Tazarotene-induced Gene 1 Expression Research Articles

Tazarotene-induced Gene 1 Induces Melanoma Cell Death by Triggering Endoplasmic Reticulum Stress Response.

This study investigated the mechanism by which tazarotene-induced gene 1 (TIG1) inhibits melanoma cell growth. The main focus was to analyze downstream genes regulated by TIG1 in melanoma cells and its impact on cell growth. The effects of TIG1 expression on cell viability and death were assessed using water-soluble tetrazolium 1 (WST-1) mitochondrial staining and lactate dehydrogenase release assays. RNA sequencing and Western blot analysis were employed to investigate the genes regulated by TIG1 in melanoma cells. Additionally, the correlation between TIG1 expression and its downstream genes was analyzed in a melanoma tissue array. TIG1 expression in melanoma cells was associated with decreased cell viability and increased cell death. RNA-sequencing (RNA-seq), quantitative reverse transcription PCR (reverse RT-QPCR), and immunoblots revealed that TIG1 expression induced the expression of Endoplasmic Reticulum (ER) stress response-related genes such as Homocysteine-responsive endoplasmic reticulum-resident ubiquitin-like domain member 1 (HERPUD1), Binding immunoglobulin protein (BIP), and DNA damage-inducible transcript 3 (DDIT3). Furthermore, analysis of the melanoma tissue array revealed a positive correlation between TIG1 expression and the expression of HERPUD1, BIP, and DDIT3. Additionally, attenuation of the ER stress response in melanoma cells weakened the impact of TIG1 on cell growth. TIG1 expression effectively hinders the growth of melanoma cells. TIG1 induces the upregulation of ER stress response-related genes, leading to an increase in caspase-3 activity and subsequent cell death. These findings suggest that the ability of retinoic acid to prevent melanoma formation may be associated with the anticancer effect of TIG1.

Tazarotene-induced gene 1 interacts with Polo-like kinase 2 and inhibits cell proliferation in HCT116 colorectal cancer cells.

Tazarotene-induced gene 1 (TIG1) is considered to be a tumor suppressor gene that is highly expressed in normal or well-differentiated colon tissues, while downregulation of TIG1 expression occurs in poorly differentiated colorectal cancer (CRC) tissues. However, it is still unclear how TIG1 regulates the tumorigenesis of CRC. Polo-like kinases (Plks) are believed to play an important role in regulating the cell cycle. The performance of PLK2 in CRC is negatively correlated with the differentiation status of CRC tissues. Here, we found that PLK2 can induce the growth of CRC cells and that TIG1 can prevent PLK2 from promoting the proliferation of CRC cells. We also found that the expression of PLK2 in CRC cells was associated with low levels of Fbxw7 protein and increased expression of cyclin E1. When TIG1 was coexpressed with PLK2, the changes in Fbxw7/cyclin E1 levels induced by PLK2 were reversed. In contrast, silencing TIG1 promoted the proliferation of CRC, and when PLK2 was also silenced, the proliferation of CRC cells induced by TIG1 silencing was significantly inhibited. The above research results suggest that TIG1 can regulate the tumorigenesis of CRC by regulating the activity of PLK2.

Cathepsin V Mediates the Tazarotene-induced Gene 1-induced Reduction in Invasion in Colorectal Cancer Cells.

Tazarotene-induced gene 1 (TIG1) is a retinoid acid receptor-responsive gene involved in cell differentiation and tumorigenesis. Aberrant methylation of CpG islands in the TIG1 promoter is found in multiple cancers. Currently, the exact mechanism underlying the anticancer effect of TIG1 is unknown. Here, we show that TIG1 interacts with cathepsin V (CTSV), which reduces CTSV stability and subsequently affects the production of activated urokinase-type plasminogen activator (uPA), an epithelial-mesenchymal transition-associated protein. Ectopic expression of CTSV increased the expression of activated uPA and the number of migrated and invaded cells, whereas ectopic TIG1 expression reversed the effects of CTSV on the uPA signaling pathway. Similar patterns in the production of activated uPA and number of migrated and invaded cells were also observed in TIG1-expressing and CTSV-knockdown cells. The results suggest that CTSV may participate in TIG1-regulated uPA activity and the associated downstream signaling pathway.

Tazarotene-Induced Gene 1 (TIG1) Interacts with Serine Protease Inhibitor Kazal-Type 2 (SPINK2) to Inhibit Cellular Invasion of Testicular Carcinoma Cells.

Tazarotene-induced gene 1 (TIG1) encodes a protein that is a retinoid-regulated tumor suppressor. TIG1 is expressed in most normal tissues, and downregulation of TIG1 expression in multiple cancers is caused by promoter hypermethylation. Kazal-type serine protease inhibitor-2 (SPINK2) is a serine protease inhibitor, and the SPINK protein family has been shown to inhibit the expression of urokinase-type plasminogen activator (uPA). In addition, increased levels of uPA and the uPA receptor were observed in testicular cancer tissues. This study demonstrated that TIG1 interacts with SPINK2 in NT2/D1 testicular carcinoma cells. TIG1 and SPINK2 were highly expressed in normal testis tissues, while low expression levels of TIG1 and SPINK2 were found in testicular cancer tissues. TIG1 inhibited cell invasion, migration, and epithelial–mesenchymal transition (EMT) of NT2/D1 cells. SPINK2 enhanced TIG1-regulated uPA activity and EMT suppression, while silencing SPINK2 alleviated TIG1-mediated EMT regulation, cell migration, and invasion. Therefore, the results suggest that the interaction between TIG1 and SPINK2 plays an important role in the inhibition of testicular cancer cell EMT, and suppression is mediated through downregulation of the uPA/uPAR signaling pathway.

Tazarotene-Induced Gene 1 Enhanced Cervical Cell Autophagy through Transmembrane Protein 192.

Tazarotene-induced gene 1 (TIG1) is a retinoic acid-inducible protein that is considered a putative tumor suppressor. The expression of TIG1 is decreased in malignant prostate carcinoma or poorly differentiated colorectal adenocarcinoma, but TIG1 is present in benign or well-differentiated tumors. Ectopic TIG1 expression led to suppression of growth in cancer cells. However, the function of TIG1 in cell differentiation is still unknown. Using a yeast two-hybrid system, we found that transmembrane protein 192 (TMEM192) interacted with TIG1. We also found that both TIG1A and TIG1B isoforms interacted and co-localized with TMEM192 in HtTA cervical cancer cells. The expression of TIG1 induced the expression of autophagy-related proteins, including Beclin-1 and LC-3B. The silencing of TMEM192 reduced the TIG1-mediated upregulation of autophagic activity. Furthermore, silencing of either TIG1 or TMEM192 led to alleviation of the upregulation of autophagy induced by all-trans retinoic acid. Our results demonstrate that the expression of TIG1 leads to cell autophagy through TMEM192. Our study also suggests that TIG1 and TMEM192 play an important role in the all-trans retinoic acid-mediated upregulation of autophagic activity.

Aberrant TIG1 methylation associated with its decreased expression and clinicopathological significance in hepatocellular carcinoma

Recently, it has been reported that tazarotene-induced gene 1 (TIG1) methylation was frequently detected in a variety of human cancers. However, the relationship between the TIG1 methylation and the characteristics of hepatocellular carcinoma (HCC) remains unknown. The aim of present study was to observe the promoter methylation of TIG1 in HCC tissues and assess its prognostic significance for HCC. Real-time quantitative polymerase chain reaction and methylation-specific polymerase chain reaction were used, respectively, to examine the mRNA expression and methylation status of TIG1 in 91 pairs of HCC and adjacent noncancerous tissues. The mRNA expression level of TIG1 was significantly lower in HCC tissues than in adjacent noncancerous tissues. The rate of TIG1 promoter methylation was significantly higher in HCC tissues than in adjacent noncancerous tissues (P < 0.001). A strong correlation between downregulation and promoter methylation was found in these tumors (P < 0.001). More importantly, TIG1 methylation status was related to tumor size (P = 0.015), histological differentiation (P = 0.004), and tumor stage (P < 0.001). Kaplan-Meier survival analysis showed that TIG1 promoter hypermethylation was associated with a worse outcome in patients with HCC. Further, Cox multivariate analysis indicated that TIG1 methylation status was an independent prognostic factor for the overall survival rate of HCC patients. In conclusion, our data suggested that epigenetic silencing of TIG1 gene expression by promoter hypermethylation may play an important role in HCC.

Abstract 3032: Tazarotene-induced gene 1 promotes tumorigenicity and invasiveness of inflammatory breast cancer through receptor tyrosine kinase Axl.

Abstract Inflammatory breast cancer (IBC) is the most lethal and aggressive form of breast cancer and is highly metastatic. The prognosis of patients with IBC is poor, and effective standard therapies for IBC are limited because the molecular mechanisms underlying the pathogenesis of IBC remain unknown. Therefore, there is an urgent need to identify novel molecules that are responsible for the aggressiveness of IBC and to elucidate the molecular mechanisms involved in tumorigenesis and metastasis of IBC. Such work may lead to early IBC diagnosis and new targeted therapies for IBC. We recently found that tazarotene-induced gene 1 (TIG1) expression is significantly higher in IBC cell lines than in non-IBC cell lines. In both IBC and non-IBC data sets, estrogen receptor-negative/HER2-negative samples had significantly higher expression of TIG1 than did other clinical subtypes (estrogen receptor-positive/HER2-negative and HER2-positive). Therefore, we hypothesized that TIG1 plays an important role in the malignant process of IBC. In these studies, we determined the biological function of TIG1 in IBC cells and elucidated the molecular mechanism by which TIG1 regulates the invasiveness of IBC cells. Our data show that high expression of TIG1 significantly correlated with shorter survival of patients with IBC . Knockdown of TIG1 expression in IBC cells reduced their proliferation, migration, and invasion in vitro. Also, silencing of TIG1 dramatically inhibited IBC tumor growth in a xenograft model. Moreover, restoring TIG1 expression rescued the proliferation, motility, and invasiveness of TIG1-silenced IBC cells. Most importantly, we identified Axl as a functional partner of TIG1 by showing that Axl expression positively correlated with TIG1 expression in IBC human tissues and TIG1 interacted with and stabilized Axl in IBC cells. TIG1 regulated the invasiveness of IBC cells through mediation of the Axl signaling pathway. In SUM149 cells, TIG1 depletion decreased Axl expression, which led to downregulation of expression of matrix metalloproteinase-9, a molecule required for Axl-mediated invasion, and inactivation of nuclear factor-κB, ultimately leading to decreased invasiveness of IBC cells. In summary, our results identified TIG1 as an oncogenic gene that contributes to the tumorigenic and metastatic properties of IBC. Our data also linked TIG1 with the key tumorigenic gene Axl in IBC cells. Further studies are needed to confirm that TIG1 is a promising IBC-specific therapeutic target in the treatment of patients with IBC. Citation Format: Xiaoping Wang, Hitomi Saso, Takayuki Iwamoto, Weiya Xia, Yun Gong, Lajos Pusztai, Wendy Woodward, James M. Reuben, Gabriel N. Hortobagyi, Mien-Chie Hung, Naoto T. Ueno. Tazarotene-induced gene 1 promotes tumorigenicity and invasiveness of inflammatory breast cancer through receptor tyrosine kinase Axl. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3032. doi:10.1158/1538-7445.AM2013-3032

P2-02-01: A Novel Inflammatory Breast Cancer-Specific Oncogene, Tazarotene-Induced Gene 1, Promotes Tumorigenicity and Invasiveness through the Receptor Tyrosine Kinase Axl.

Abstract Background: Inflammatory breast cancer (IBC) is the most lethal and aggressive form of breast cancer and is highly metastatic. The prognosis of patients with IBC is poor, and effective standard therapies for IBC are limited because the molecular mechanisms underlying the pathogenesis of IBC remain unknown. We recently found that tazarotene-induced gene 1 (TIG1) expression is significantly higher in IBC cell lines than in non-IBC cell lines. In both IBC and non-IBC data sets, estrogen receptor-negative/HER2−negative samples had significantly higher expression of TIG1 than did other clinical subtypes (estrogen receptor-positive/HER2−negative and HER2−positive). Therefore, we hypothesized that TIG1 plays an important role in the malignant process of IBC. In these studies, we determined the biological function of TIG1 in IBC cells and elucidated the molecular mechanism by which TIG1 regulates the invasiveness of IBC cells. Methods: TIG1 expression in SUM149 and KPL-4 IBC cells was stably knocked down, and the effects of this knockdown on in vitro cell proliferation, migration, and invasion were analyzed. The effects of restoring TIG1 expression on TIG1-silencing IBC cells were also examined. To determine the tumorigenic activity of TIG1 in vivo, TIG1 stable-knockdown SUM149 cells and control shRNA-transfected cells were implanted into the mammary fat pads of athymic nude mice, and tumor growth was monitored. The receptor tyrosine kinase Axl, a potential functional partner of TIG1, was identified using DNA microarray analysis. The interaction between TIG1 and Axl in IBC cells was examined using immunoprecipitation and confocal microscopy assays. The signaling pathway in IBC cells in which TIG1 participates was also investigated. Results: Knockdown of TIG1 expression in IBC cells reduced their proliferation, migration, and invasion in vitro. Also, silencing of TIG1 dramatically inhibited IBC tumor growth in a xenograft model. Moreover, restoring TIG1 expression rescued the proliferation, motility, and invasiveness of TIG1-silenced IBC cells. Most importantly, we identified Axl as a functional partner of TIG1 by showing that TIG1 interacted with and stabilized Axl in IBC cells. TIG1 regulated the invasiveness of IBC cells through mediation of the Axl signaling pathway. In SUM149 cells, TIG1 depletion decreased Axl expression, which led to downregulation of expression of matrix metalloproteinase-9, a molecule required for Axl-mediated invasion, and inactivation of nuclear factor-kB, ultimately leading to decreased invasiveness of IBC cells. Conclusion: Our results identified TIG1 as an oncogenic gene that contributes to the tumorigenic and metastatic properties of IBC. Our data also linked TIG1 with the key tumorigenic gene Axl in IBC cells. Further studies designed to establish TIG1 as a therapeutic target in the treatment of patients with IBC are under way. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-02-01.

Expression and Mutation Analysis of TIG1 (Tazarotene-Induced Gene 1) in Human Gastric Cancer

Tazarotene-induced gene 1 (TIG1) has been known to function as a cell adhesion molecule, which leads to better cell to cell contact and reduced proliferation. We investigated expression and mutation status of TIG1 in primary gastric tumors and cell lines to explore the candidacy of the gene as a tumor suppressor. A total of 172 gastric tissue specimes, including 80 primary adenocarcinomas, 12 benign tumors, and 80 adjacent normal mucosa, and 15 gastric cancer cell lines were used. TIG1 expression was analyzed by semiquantitative RT-PCR and immunoblot analysis. To screen for the presence of somatic mutations, RT-PCR-SSCP analysis was carried out. The effect of 5-aza-2'-deoxycytidine treatment was examined to elicit whether TIG1 reduction is associated with abnormal DNA hypermethylation. Compared to noncancerous tissues, a substantial reduction of TIG1 expression was observed in 73.3% (11115) cancer cell lines, and seven of these exhibited nearly undetectable levels of expression. Decreased expression of TIG1 was also found in 62 (77.5%) primary carcinoma tissues compared to adjacent noncancerous tissues, indicating a tumor-specific reduction of TIG1. Expression levels of TIG1 were significantly low in primary carcinomas and cancer cell lines compared to those of normal tissues. Moreover, loss or reduction of TIG1 was significantly high in advanced tumors compared to early tumors and more frequent in poorly differentiated tumors than well or moderately differentiated tumors. TIG1 expression was reactivated or its level was elevated following 5-aza-2'-deoxycytidine treatment, indicating that TIG1 expression is transcriptionally silenced in these cancer cells by abnormal DNA hypermethylation. These data indicate that TIG1 undergoes frequent epigenetic inactivation due to aberrant DNA hypermethylation in gastric cancers, and its altered expression is associated with the malignant progression of tumors.

Involvement of tazarotene‐induced gene 1 in proliferation and differentiation of human adipose tissue‐derived mesenchymal stem cells

Mesenchymal stem cells (MSC) have both self-renewal and multilineage differentiation potential, and bone marrow-derived MSC have been applied for tissue regeneration and repair. Although adipose tissue-derived MSC (ASC) have emerged as an alternative cell source, little information is available regarding the biologic difference between ASC derived from visceral and subcutaneous fat. Therefore, we aimed to compare the proliferation and gene expression profile of cultured human visceral ASC (VASC) and subcutaneous ASC (SASC), and to identify a novel gene involved in proliferation and differentiation of ASC. We performed microarray analysis of cultured VASC and SASC, and investigated the role of tazarotene-induced gene 1 (TIG1), a most differentially expressed gene, in the proliferation and differentiation of ASC. SASC proliferated faster than VASC for over 10 passages, and TIG1 expression was consistently up-regulated in VASC of humans, rats and mice. Overexpression of the TIG1 gene in human SASC inhibited cell proliferation, whereas knockdown of TIG1 expression by siRNA promoted cell proliferation. In addition, overexpression of the TIG1 gene in SASC enhanced their differentiation into adipocytes, and promoted up-regulation of peroxisome proliferators-activated receptor gamma and CCAAT/enhancer binding protein alpha. On the other hand, TIG1 overexpression in SASC inhibited their differentiation into osteocytes and the expression of osteocalcin. TIG1 plays an important role in regulating proliferation and differentiation of ASC.

13-cis Retinoic Acid Induces Apoptosis and Cell Cycle Arrest in Human SEB-1 Sebocytes

Isotretinoin (13-cis retinoic acid (13-cis RA)) is the most potent inhibitor of sebum production, a key component in the pathophysiology of acne, yet its mechanism of action remains largely unknown. The effects of 13-cis RA, 9-cis retinoic acid (9-cis RA), and all-trans retinoic acid (ATRA) on cell proliferation, apoptosis, and cell cycle proteins were examined in SEB-1 sebocytes and keratinocytes. 13-cis RA causes significant dose-dependent and time-dependent decreases in viable SEB-1 sebocytes. A portion of this decrease can be attributed to cell cycle arrest as evidenced by decreased DNA synthesis, increased p21 protein expression, and decreased cyclin D1. Although not previously demonstrated in sebocytes, we report that 13-cis RA induces apoptosis in SEB-1 sebocytes as shown by increased Annexin V-FITC staining, increased TUNEL staining, and increased cleaved caspase 3 protein. Furthermore, the ability of 13-cis RA to induce apoptosis cannot be recapitulated by 9-cis RA or ATRA, and it is not inhibited by the presence of a retinoid acid receptor (RAR) pan-antagonist AGN 193109. Taken together these data indicate that 13-cis RA causes cell cycle arrest and induces apoptosis in SEB-1 sebocytes by a RAR-independent mechanism, which contributes to its sebosuppressive effect and the resolution of acne.

DNA methylation of genes linked to retinoid signaling in squamous cell carcinoma of the esophagus: DNA methylation of CRBP1 and TIG1 is associated with tumor stage

Hypermethylation of CpG islands is associated with the silencing of various tumor suppressor genes. Retinoic acid receptor-beta (RAR-beta), cellular retinol-binding protein 1 (CRBP1), and tazarotene-induced gene 1 (TIG1) have been linked to retinoic acid signaling. Little is known about the involvement of these three genes in esophageal squamous cell carcinoma (ESCC). In this study, we investigated the methylation status of these genes and analyzed the role of methylation of their DNA in ESCC. Methylation-specific polymerase chain reaction (PCR) was performed to study the methylation of CpG islands in 28 ESCC (stages I, II, and III) and 10 samples of corresponding non-neoplastic mucosa. The mRNA expression levels of the three genes were measured by quantitative reverse transcription-PCR. DNA hypermethylation of RAR-beta was found in seven (25.0%) of the 28 ESCC, of CRBP1 in five (17.9%), and of TIG1 in five (17.9%). DNA methylation of RAR-beta was identified in one of 10 samples of corresponding non-neoplastic mucosa (10.0%), whereas no DNA methylation of CRBP1 or TIG1 was detected. In total, at least one of the three genes was hypermethylated in 12 (42.9%) ESCC. Reduced expression of RAR-beta, CRBP1, and TIG1 was found in 14 (50.0%), 15 (53.6%), and 13 (46.4%) ESCC, respectively. DNA methylation of each gene was significantly associated with reduced expression of the respective mRNA. No correlation was found between the DNA methylation status of RAR-beta and clinicopathological factors such as depth of invasion, lymph node metastasis, or tumor stage. In contrast, DNA methylation of both CRBP1 and TIG1 was observed only in stage III ESCC. These results show that inactivation of the retinoic acid signaling-associated genes RAR-beta, CRBP1, and TIG1 by DNA methylation occurs frequently in ESCC.

Silencing of the retinoid response gene TIG1 by promoter hypermethylation in nasopharyngeal carcinoma.

Tazarotene-induced gene 1 (TIG1) and Tazarotene-induced gene 3 (TIG3) are retinoid acid (RA) target genes as well as candidate tumor suppressor genes in human cancers. In our study, we have investigated the expression of TIG1 and TIG3 in nasopharyngeal carcinoma (NPC). Loss of TIG1 expression was found in 80% of NPC cell lines and 33% of xenografts, whereas TIG3 was expressed in all NPC samples and immortalized nasopharyngeal epithelial cells. In order to elucidate the epigenetic silencing of TIG1 in NPC, the methylation status of TIG1 promoter was examined by genomic bisulfite sequencing and methylation-specific PCR (MSP). We have detected dense methylation of TIG1 5'CpG island in the 5 TIG1-negative NPC cell lines and xenograft (C666-1, CNE1, CNE2, HONE1 and X666). Partial methylation was observed in 1 NPC cell line HK1 showing dramatic decreased in TIG1 expression. Promoter methylation was absent in 2 TIG1-expressed NPC xenografts and the normal epithelial cells. Restoration of TIG1 expression and unmethylated alleles were observed in NPC cell lines after 5-aza-2'-deoxycytidine treatment. Moreover, the methylated TIG1 sequence was detected in 39 of 43 (90.7%) primary NPC tumors by MSP. In conclusion, our results showed that TIG1 expression is lost in the majority of NPC cell lines and xenografts, while promoter hypermethylation is the major mechanism for TIG1 silencing. Furthermore, the frequent epigenetic inactivation of TIG1 in primary NPC tumors implied that it may play an important role in NPC tumorigenesis.

Hypermethylation and silencing of the putative tumor suppressor Tazarotene-induced gene 1 in human cancers.

A variety of tumor suppressor genes are down-regulated by hypermethylation during carcinogenesis. Using methylated CpG amplification-representation difference analysis, we identified a DNA fragment corresponding to the Tazarotene-induced gene 1 (TIG1) promoter-associated CpG island as one of the genes hypermethylated in the leukemia cell line K562. Because TIG1 has been proposed to act as a tumor suppressor, we tested the hypothesis that cytosine methylation of the TIG1 promoter suppresses its expression and causes a loss of responsiveness to retinoic acid in some neoplastic cells. We examined TIG1 methylation and expression status in 53 human cancer cell lines and 74 primary tumors, including leukemia and head and neck, breast, colon, skin, brain, lung, and prostate cancer. Loss of TIG1 expression was strongly associated with TIG1 promoter hypermethylation (P < 0.001). There was no correlation between TIG1 promoter methylation and that of retinoid acid receptor beta2 (RARbeta2), another retinoic-induced putative tumor suppressor gene (P = 0.78). Treatment with the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine for 5 days restored TIG1 expression in all eight silenced cell lines tested. TIG1 expression was also inducible by treatment with 1 micro M all-trans-retinoic acid for 3 days except in densely methylated cell lines. Treatment of the K562 leukemia cells with demethylating agent combined with all-trans-retinoic acid induced apoptosis. These findings indicate that silencing of TIG1 promoter by hypermethylation is common in human cancers and may contribute to the loss of retinoic acid responsiveness in some neoplastic cells.

Tazarotene-induced gene 1 (TIG1) expression in prostate carcinomas and its relationship to tumorigenicity.

Prostate cancer is the most common noncutaneous male cancer and one of the least understood malignant diseases. Identifying key genetic factors involved in the metastasis of prostate cancer cells is critical. In this study, we used selective subtractive differential gene display to identify a gene whose decreased expression may contribute to the growth and expansion of prostate cancer. We used 192 primer pair combinations and polymerase chain reaction technology to identify genes expressed in the benign prostate cell line PNT-2 but not in the malignant prostate cancer cell lines LNCaP, Du-145, PC-3, or PC-3M. The tazarotene-induced gene 1 (TIG1) was chosen for further study. TIG1 expression in normal tissues and cell lines was analyzed by northern blot and in normal and tumor prostate tissue sections by in situ hybridization. The in vitro invasiveness (migration through extracellular matrix) and in vivo tumorigenicity (growth in nude mice) were assessed for the highly malignant PC-3M cell line transfected with TIG1 or control cDNA. All statistical tests were two-sided. TIG1 mRNA was expressed in a variety of normal tissues other than prostate tissue. TIG1 mRNA was detected in all 10 normal human prostate tissues and all 51 benign prostatic hyperplastic tissues analyzed but in only four of 51 malignant prostate tissues analyzed. Compared with vector-transfected cells, transfection of PC-3M cells with TIG1 decreased in vitro invasiveness from 14.7% to 3.7%, (mean difference = 11%; 95% confidence interval [CI] = 9.2% to 12.8%, P<.001) and decreased in vivo tumorigenicity from an average tumor weight of 1.31 g to 0.55 g, (mean difference = 0.76 g; 95% CI = 0.43 to 1.09 g, P<.001). TIG1 may be a tumor suppressor gene whose diminished expression is involved in the malignant progression of prostate cancer.

Tazarotene-Induced Gene 1 (TIG1), a Novel Retinoic Acid Receptor-Responsive Gene in Skin

Retinoids exert their effect through ligand-dependent transcription factors, retinoic acid receptors (RARalpha, beta, and gamma) and retinoid X receptor (RXRalpha, beta, and gamma), which belong to the superfamily of steroid/thyroid/vitamin D3, nuclear receptors. Using a subtraction hybridization approach, we have identified a cDNA sequence, Tazarotene Induced Gene 1 (TIG1), which is highly upregulated in skin raft cultures by an RARbeta/gamma -selective retinoid AGN 190168 (tazarotene/ethyl 6-[2-(4,4-dimethylthiochroman-6-yl)-ethynyl]nicotinate), which is effective in the treatment of psoriasis. The retinoid-mediated upregulation in the expression of TIG1 was confirmed by Southern and Northern analyses. Upon sequencing, TIG1 was found to be a novel cDNA which encodes a protein of 228 amino acids whose sequence suggests that is a transmembrane protein with a small N-terminal intracellular region, a single membrane-spanning hydrophobic region, and a large C-terminal extracellular region containing a glycosylation signal. We demonstrate that TIG1 is also upregulated by AGN 190168 in skin raft cultures prepared from psoriatic fibroblasts and normal keratinocytes and in primary fibroblast and keratinocyte cultures. We also show that TIG1 is upregulated by retinoic acid receptor but not by retinoid X receptor-specific synthetic retinoids. Finally, we demonstrate that TIG1 is induced by AGN 190168 in psoriatic lesions during the course of clinical treatment of the disease.