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

Phospholipase A and acyltransferase 4/retinoic acid receptor responder 3 at the intersection of tumor suppression and pathogen restriction

Phospholipase A and acyltransferase (PLAAT) 4 is a class II tumor suppressor with phospholipid metabolizing abilities. It was characterized in late 2000s, and has since been referred to as ‘tazarotene-induced gene 3’ (TIG3) or ‘retinoic acid receptor responder 3’ (RARRES3) as a key downstream effector of retinoic acid signaling. Two decades of research have revealed the complexity of its function and regulatory roles in suppressing tumorigenesis. However, more recent findings have also identified PLAAT4 as a key anti-microbial effector enzyme acting downstream of interferon regulatory factor 1 (IRF1) and interferons (IFNs), favoring protection from virus and parasite infections. Unveiling the molecular mechanisms underlying its action may thus open new therapeutic avenues for the treatment of both cancer and infectious diseases. Herein, we aim to summarize a brief history of PLAAT4 discovery, its transcriptional regulation, and the potential mechanisms in tumor prevention and anti-pathogen defense, and discuss potential future directions of PLAAT4 research toward the development of therapeutic approaches targeting this enzyme with pleiotropic functions.

Interferon-α2b-Induced RARRES3 Upregulation Inhibits Hypertrophic Scar Fibroblasts' Proliferation and Migration Through Wnt/β-Catenin Pathway Suppression

Hypertrophic scar (HS) is a severe skin fibrotic disorder with unclear pathogenesis. Interferon-α2b (IFN-α2b) exerts inhibitory effects on HS in vivo and in vitro; however, the exact mechanism remains unclear. In this study, we aimed to evaluate the inhibitory effects of IFN-α2b on hypertrophic scar fibroblasts' (HSFs) proliferation and migration, and to further investigate the associated molecular mechanism. Cell Counting Kit-8 and CyQUANT assays were used to assess HSFs' proliferation; wound healing and Transwell assays were used to assess HSFs' migration; real-time quantitative polymerase chain reaction and Western blotting were used to detect messenger RNA and protein levels, respectively, of related genes; bioinformatics analysis was performed to predict the downstream target of IFN-α2b. Our findings are as follows: (1) IFN-α2b inhibited HSFs' proliferation and migration in a dose-dependent manner. (2) IFN-α2b inhibited HSFs' proliferation and migration by suppressing the Wnt/β-catenin pathway. (3) Retinoic-acid receptor responder 3 (RARRES3) was predicted as a functional downstream molecule of IFN-α2b, which was low in HSFs. (4) IFN-α2b inhibited HSF phenotypes and the Wnt/β-catenin pathway by upregulating RARRES3 expression. (5) RARRES3 restrained HSFs' proliferation and migration by repressing the Wnt/β-catenin pathway. In conclusion, IFN-α2b-induced RARRES3 upregulation inhibited HSFs' proliferation and migration through Wnt/β-catenin pathway suppression.

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.

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.

Polyethylene glycol improves current methods for circulating extracellular vesicle-derived DNA isolation

BACKGROUND

Extracellular vesicles (EVs) are small membrane-bound vesicles which play an important role in cell-to-cell communication. Their molecular cargo analysis is presented as a new source for biomarker detection, and it might provide an alternative to traditional solid biopsies. However, the most effective approach for EV isolation is not yet well established.

RESULTS

Here, we study the efficiency of the most common EV isolation methods-ultracentrifugation, Polyethlyene glycol and two commercial kits, Exoquick® and PureExo®. We isolated circulating EVs from the bloodstream of healthy donors, characterized the size and yield of EVs and analyzed their protein profiles and concentration. Moreover, we have used for the first time Digital-PCR to identify and detect specific gDNA sequences, which has several implications for diagnostic and monitoring many types of diseases.

CONCLUSIONS

Our findings present Polyethylene glycol precipitation as the most feasible and less cost-consuming EV isolation technique.

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.

Histone methyltransferase G9a promotes liver cancer development by epigenetic silencing of tumor suppressor gene RARRES3

BACKGROUND & AIMS

Hepatocellular carcinoma (HCC) is a major leading cause of cancer mortality worldwide. Epigenetic deregulation is a common trait of human HCC. G9s is an important epigenetics regulator however, its role in liver carcinogenesis remains to be investigated.

METHODS

Gene expressions were determined by RNA-Seq and qRT-PCR. G9a knockdown and knockout cell lines were established by lentiviral-based shRNA and CRISPR/Cas9 gene editing system. Tumor-promoting functions of G9a was studied in both HCC cell lines and nude mice model. The downstream targets of G9a were identified by RNA-Seq and confirmed by ChIP assay. The therapeutic value of G9a inhibitors was evaluated both in vitro and in vivo.

RESULTS

We identified G9a as a frequently upregulated histone methyltransferase in human HCCs. Upregulation of G9a was significantly associated with HCC progression and aggressive clinicopathological features. Functionally, we demonstrated that inactivation of G9a by RNAi knockdown, CRISPR/Cas9 knockout, and pharmacological inhibition remarkably abolished H3K9 di-methylation and suppressed HCC cell proliferation and metastasis in both in vitro and in vivo models. Mechanistically, we showed that the frequent upregulation of G9a in human HCCs was attributed to gene copy number gain at chromosome 6p21. In addition, we identified miR-1 as a negative regulator of G9a. Loss of miR-1 relieved the post-transcriptional repression on G9a and contributed to its upregulation in human HCC. Utilizing RNA sequencing, we identified the tumor suppressor RARRES3 as a critical target of G9a. Epigenetic silencing of RARRES3 contributed to the tumor-promoting function of G9a.

CONCLUSION

This study shows a frequent deregulation of miR-1/G9a/RARRES3 axis in liver carcinogenesis, highlighting the pathological significance of G9a and its therapeutic potential in HCC treatment. Lay summary: In this study, we identified G9a histone methyltransferase was frequently upregulated in human HCC and contributes to epigenetic silencing of tumor suppressor gene RARRES3 in liver cancer. Targeting G9a may be a novel approach for HCC treatment.

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.

H-rev107 Regulates Cytochrome P450 Reductase Activity and Increases Lipid Accumulation

H-rev107 is a member of the HREV107 type II tumor suppressor gene family and acts as a phospholipase to catalyze the release of fatty acids from glycerophospholipid. H-rev107 has been shown to play an important role in fat metabolism in adipocytes through the PGE2/cAMP pathway, but the detailed molecular mechanism underlying H-rev107-mediated lipid degradation has not been studied. In this study, the interaction between H-rev107 and cytochrome P450 reductase (POR), which is involved in hepatic lipid content regulation, was determined by yeast two-hybrid screen and confirmed by using in vitro pull down assays and immunofluorescent staining. The expression of POR in H-rev107-expressing cells enhanced the H-rev107-mediated release of arachidonic acid. However, H-rev107 inhibited POR activity and relieved POR-mediated decreased triglyceride content in HtTA and HeLa cervical cells. The inhibitory effect of H-rev107 will be abolished when POR-expressing cells transfected with PLA₂-lacking pH-rev107 or treated with PLA₂ inhibitor. Silencing of H-rev107 using siRNA resulted in increased glycerol production and reversion of free fatty acid-mediated growth suppression in Huh7 hepatic cells. In summary, our results revealed that H-rev107 is also involved in lipid accumulation in liver cells through the POR pathway via its PLA₂ activity.

RARRES3 suppressed metastasis through suppression of MTDH to regulate epithelial-mesenchymal transition in colorectal cancer

It has been reported that Retinoic acid receptor responder 3 (RARRES3) could suppress the metastasis of colorectal cancer (CRC). However, the underlying mechanism by which RARRES3 suppresses metastasis remains unknown. To investigate the functional involvement of RARRES3 in CRC, we first analyzed the expression of this protein between human CRC clinical samples and their corresponding normal controls and tested its correlation with clinicopathology as well as prognosis of CRC. We also examined the endogenous expression of RARRES3 by western-blot in a panel of CRC cell lines with different metastatic capacity. Cell proliferation, migration and invation of the CRC cell lines with either knockdown or reexpression of RARRES3 were examined by MTT, transwell and wound healing assays, respectively. The intrecellular signaling pathways affected by manipulations of RARRES3 in CRC cells were determined by western blot. Immunoprecipitation (IP) was employed to assess the interactionbetween proteins. To investigate the metastatic ability in vivo, CRC cell lines with manipulations of RARRES3 expression were inoculated in nude mice through tail vein injection. We confirmed that RARRES3 was significantly down-regulated in CRC tissues compared with normal controls. RARRES3 expression was not correlated with prognosis but significantly associated with CRC differentiation and lymphnodes metastases. We also found that RARRES3 was able to significantly suppress the metastasis of CRC cells both in vitro and in vivo through the regulation of epithelial-mesenchymal transition (EMT) process during which RARRES3 interactedwith MTDH in an opposite way. Taken together, we for the first time found that RARRES3 was able to suppress the metastasis of CRC both in vitro and in vivo via suppression of MTDH so as to regulate EMT.

Structural and functional characterization of tumor suppressors TIG3 and H-REV107

H-REV107-like family proteins TIG3 and H-REV107 are class II tumor suppressors. Here we report that the C-terminal domains (CTDs) of TIG3 and H-REV107 can induce HeLa cell death independently. The N-terminal domain (NTD) of TIG3 enhances the cell death inducing ability of CTD, while NTD of H-REV107 plays an inhibitory role. The solution structure of TIG3 NTD is very similar to that of H-REV107 in overall fold. However, the CTD binding regions on NTD are different between TIG3 and H-REV107, which may explain their functional difference. As a result, the flexible main loop of H-REV107, but not that of TIG3, is critical for its NTD to modulate its CTD in inducing cell death.

Phospholipase A/Acyltransferase enzyme activity of H-rev107 inhibits the H-RAS signaling pathway

BACKGROUND

H-rev107, also called HRASLS3 or PLA2G16, is a member of the HREV107 type II tumor suppressor gene family. Previous studies showed that H-rev107 exhibits phospholipase A/acyltransferase (PLA/AT) activity and downregulates H-RAS expression. However, the mode of action and the site of inhibition of H-RAS by H-rev107 are still unknown.

RESULTS

Our results indicate that H-rev107 was co-precipitated with H-RAS and downregulated the levels of activated RAS (RAS-GTP) and ELK1-mediated transactivation in epidermal growth factor-stimulated and H-RAS-cotransfected HtTA cervical cancer cells. Furthermore, an acyl-biotin exchange assay demonstrated that H-rev107 reduced H-RAS palmitoylation. H-rev107 has been shown to be a PLA/AT that is involved in phospholipid metabolism. Treating cells with the PLA/AT inhibitor arachidonyl trifluoromethyl ketone (AACOCF3) or methyl arachidonyl fluorophosphate (MAFP) alleviated H-rev107-induced downregulation of the levels of acylated H-RAS. AACOCF3 and MAFP also increased activated RAS and ELK1-mediated transactivation in H-rev107-expressing HtTA cells following their treatment with epidermal growth factor. In contrast, treating cells with the acyl-protein thioesterase inhibitor palmostatin B enhanced H-rev107-mediated downregulation of acylated H-RAS in H-rev107-expressing cells. Palmostatin B had no effect on H-rev107-induced suppression of RAS-GTP levels or ELK1-mediated transactivation. These results suggest that H-rev107 decreases H-RAS activity through its PLA/AT activity to modulate H-RAS acylation.

CONCLUSIONS

We made the novel observation that H-rev107 decrease in the steady state levels of H-RAS palmitoylation through the phospholipase A/acyltransferase activity. H-rev107 is likely to suppress activation of the RAS signaling pathway by reducing the levels of palmitoylated H-RAS, which decreases the levels of GTP-bound H-RAS and also the activation of downstream molecules. Our study further suggests that the PLA/AT activity of H-rev107 may play an important role in H-rev107-mediated RAS suppression.

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.

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.

H-rev107 regulates prostaglandin D2 synthase-mediated suppression of cellular invasion in testicular cancer cells

Background

H-rev107 is a member of the HREV107 type II tumor suppressor gene family which includes H-REV107, RIG1, and HRASLS. H-REV107 has been shown to express at high levels in differentiated tissues of post-meiotic testicular germ cells. Prostaglandin D2 (PGD2) is conjectured to induce SRY-related high-mobility group box 9 (SOX9) expression and subsequent Sertoli cell differentiation. To date, the function of H-rev107 in differentiated testicular cells has not been well defined.

Results

In the study, we found that H-rev107 was co-localized with prostaglandin D2 synthase (PTGDS) and enhanced the activity of PTGDS, resulting in increase of PGD2 production in testis cells. Furthermore, when H-rev107 was expressed in human NT2/D1 testicular cancer cells, cell migration and invasion were inhibited. Also, silencing of PTGDS would reduce H-rev107-mediated increase in PGD2, cAMP, and SOX9. Silencing of PTGDS or SOX9 also alleviated H-rev107-mediated suppression of cell migration and invasion.

Conclusions

These results revealed that H-rev107, through PTGDS, suppressed cell migration and invasion. Our data suggest that the PGD2-cAMP-SOX9 signal pathway might play an important role in H-rev107-mediated cancer cell invasion in testes.

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.