Downregulation of HER2 by RIG1 involves the PI3K/Akt pathway in ovarian cancer cells

The PLAAT family as phospholipid-related enzymes

The phospholipase A and acyltransferase (PLAAT) family is a group of structurally related proteins that are conserved among vertebrates. In humans, the family comprises five members (PLAAT1-5), which share common domain structures, and functions as phospholipase A1/A2 and acyltransferase enzymes. Regarding acyltransferase activities, PLAATs produce N-acyl-phosphatidylethanolamines, which serve as the precursor of bioactive N-acylethanolamines (NAEs). Recent evidence strongly suggests that PLAAT proteins play a crucial role in maintaining homeostasis in various organelles, such as the endoplasmic reticulum, lysosomes, mitochondria, and peroxisomes. In this process, PLAAT proteins bind to organelles and degrade them in an enzyme activity-dependent manner. Their physiological significance was revealed by the inability of PLAAT-deficient animals to degrade organelles during the maturation of the eye lens, resulting in the development of cataracts. Furthermore, the deficiency of PLAAT1, 3, and 5 in mice caused resistance to high-fat diet-induced fatty liver, the lean phenotype represented by a marked decrease in adipose tissue mass, and the exacerbation of testicular inflammation due to decreased levels of anti-inflammatory NAEs, respectively. In addition, human PLAAT3 was identified as a causative gene for lipodystrophy. We herein provide an overview of the molecular and biological properties of PLAAT proteins.

Molecular Mechanisms Associated with the Development of the Metritis Complex in Dairy Cattle

The metritis complex (MC), a group of post-partum uterine diseases, is associated with increased treatment costs and reduced milk yield and fertility. The goal of this study was to identify genetic variants, genes, or genomic regions that modulate MC disease. A genome-wide association study was performed using a single-locus mixed linear model of 1967 genotypes (624,460 SNPs) and metritis complex records. Then, in-silico functional analyses were performed to detect biological mechanisms and pathways associated with the development of MC. The ATP8A2, COX16, AMN, and TRAF3 genes, located on chromosomes 12, 10, and 21, were associated with MC at p ≤ 0.0001. These genes are involved in the regulation of cholesterol metabolism in the stromal tissue of the uterus, which can be directly associated with the mode of transmission for pathogens causing the metritis complex. The modulation of cholesterol abundance alters the efficiency of virulence factors and may affect the susceptibility of the host to infection. The SIPA1L1, DEPDC5, and RNF122 genes were also significantly associated with MC at p ≤ 0.0001 and are involved in the PI3k-Akt pathway, responsible for activating the autophagic processes. Thus, the dysregulation of these genes allows for unhindered bacterial invasion, replication, and survival within the endometrium.

Regulation of cGAS-STING signalling in cancer: Approach for combination therapy

Innate immunity plays an important role not only during infection but also homeostatic role during stress conditions. Activation of the immune system including innate immune response plays a critical role in the initiation and progression of tumorigenesis. The innate immune sensor recognizes pathogen-associated molecular patterns (PAMPs) and activates cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) (cGAS-STING) and induces type-1 immune response during viral and bacterial infection. cGAS-STING is regulated differently in conditions like cellular senescence and DNA damage in normal and tumor cells and is implicated in the progression of tumors from different origins. cGAS binds to cytoplasmic dsDNA and synthesize cyclic GMP-AMP (2'3'-cGAMP), which selectively activates STING and downstream IFN and NF-κB activation. We here reviewed the cGAS-STING signalling pathway and its cross-talk with other pathways to modulate tumorigenesis. Further, the review also focused on emerging studies that targeted the cGAS-STING pathway for developing targeted therapeutics and combinatorial regimens for cancer of different origins.

Baicalein suppresses HER2-mediated malignant transformation of HER2-overexpressing ovarian cancer cells by downregulating HER2 gene expression

The upregulation of the HER2 oncogene is associated with a variety of human cancers and is associated with poor prognosis. Baicalein is reported to have anti-tumor activity, but the molecular mechanism of this effect in HER2-positive cancer cells has not been studied. In this study, our data showed that baicalein can inhibit the proliferation and transformation potential of ovarian cancer cells overexpressing HER2. Baicalein treatment caused a dose-dependent inhibition of HER2 gene expression at the transcriptional level. Baicalein acted on ovarian cancer cells overexpressing HER2 to downregulate the PI3K/Akt signaling pathway downstream of HER2 and inhibit the expression or activity of downstream targets, such as VEGF and cyclin D1 and MMP2. Oral administration of baicalein supplemented with a pharmaceutical excipient significantly inhibited the growth of HER2-overexpressing ovarian SKOV-3 cancer xenografts in mice. These results suggest that downregulation of HER2 gene expression by baicalein at the transcriptional level contributes to inhibit the in vitro and in vivo proliferation and HER2-mediated malignant transformation of HER2-overexpressing ovarian cancer cells.

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.

Long noncoding RNA HCP5 suppresses skin cutaneous melanoma development by regulating RARRES3 gene expression via sponging miR-12

Objective

This research aimed to investigate the role and mechanism of long noncoding RNA (lncRNA) HCP5 in skin cutaneous melanoma (SKCM).

Materials and methods

Survival analysis was performed using The Cancer Genome Atlas (TCGA)-SKCM data and SKCM patients’ clinical data. Primary SKCM cells were derived from patients’ pathologic tissue specimens. HCP5 overexpression was achieved by lentiviral transduction. Malignancy of SKCM cells was evaluated in vitro by cell proliferation, colony formation, apoptosis and transwell invasion assays. RARRES3 knockdown was achieved by siRNA transfection. DIANA microT-CDS algorithm was used to predict miRNAs that might interact with HCP5 and 3ʹ untranslated region of RARRES3 mRNA. microRNA target luciferase reporter assay and AGO2-RNA immunoprecipitation were used to verify the interaction between HCP5, 3ʹ UTR of RARRES3 mRNA and miR-1286.

Results

HCP5 level was decreased in SKCM tissue specimens compared to noncancerous counterparts. Low expression of HCP5 was associated with SKCM patients’ poor overall survival and disease progression. HCP5 overexpression significantly reduced the malignancy of primary SKCM cells in vitro. RARRES3 was found as a HCP5-co-expressing gene in SKCM cells. HCP5 overexpression significantly increased RARRES3 expression in SKCM cells. RARRES3 knockdown partially abolished the anti-SKCM effect of HCP5 overexpression. MiR-1286 was found interacting with both HCP5 and 3ʹ UTR of RARRES3 mRNA.

Conclusion

HCP5 is a cancer-suppressive lncRNA in SKCM. HCP5 overexpression decreased SKCM cell malignancy in vitro by upregulating RARRES3, possibly via sponging miR-1286.

Basal expression of interferon regulatory factor 1 drives intrinsic hepatocyte resistance to multiple RNA viruses

Current paradigms of cell intrinsic immunity to RNA viruses center on virus-triggered inducible antiviral responses initiated by RIG-I-like receptors (RLRs) or Toll-like receptors (TLRs) that sense pathogen-associated molecular patterns, and signal downstream through interferon regulatory factors (IRFs), transcription factors that induce synthesis of type I and type III interferons (IFNs)1. RNA viruses have evolved sophisticated strategies to disrupt these signaling pathways and evade elimination by cells, attesting to their importance2. Less attention has been paid how IRFs maintain basal levels of protection against viruses. Here, we depleted antiviral factors linked to RLR and TLR signaling in order to map critical host pathways restricting positive-strand RNA virus replication in immortalized hepatocytes and identified an unexpected role for IRF1. We show constitutively expressed IRF1 acts independently of MAVS, IRF3, and STAT1-dependent signaling to provide intrinsic antiviral protection in actinomycin D-treated cells. IRF1 localizes to the nucleus, where it maintains basal transcription of a suite of antiviral genes that protect against multiple pathogenic RNA viruses, including hepatitis A and C viruses (HAV and HCV), dengue virus (DENV) and Zika virus (ZIKV). Our findings reveal an unappreciated layer of hepatocyte intrinsic immunity to these positive-strand RNA viruses, and identify previously unrecognized antiviral effector genes.

Concerted action of histone methyltransferases G9a and PRMT-1 regulates PGC-1α-RIG-I axis in IFNγ treated glioma cells

IFNγ induced de-differentiation markers are negatively regulated by retinoic acid inducible gene (RIG-I) in glioma cells. In addition to RIG-I, IFNγ treatment increased H3K9me2; histone methyltransferases (HMTs) G9a and protein arginine methyltransferase-1 (PRMT-1) levels. While G9a inhibition further increased IFNγ induced RIG-I, PRMT-1 inhibition abrogated IFNγ elevated RIG-I levels. IFNγ induced Sp1 and NFκB served as negative regulators of RIG-I, with decreased occupancy of Sp1 and NFκB observed on the RIG-I promoter. A diminished H3K9Me2 enrichment was observed at the NFκB but not at Sp-1 binding site. IFNγ induced PPAR gamma coactivator-1 alpha (PGC-1α) positively regulated RIG-I; with PRMT-1 and G9a affecting PGC-1α in a counter-regulatory manner. These findings demonstrate how concerted action of HMTs aid PGC-1α driven RIG-I for the sustenance of glioma cells in a de-differentiated state.

CK2 induced RIG-I drives metabolic adaptations in IFNγ-treated glioma cells

Given the known anti-tumorigenic properties of IFNγ, its effect on glioma cell survival was investigated. Though IFNγ had no effect on glioma cell viability, it induced cell cycle arrest. This was accompanied by increased expression of p53 and retinoic acid inducible gene (RIG-I). While RIG-I had no effect on glioma cell survival, it increased expression of p53 and its downstream target TP53 induced glycolysis and apoptosis regulator (TIGAR). IFNγ induced mitochondrial co-localization of RIG-I was concomitant with its ability to regulate ROS generation, oxidative phosphorylation (OXPHOS) and key enzymes involved in glycolysis and pentose phosphate pathway. Importantly, metabolic gene profiling indicated a suppressed glycolytic pathway in glioma cells upon IFNγ treatment. In addition, IFNγ mediated increase in casein kinase 2 (CK2) expression positively regulated RIG-I expression. These findings demonstrate how IFNγ induced CK2 regulates RIG-I to drive a complex program of metabolic adaptation and redox homeostasis, crucial for determining glioma cell fate.

Exendin-4 inhibits growth and augments apoptosis of ovarian cancer cells

Glucagon-like peptide (GLP)-1 promotes proliferation and survival in β-cell; however, whether GLP-1 receptor agonists promote growth of human ovarian cancer cells remain unknown. We aimed to explore the effects of GLP-1 agents on ovarian cancer cells. GLP-1 receptor expression in human ovarian cancer tissues was detected by immunohistochemical analysis. The effects of exendin-4, a GLP-1R agonist, were investigated on proliferation, migration and invasion, apoptosis in vitro and tumor formation in nude mice of ovarian cancer cells. Our study demonstrated that GLP-1R expressed in both human ovarian cancer tissues and cell lines. Exendin-4 inhibited growth, migration and invasion and enhanced apoptosis of ovarian cancer cells through inhibition of the PI3K/Akt pathway. And exendin-4 attenuated tumor formation by ovarian cancer cells in vivo. Our study suggests that GLP-1R agonists do not promote the growth of ovarian cancer and may even have anticancer effect on selected diabetic patients with ovarian cancer.

Tumor-Suppressor Gene NBPF1 Inhibits Invasion and PI3K/mTOR Signaling in Cervical Cancer Cells

The purpose of this study was to assess the effects of NBPF1 expression on cervical cancer cell invasion and apoptosis and to illustrate its potential mechanism. Human cervical cancer HeLa cells were transfected with the constructed siNBPF1 or pcDNA3.1-NBPF1 vectors. Effects of NBPF1 expression on cell invasion ability and cell apoptosis were analyzed using the Matrigel method and an Annexin V-FITC cell apoptosis kit, respectively. In addition, cell apoptosis-related proteins involved with the PI3K/mTOR signaling pathway were analyzed using Western blot. Remediation experiments were conducted to verify the effects of NBPF1 expression on cell invasion and apoptosis. Compared to the control, mRNA and protein expressions of NBPF1 were significantly decreased when cells were transfected with siNBPF1 (p < 0.05), which was contrary to the results of cells transfected with pcDNA3.1-NBPF1. Overexpression of NBPF1 significantly suppressed HeLa cell invasion but promoted cell apoptosis (p < 0.05). Overexpression of NBPF1 performed a significant inhibitory role on PI3K/mTOR signal pathway expression, while NBPF1 was silenced, showing contrary results. Our data suggested that NBPF1 overexpression may be a suppressor for cervical cancer via affecting cell invasion and apoptosis through regulating PI3K/mTOR signaling pathway. NBPF1 may be a potential therapeutic target for cervical cancer treatment.

TDRG1 functions in testicular seminoma are dependent on the PI3K/Akt/mTOR signaling pathway

Human testis development-related gene 1 (TDRG1) is a recently identified gene that is expressed exclusively in the testes and promotes the development of testicular germ cell tumors. In this study, the role of TDRG1 in the development of testicular seminoma, which is the most common testicular germ cell tumor, was further investigated. Based on polymerase chain reaction, Western blotting, and immunohistochemistry tests, both gene and protein expression levels of TDRG1 were significantly upregulated in testicular seminoma tissues compared with normal testicular tissues. Additionally, the levels of phosphoinositide-3 kinase (PI3K)/p110 and Akt phosphorylation were dramatically upregulated in testicular seminoma tissues. Accordingly, in our cell experiment, seminoma TCam-2 cells were subjected to different treatments: the TDRG1 knockout, TDRG1 overexpression, PI3K inhibition (LY294002 administration), or PI3K activation (insulin-like growth factor-1 administration). Cell proliferation, the proliferation index, apoptosis rate, cell adhesive capacity, and cell invasion capability were assessed. Cells with both TDRG1 knockout and PI3K inhibition exhibited decreased cell proliferation, proliferation indexes, cell adhesion capacity, and cell invasion capability and increased apoptosis rates. Most of these effects were reversed by TDRG1 overexpression or PI3K activation, indicating that both TDRG1- and PI3K-mediated signaling promote proliferation and invasion of testicular seminoma cells. The knockout of TDRG1 significantly decreased the phosphorylation levels of PI3K/p85, PI3K/p110, Akt, and mammalian target of rapamycin (mTOR; Ser²⁴⁴⁸). Except for PI3K/p110, TDRG1 overexpression had the opposite effects on phosphorylation levels. Phosphorylated mTOR at Ser²⁴⁸¹ and Thr²⁴⁴⁶ was not affected by TDRG1 or PI3K in our tests. Thus, these results indicate that TDRG1 promotes the development and migration of seminoma cells via the regulation of the PI3K/Akt/mTOR signaling pathway; this contributes to an understanding of the precise mechanisms underlying the development and migration of seminomas and lays a theoretical foundation for the development of appropriate therapies.

Involvement of RARRES3 in the regulation of Wnt proteins acylation and signaling activities in human breast cancer cells

The Wnt/β-catenin signaling pathway has emerged as a key regulator of complex biological processes, such as embryonic development, cell proliferation, cell fate decision and tumorigenesis. Recent studies have shown that the deregulation of Wnt/β-catenin signaling is frequently observed and leads to abnormal cell growth in human breast cancer cells. In this study, we identified a novel regulatory mechanism of Wnt/β-catenin signaling through RARRES3 that targets and modulates the acylation status of Wnt proteins and co-receptor low-density lipoprotein receptor-related protein 6, resulting in the suppression of epithelial-mesenchymal transition and cancer stem cell properties. Mutation of the conserved active site residues of RARRES3 indicates that RARRES3 serves as an acyl protein thioesterase that tethers its target proteins and modulates their acylation status. Furthermore, the functions of p53 in cell proliferation and Wnt/β-catenin signaling are significantly associated with the induction of RARRES3. Thus our findings provide a new insight into the molecular link between p53, protein acylation and Wnt/β-catenin signaling whereby RARRES3 plays a pivotal role in modulating the acylation status of signaling proteins.

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.

Triptolide Transcriptionally Represses HER2 in Ovarian Cancer Cells by Targeting NF-κB

Triptolide (TPL) inhibits the proliferation of a variety of cancer cells and has been proposed as an effective anticancer agent. In this study, we demonstrate that TPL downregulates HER2 protein expression in oral, ovarian, and breast cancer cells. It suppresses HER2 protein expression in a dose- and time-dependent manner. Transrepression of HER2 promoter activity by TPL is also observed. The interacting site of TPL on the HER2 promoter region is located between −207 and −103 bps, which includes a putative binding site for the transcription factor NF-κB. Previous reports demonstrated that TPL suppresses NF-κB expression. We demonstrate that overexpression of NF-κB rescues TPL-mediated suppression of HER2 promoter activity and protein expression in NIH3T3 cells and ovarian cancer cells, respectively. In addition, TPL downregulates the activated (phosphorylated) forms of HER2, phosphoinositide-3 kinase (PI3K), and serine/threonine-specific protein kinase (Akt). TPL also inhibits tumor growth in a mouse model. Furthermore, TPL suppresses HER2 and Ki-67 expression in xenografted tumors based on an immunohistochemistry (IHC) assay. These findings suggest that TPL transrepresses HER2 and suppresses the downstream PI3K/Akt-signaling pathway. Our study reveals that TPL can inhibit tumor growth and thereby may serve as a potential chemotherapeutic agent.

Involvement of the prostaglandin D2 signal pathway in retinoid-inducible gene 1 (RIG1)-mediated suppression of cell invasion in testis cancer cells

Retinoid-inducible gene 1 (RIG1), also called tazarotene-induced gene 3, belongs to the HREV107 gene family, which contains five members in humans. RIG1 is expressed in high levels in well-differentiated tissues, but its expression is decreased in cancer tissues and cancer cell lines. We found RIG1 to be highly expressed in testicular cells. When RIG1 was expressed in NT2/D1 testicular cancer cells, neither cell death nor cell viability was affected. However, RIG1 significantly inhibited cell migration and invasion in NT2/D1 cells. We found that prostaglandin D2 synthase (PTGDS) interacted with RIG1 using yeast two-hybrid screens. Further, we found PTGDS to be co-localized with RIG1 in NT2/D1 testis cells. In RIG1-expressing cells, elevated levels of prostaglandin D2 (PGD2), cAMP, and SRY-related high-mobility group box 9 (SOX9) were observed. This indicated that RIG1 can enhance PTGDS activity. Silencing of PTGDS expression significantly decreased RIG1-mediated cAMP and PGD2 production. Furthermore, silencing of PTGDS or SOX9 alleviated RIG1-mediated suppression of migration and invasion. These results suggest that RIG1 will suppress cell migration/invasion through the PGD2 signaling pathway. In conclusion, RIG1 can interact with PTGDS to enhance its function and to further suppress NT2/D1 cell migration and invasion. Our study suggests that RIG1-PGD2 signaling might play an important role in cancer cell suppression in the testis.

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.

Endoplasmic reticulum stress is activated in endometrial adenocarcinoma

OBJECTIVES

Endometrial cancer is the most common malignancy of the female genital tract. However, in spite of a huge advance in our understanding of endometrial cancer biology, therapeutic modalities haven't significantly changed over the past 40 years. The activation of the Unfolded Protein Response (UPR) and GRP78 increase following Endoplasmic Reticulum (ER) stress have been recently identified as mechanisms favoring growth, invasion and resistance to therapy of different types of cancer. However, a possible role of ER stress and GRP78 in endometrial cancer has never been investigated.

METHODS

Tissue specimens from normal and neoplastic endometrium were analyzed for the expression of the ER stress markers GRP78, ATF6 and CHOP by Real-Time RT-PCR. In addition, GRP78 protein expression and localization were evaluated by Western blot and immunohistochemistry, respectively. The effect of GRP78 knock down on cell growth of Ishikawa cells was analyzed by proliferation curve analysis.

RESULTS

In this analysis, the expression levels of GRP78, ATF6 and CHOP mRNAs were significantly increased in specimens of endometrioid endometrial carcinomas. GRP78 and ATF6 protein expression levels were also increased in specimens of endometrial adenocarcinomas. GRP78 knock down caused a decrease of Ishikawa cells' growth.

CONCLUSIONS

The increased expression of ER stress markers in endometrioid endometrial carcinomas suggests a role for ER stress, the UPR and, possibly, GRP78 in endometrial cancer. Whether these mechanisms have a substantial function in the pathogenesis of malignant transformation of human endometrium is still under investigation in our laboratory.

A positive feedback loop between HER2 and ADAM12 in human head and neck cancer cells increases migration and invasion

Increased activation of epidermal growth factor receptor (EGFR) family members such as HER2/Erbb2 can result in more aggressive disease, resistance to chemotherapy and reduced survival of head and neck squamous cell carcinoma (HNSCC) patients. In order to identify mechanisms through which these receptor tyrosine kinases accelerate tumor progression, the regulation of metalloprotease expression by EGFR family members was investigated in 11 SCC cell lines. HER2 expression was significantly correlated with ADAM12 (A Disintegrin And Metalloprotease 12) expression in these cell lines and was co-expressed in human head and neck cancers. Inhibition of HER2 or EGFR decreased ADAM12 transcripts while HER2 transfection up-regulated ADAM12 expression. To understand the molecular mechanisms underlying HER2 regulation of ADAM12, we investigated the signaling pathways directing ADAM12 production in SCC cells. Inhibition of phosphatidyl inositol-3-kinase (PI3K) or mammalian Target of Rapamycin (mTOR) decreased ADAM12 transcripts in HER2-expressing SCC cells, while transfection with AKT increased ADAM12 mRNA. Experiments utilizing ADAM12 transfection or siRNA targeting of ADAM12 revealed that the protease increased both the migration and invasiveness of oral SCC cells. Surprisingly, ADAM12 also increased HER2 message, protein levels, and activity through an Ets1-dependent mechanism. Collectively, these results reveal a novel positive activation loop between ADAM12 and HER2 that may contribute to HNSCC progression.

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.

Magnolol down-regulates HER2 gene expression, leading to inhibition of HER2-mediated metastatic potential in ovarian cancer cells

Overexpression of the HER2 oncogene contributes to tumor cell invasion, metastasis and angiogenesis and correlates with poor prognosis. Magnolol has been reported to exhibit anti-tumor activities. However, the molecular mechanism of action of magnolol has not been investigated in HER2-positive cancer cells. Therefore, we examined the anti-cancer effects of magnolol on HER2-overexpressing ovarian cancer cells. Magnolol treatment caused a dose-dependent inhibition of HER2 gene expression at the transcriptional level, potentially in part through suppression of NF-κB activation. Treatment of HER2-overexpressing ovarian cancer cells with magnolol down-regulated the HER2 downstream PI3K/Akt signaling pathway, and suppressed the expression of downstream target genes, vascular endothelial growth factor (VEGF), matrix metalloproteinase 2 (MMP2) and cyclin D1. Consistently, magnolol-mediated inhibition of MMP2 activity could be prevented by co-treatment with epidermal growth factor. Migration assays revealed that magnolol treatment markedly reduced the motility of HER2-overexpressing ovarian cancer cells. Furthermore, magnolol-induced apoptosis in HER2-overexpressing ovarian cancer cells was characterized by the up-regulation of cleaved poly(ADP-ribose) polymerase (PARP) and activated caspase 3. These findings suggest that magnolol may act against HER2 and its downstream PI3K/Akt/mTOR-signaling network, thus resulting in suppression of HER2-mediated transformation and metastatic potential in HER2-overexpressing ovarian cancers. These results provide a novel mechanism to explain the anti-cancer effect of magnolol.

Toll-like receptor, RIG-I-like receptors and the NLRP3 inflammasome: key modulators of innate immune responses to double-stranded RNA viruses

Double-stranded RNA (dsRNA), the genetic material for many RNA viruses, induces robust host immune responses via pattern recognition receptors, which include Toll-like receptor 3 (TLR3), retinoic acid-inducible gene-I-like receptors (RLRs) and the multi-protein NLRP3 inflammasome complex. The engagement of dsRNA receptors or inflammasome activation by viral dsRNA initiates complex intracellular signaling cascades that play essential roles in inflammation and innate immune responses, as well as the resultant development of adaptive immunity. This review focuses on signaling pathways mediated by TLR3, RLRs and the NLRP3 inflammasome, as well as the potential use of agonists and antagonists that target these pathways to treat disease.

Gedunin, a novel natural substance, inhibits ovarian cancer cell proliferation

The discovery of more active therapeutic compounds is essential if the outcome for patients with advanced-stage epithelial ovarian cancer is to be improved. Gedunin, an extract of the neem tree, has been used as a natural remedy for centuries in Asia. Recently, gedunin has been shown to have potential in vitro antineoplastic properties; however, its effect on ovarian cancer cells is unknown. We evaluated the in vitro effect of gedunin on SKOV3, OVCAR4, and OVCAR8 ovarian cancer cell lines proliferation, alone and in the presence of cisplatin. Furthermore, we analyzed in vitro gedunin sensitivity data, integrated with genome-wide expression data from 54 cancer cell lines in an effort to identify genes and molecular pathways that underlie the mechanism of gedunin action. In vitro treatment of ovarian cancer cell lines with gedunin alone produced up to an 80% decrease in cell proliferation (P < 0.01) and, combining gedunin with cisplatin, demonstrated up to a 47% (P < 0.01) decrease in cell proliferation compared with cisplatin treatment alone. Bioinformatic analysis of integrated gedunin sensitivity and gene expression data identified 52 genes to be associated with gedunin sensitivity. These genes are involved in molecular functions related to cell cycle control, carcinogenesis, lipid metabolism, and molecular transportation. We conclude that gedunin has in vitro activity against ovarian cancer cells and, further, may enhance the antiproliferative effect of cisplatin. The molecular determinants of in vitro gedunin response are complex and may include modulation of cell survival and apoptosis pathways.

Expression, purification and biochemical characterization of the N-terminal regions of human TIG3 and HRASLS3 proteins

Tarzarotene-induced gene 3 (TIG3) and HRAS-like suppressor (HRASLS3) are members of the HREV107 family of class II tumor suppressors, which are down-regulated in various cancer cells. TIG3 and HRASLS3 also exhibit phospholipase activities. Both proteins share a common domain architecture with hydrophilic N-terminal and hydrophobic C-terminal regions. The hydrophobic C-terminal region is important for tumor suppression. However, the function of the hydrophilic N-terminal region remains elusive. To facilitate biochemical characterizations of TIG3 and HRASLS3, we expressed and purified the N-terminal regions of TIG3 and HRASLS3, designated TIG3 (1-134) and HRASLS3 (1-133), in a bacterial system. We found that the N-terminal regions of TIG3 and HRASLS3 have calcium-independent phospholipase A(2) activities. Limited proteolysis revealed that TIG3 (1-132) is a structural domain in the N-terminal region of TIG3. Our data suggest that the hydrophobic C-terminal regions might be crucial for cellular localization, while the hydrophilic N-terminal regions are sufficient for the enzymatic activity of both TIG3 and HRASLS3.

A reduction in Pten tumor suppressor activity promotes ErbB-2-induced mouse prostate adenocarcinoma formation through the activation of signaling cascades downstream of PDK1

Loss of function at the Pten tumor-suppressor locus is a common genetic modification found in human prostate cancer. While recent in vivo and in vitro data support an important role of aberrant ErbB-2 signaling to clinically relevant prostate target genes, such as cyclin D1, the role of Pten in ErbB-2-induced prostate epithelial proliferation is not well understood. In the Pten-deficient prostate cancer cell line, LNCaP, restoration of Pten was able to inhibit ErbB-2- and heregulin-induced cell cycle progression, as well as cyclin D1 protein levels and promoter activity. Previously, we established that probasin-driven ErbB-2 transgenic mice presented with high-grade prostate intraepithelial neoplasia and increased nuclear cyclin D1 levels. We show that mono-allelic loss of pten in the probasin-driven-ErbB-2 model resulted in increased nuclear cyclin D1 and proliferating cell nuclear antigen levels and decreased disease latency compared to either individual genetic model and, unlike the probasin-driven-ErbB-2 mice, progression to adenocarcinoma. Activated 3-phosphoinositide-dependent protein kinase-1 was observed during cancer initiation combined with the activation of p70S6K (phospho-T389) and inactivation of the 4E-binding protein-1 (phosphorylated on T37/46) and was primarily restricted to those cases of prostate cancer that had progressed to adenocarcinoma. Activation of mTOR was not seen. Our data demonstrates that Pten functions downstream of ErbB-2 to restrict prostate epithelial transformation by blocking full activation of the PDK1 signaling cascade.

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.