have been a number of interesting advances in several topics relating to the diagnosis and treatment of cutaneous lesions with particular applicability to primary and metastatic malignancies of the scalp. In this article we provide a general update of advances in this field, and cover the more salient points relating to a variety of malignant tumors that have been reported to appear on the scalp as primary or metastatic lesions. A search and review of the literature on PubMed was made to identify and discuss relevant points relating to diagnosis and treatment of primary and metastatic tumors of the scalp. We describe the anatomy of the scalp, epidemiology of scalp tumors, theories of field cancerization and field therapy, photodynamic therapy, excisional surgical techniques and reconstruction, lymphoscintigraphy, chemoprevention, as well as details relating to atypical fibroxanthoma, Brooke-Spiegler syndrome, nevus sebaceus, cutaneous lymphoma, and metastatic disease. There is a very broad differential diagnosis for scalp nodules, which includes many different benign and malignant diseases, and treatment should be tailored accordingly. Given the potential for poor prognosis with some of the more aggressive malignancies that can be found in this anatomic area, the importance of a thorough physical examination cannot be emphasized enough, and early detection is critical to provide patients with the best chance for a favorable outcome.

TIG3: a regulator of type I transglutaminase activity in epidermis

Keratinocytes undergo a process of terminal cell differentiation that results in the construction of a multilayered epithelium designed to produce a structure that functions to protect the body from dehydration, abrasion and infection. These protective properties are due to the production of a crosslinked layer of protein called the cornified envelope. Type I transglutaminase (TG1), an enzyme that catalyzes the formation of epsilon-(gamma-glutamyl)lysine bonds, is the key protein responsible for generation of the crosslinks. The mechanisms that lead to activation of transglutaminase during terminal differentiation are not well understood. We have identified a protein that interacts with TG1 and regulates its activity. This protein, tazarotene-induced gene 3 (TIG3), is expressed in the differentiated layers of the epidermis and its expression is associated with transglutaminase activation and cornified envelope formation. We describe a novel mechanism whereby TIG3 regulates TG1 activity.

Induction of apoptosis by the retinoid inducible growth regulator RIG1 depends on the NC motif in HtTA cervical cancer cells

Background

Retinoid-inducible gene 1 (RIG1), also known as tazarotene-induced gene 3 or retinoic-acid receptor responder 3, is a growth regulator, which induces apoptosis and differentiation. RIG1 is classified into the NC protein family. This study investigated functional domains and critical amino acids associated with RIG1-mediated cell death and apoptosis.

Results

Using enhanced green fluorescence protein (EGFP)-tagged RIG1 variants, RIG1 proteins with deletion at the NC domain significantly decreased cell death induced by RIG1, and fusion variants containing only the NC domain significantly induced apoptosis of HtTA cervical cancer cells. The EGFP-RIG1-induced apoptosis was significantly decreased in cells expressing N¹¹²C¹¹³ motif double- (NC→FG) or triple- (NCR→FGE) mutated RIG1 variants. Using dodecapeptides, nuclear localization and profound cell death was observed in HtTA cells expressing wild type RIG1_111–123 or Leu¹²¹-mutated RIG1_111–123:L→ C peptide, but peptides double- or triple-mutated at the NC motif alone, RIG1_111–123:NC→FG or RIG1_111–123:NCR→FGE, were cytoplasmically localized and did not induce apoptosis. The RIG1_111–123 also induced apoptosis of A2058 melanoma cells but not normal human fibroblasts.

Conclusion

The NC domain, especially the NC motif, plays the major role in RIG1-mediated pro-apoptotic activity. The RIG1_111–123 dodecapeptide exhibited strong pro-apoptotic activity and has potential as an anticancer drug.

Effects of narrow-band ultraviolet B and tazarotene therapy on keratinocyte proliferation and TIG3 expression

Tazarotene plus narrow-band ultraviolet B (NB-UVB) therapy has been shown to enhance the efficacy in treating patients with psoriasis, while the mechanism is not clear. The present study aims to investigate the alteration of cell proliferation and TIG3 in cultured normal human keratinocytes after NB-UVB and/or tazarotene treatment. Keratinocytes were exposed to NB-UVB, then incubated with or without tazarotene, and then cell proliferation was detected by methyl thiazoleterazolium colorimetric assay and TIG3 mRNA expression and protein production was examined by real-time reverse transcription polymerase chain reaction and immunocytochemistry, respectively. The results show that keratinocyte proliferation was inhibited and TIG3 mRNA expression and protein production were elevated by tazarotene at a dose higher than 0.1 micromol/L. In NB-UVB single irradiating groups, only 200 mJ/cm2 NB-UVB inhibited keratinocyte proliferation, and none of the irradiated groups had an effect on TIG3 expression. Moreover, tazarotene plus NB-UVB have stronger effects than those separately. These results indicate NB-UVB plus tazarotene may have synergistic effects on inhibiting keratinocyte proliferation and elevating TIG3 expression, which may have some implications for the understanding of how to treat psoriasis patients with tazarotene plus NB-UVB.

Basal cell carcinomas: attack of the hedgehog

Basal cell carcinomas (BCCs) were essentially a molecular 'black box' until some 12 years ago, when identification of a genetic flaw in a rare subset of patients who have a great propensity to develop BCCs pointed to aberrant Hedgehog signalling as the pivotal defect leading to formation of these tumours. This discovery has facilitated a remarkable increase in our understanding of BCC carcinogenesis and has highlighted the carcinogenic role of this developmental pathway when aberrantly activated in adulthood. Importantly, a phase 1 first-in-human trial of a Hedgehog inhibitor has shown real progress in halting and even reversing the growth of these tumours.

Localization of the TIG3 transglutaminase interaction domain and demonstration that the amino-terminal region is required for TIG3 function as a keratinocyte differentiation regulator

Tazarotene-induced gene 3 (TIG3) regulates keratinocyte terminal differentiation by activating type I transglutaminase (TG1). TIG3 consists of an amino-terminal (N-terminal) segment, that encodes several conserved motifs, and a carboxy-terminal (C-terminal) membrane-anchoring domain. By producing a series of truncation mutants that remove segments of the N-terminal region, and monitoring the ability of each mutant to co-precipitate TG1, function as a TG1 substrate, or functionally localize with TG1 in cells, we show that the TIG3 domain that interacts with TG1 is located within a TIG3 segment spanning amino acids 112-164. Although they bind TG1, TIG3 mutants lacking the conserved N-terminal region drive apoptosis-like cell death characterized by cell rounding, membrane blebbing, cytochrome c release, procaspase-3 and poly(ADP-ribose)polymerase (PARP) cleavage, and reduced p53 and p21 levels. Compared with TIG3, these truncated mutants have an increased tendency to associate with membranes. A mutant lacking the C-terminal membrane-anchoring domain is inactive. These findings suggest that TIG3 interaction with TG1 does not require the N-terminal conserved domains, that the TIG3 N-terminal region is required for TIG3-dependent keratinocyte differentiation, that its removal converts TIG3 into a proapoptotic protein, and that this change in action of TIG3 is associated with an intracellular redistribution.

Mechanisms of the HRSL3 tumor suppressor function in ovarian carcinoma cells

HRSL3 (also known as H-REV107-1) belongs to a class II tumor suppressor gene family and is downregulated in several human tumors including ovarian carcinomas. To unravel the mechanism of HRSL3 tumor suppressor action, we performed a yeast two-hybrid screen and identified the alpha-isoform of the regulatory subunit A of protein phosphatase 2A (PR65alpha) as a new interaction partner of HRSL3. Interaction between HRSL3 and PR65alpha was confirmed in vitro and by co-immunoprecipitation in mammalian cells. We demonstrate that HRSL3 binds to the endogenous PR65alpha, thereby partially sequestering the catalytic subunit PR36 from the PR65 protein complex, and inhibiting PP2A catalytic activity. Furthermore, binding of HRSL3 to PR65 induces apoptosis in ovarian carcinoma cells in a caspase-dependent manner. Using several mutant HRSL3 constructs, we identified the N-terminal proline-rich region within the HRSL3 protein as the domain that is relevant for both binding of PR65alpha and induction of programmed cell death. This suggests that the negative impact of HRSL3 onto PP2A activity is important for the HRSL3 pro-apoptotic function and indicates a role of PP2A in survival of human ovarian carcinomas. The analysis of distinct PP2A target molecules revealed PKCzeta as being involved in HRSL3 action. These data implicate HRSL3 as a signaling regulatory molecule, which is functionally involved in the oncogenic network mediating growth and survival of ovarian cancer cells.

RIG1 inhibits the Ras/mitogen-activated protein kinase pathway by suppressing the activation of Ras

The retinoid-inducible gene 1 (RIG1) protein is a retinoid-inducible growth regulator. Previous studies have shown that the RIG1 protein inhibits the signaling pathways of Ras/mitogen-activated protein kinases. However, neither the mode of action nor the site of inhibition of RIG1 is known. This study investigated the effects of RIG1, and the mechanisms responsible for these effects, on the activation of Ras proteins in HtTA cervical cancer cells. RIG1 reduced the levels of activated Ras (Ras-GTP) and total Ras protein in cells transfected with mutated H-, N-, or K-Ras(G12V), or in cells transfected with the wild type H- or N-Ras followed by stimulation with epidermal growth factor. The half-life of Ras protein decreased from more than 36 h in control cells to 18 h in RIG1-transfected cells. RIG1 immunoprecipitated with the Ras protein in co-transfected cellular lysates. In contrast to the predominant plasma membrane localization in control cells, the H-Ras fusion protein EGFP-H-Ras was localized within a discrete cytoplasmic compartment where it co-localized with RIG1. RIG1 inhibited more than 93% of the Elk- and CHOP-mediated transactivation induced by H- or K-Ras(G12V). However, RIG1 did not inhibit the transactivation induced by MEK1 or MEK3, and failed to suppress the phosphorylation of extracellular signal-regulated kinases 1 and 2 induced by the constitutively activated B-Raf(V599E). The RIG1 with carboxyl terminal truncation (RIG1DeltaC) did not immunoprecipitate with Ras and had no effect on Ras activation or transactivation of the downstream signal pathways. These data indicate that RIG1 exerts its inhibitory effect at the level of Ras activation, which is independent of Ras subtype but dependent on the membrane localization of the RIG1 protein. This inhibition of Ras activation may be mediated through downregulation of Ras levels and alteration of Ras subcellular distribution.

RARRES1 expression is significantly related to tumour differentiation and staging in colorectal adenocarcinoma

Retinoic acid receptor responder 1 (RARRES1) is a retinoid regulated gene. Its expression is frequently down-regulated through DNA hypermethylation in several types of malignant tissues. This study investigated the clinical significance of RARRES1 protein and its association with RARRES3 protein expression in 161 (26 adenoma, 13 distal normal mucosa and 122 primary colorectal adenocarcinoma) paraffin-embedded colorectal tissues by immunohistochemistry. RARRES1 protein was detected at the highest levels in terminally differentiated cells of normal mucosal tissues and all 26 adenoma tissues. Among 122 colorectal adenocarcinomas, the poorly differentiated adenocarcinomas and Dukes' stage D tumours showed a significant decrease in RARRES1 expression (P < 0.001 and P < 0.01, respectively). RARRES1 expression was significantly (P < 0.001) correlated with RARRES3 expression, which was positively associated with tumour differentiation (P < 0.001). Difference in expression of RARRES1 among 119 patients had no apparent effect on patient survival. Our results suggest the role of RARRES1 in colorectal epithelial differentiation, and the down-regulation of RARRES1 is related to stage D progression.

Identification and characterization of the retinoic acid response elements in the human RIG1 gene promoter

The expression of retinoic acid-induced gene 1 (RIG1), a class II tumor suppressor gene, is induced in cells treated with retinoids. RIG1 has been shown to express ubiquitously and the increased expression of this gene appears to suppress cell proliferation. Recent studies also demonstrated that this gene may play an important role in cell differentiation and the progression of cancer. In spite of the remarkable regulatory role of this protein, the molecular mechanism of RIG1 expression induced by retinoids remains to be clarified. The present study was designed to study the molecular mechanism underlying the all-trans retinoic acid (atRA)-mediated induction of RIG1 gene expression. Polymerase chain reaction was used to generate a total of 10 luciferase constructs that contain various fragments of the RIG1 5'-genomic region. These constructs were then transfected into human gastric cancer SC-M1 and breast cancer T47D cells for transactivation analysis. atRA exhibited a significant induction in luciferase activity only through the -4910/-5509 fragment of the 5'-genomic region of RIG1 gene relative to the translation initiation site. Further analysis of this promoter fragment indicated that the primary atRA response region is located in between -5048 and -5403 of the RIG1 gene. Within this region, a direct repeat sequence with five nucleotide spacing, 5'-TGACCTctattTGCCCT-3' (DR5, -5243/-5259), and an inverted repeat sequence with six nucleotide spacing, 5'-AGGCCAtggtaaTGGCCT-3' (IR6, -5323/-5340), were identified. Deletion and mutation of the DR5, but not the IR6 element, abolished the atRA-mediated activity. Electrophoretic mobility shift assays with nuclear extract from atRA-treated cells indicated the binding of retinoic acid receptor (RAR) and retinoid X receptor (RXR) heterodimers specifically to this response element. In addition to the functional DR5, the region contains many other potential sequence elements that are required to maximize the atRA-mediated induction. Taken together, we have identified and characterized the functional atRA response element that is responsible for the atRA-mediated induction of RIG1 gene.

Decreased expression of type II tumor suppressor gene RARRES3 in tissues of hepatocellular carcinoma and cholangiocarcinoma

AIM: To analyze the expression of retinoic acid receptor responder 3 (RARRES3) protein in paraffin-embedded tissues of hepatocellular carcinoma (HCC) and cholangiocarcinoma (CC), and the correlation of RARRES3 production with tumor differentiation.

METHODS: Expression of RARRES3 in tissues from 21 CC (10 well-, 7 moderately- and 4 poorly-differentiated) and 32 HCC was determined by immunohistochemistry.

RESULTS: Among 21 CC tissues, RARRES3 was detected in 8 (80%) of 10 well-differentiated tumors. Only 2 (18.2%) out of 11 tumors with moderate or poor differentiation showed positive RARRES3 expression. RARRES3 expression in well-differentiated CC was significantly higher than that in tumors with moderate or poor differentiation (Fisher exact test, P<0.01). Expression of RARRES3 was not different between early (I and II) and late (III and IV) stages of CC. Among 30 HCC tissues, 17 (56.7%) weakly expressed RARRES3 in HCC cells, and 25 (83.3%) normal tissues adjacent to HCC expressed the protein. RARRES3 expression was significantly decreased in HCC tissues compared to that in adjacent normal tissues (logistic regression analysis, OR = 0.27, 95% CI (0.11-0.62), P<0.01).

CONCLUSION: Expression of RARRES3 is positively correlated to well-differentiated CC, which supports the role of RARRES3 in malignant epithelial differentiation of the tumor. The decrease in RARRES3 expression in tissues of HCC and CC with moderate and poor differentiation suggests that altered RARRES3 expression may play a role in the carcinogenesis of the liver and biliary tract.

Suppression of theTIG3 tumor suppressor gene in human ovarian carcinomas is mediatedvia mitogen-activated kinase-dependent and -independent mechanisms

The TIG3 gene is a retinoic acid inducible class II tumor suppressor gene downregulated in several human tumors and malignant cell lines. Diminished TIG3 expression correlates with decreased differentiation whereas forced expression of TIG3 suppresses oncogenic signaling pathways and subsequently induces differentiation or apoptosis in tumor cells. Analysis of TIG3 mRNA expression in a large set of cDNA pools derived from matched tumor and normal human tissues showed a significant downregulation of TIG3 in 29% of the cDNA samples obtained from ovarian carcinomas. Using in situ hybridization, we demonstrated expression of TIG3 in the epithelial lining of 7 normal ovaries but loss of TIG3 expression in 15/19 of human ovarian carcinoma tissues. In SKOV-3, CAOV-3 and ES-2 ovarian carcinoma cell lines, downregulation of TIG3 mRNA was reversible and dependent on an activated MEK-ERK signaling pathway. Re-expression of TIG3 mRNA in these cells upon specific interference with the MEK-pathway was correlated with growth inhibition of the cells. In OVCAR-3 and A27/80 ovarian carcinoma cells, TIG3 suppression is MEK-ERK independent, but expression could be reconstituted upon interferon gamma (IFNgamma) induction. Overexpression of TIG3 in A27/80 ovarian carcinoma cells significantly impaired cell growth and despite increased mRNA levels, TIG3 protein was hardly detectable. These results suggest that TIG3 is negatively regulated by an activated MEK-ERK signaling pathway. Further mechanisms must interfere with TIG3 expression that are independent of MEK and partially include interferon-responsive components.

Topical Tazarotene Chemoprevention Reduces Basal Cell Carcinoma Number and Size in Ptch1+/− Mice Exposed to Ultraviolet or Ionizing Radiation

Oral retinoids can reduce basal cell carcinoma (BCC) incidence in genetically susceptible patients, and one topical retinoid, tazarotene, has been reported to cure some sporadic BCCs. Therefore, we have tested whether this agent would affect BCCs in Ptch1+/- mice in a controlled chemoprevention trial. We found that topical tazarotene dramatically inhibits the formation of BCCs induced with either UV or ionizing radiation. The ability of tazarotene to inhibit BCC formation in this mouse model provides encouragement for the use of tazarotene in skin cancer chemoprevention trials in humans.

Tazarotene 0.1% gel for refractory mycosis fungoides lesions: an open-label pilot study

BACKGROUND

Topical skin-directed therapies are used to induce remissions in early-stage mycosis fungoides (MF). They are rarely curative, and responding patients are subject to frequent relapses, emphasizing the need for alternative therapies.

OBJECTIVE

We sought to evaluate the efficacy and tolerability of topical tazarotene 0.1% gel as adjuvant therapy in the treatment of refractory MF lesions.

METHODS

A total of 20 adult patients with early patch or plaque MF limited to less than 20% body surface area (BSA) involvement whose lesions were either stable or refractory to therapy for at least 8 weeks enrolled in an open-label pilot study. Tazarotene 0.1% gel was applied to MF lesions once daily for 24 weeks. Continued concomitant use of other medications such as low- to mid-potency topical corticosteroids was permitted for the alleviation of skin irritation. Global improvement, overall disease severity, percent BSA involvement, and pruritus were evaluated every 4 weeks. Up to 6 index lesions were followed up for area, plaque elevation, scaling, and erythema scores. Skin biopsy specimens were to be taken at baseline, week 8, and week 24. Evaluable specimens were stained with hematoxylin and eosin, CD8 antibody, and CD45RO antibody.

RESULTS

In all, 20 patients enrolled, 19 received treatment, and 16 completed at least 4 weeks of topical treatment. By intent-to-treat analysis, 11 of 19 patients (58%) achieved at least a moderate (>50%) global improvement in BSA, and 35% of 99 index lesions cleared completely. Significant reductions (mean differences) were also found in the median lesional area score (-37, P =.0013), mean plaque elevation score (-.67, P =.016), mean scaling (-0.70, P =.033), and mean erythema score (-1.03, P =.002). Analysis of overall disease also disclosed statistical differences in percent of change for BSA involvement of 22% (P =.013) and of mean overall disease severity score of 34% (P =.011). Of 19 patients, 16 (84%) experienced mild or moderate local skin irritation manifested by peeling, erythema, burning, and tenderness that was managed successfully with topical steroids or reducing the frequency of treatment. Histopathology and immunohistochemistry results showed reductions in lymphocytic infiltrates and percentage of CD45RO(+) lymphocytes, and increases in the percentage of CD8(+) lymphocytes during the course of therapy.

CONCLUSION

In this small pilot study, tazarotene 0.1% gel was a well-tolerated and effective adjuvant topical for the treatment of refractory MF lesions by clinical and histologic assessments.