Retinoic acid receptors and tissue-transglutaminase mediate short-term effect of retinoic acid on migration and invasion of neuroblastoma SH-SY5Y cells

Retinoic acid reduces human neuroblastoma cell migration and invasiveness: effects on DCX, LIS1, neurofilaments-68 and vimentin expression

BACKGROUND

Neuroblastoma is a severe pediatric tumor, histologically characterised by a variety of cellular phenotypes. One of the pharmacological approaches to neuroblastoma is the treatment with retinoic acid. The mechanism of action of retinoic acid is still unclear, and the development of resistance to this differentiating agent is a great therapy problem.Doublecortin, a microtubule-associated protein involved in neuronal migration, has recently been proposed as a molecular marker for the detection of minimal residual disease in human neuroblastoma. Nevertheless, no information is available on the expression of doublecortin in the different cell-types composing human neuroblastoma, its correlation with neuroblastoma cell motility and invasiveness, and the possible modulations exerted by retinoic acid treatment.

METHODS

We analysed by immunofluorescence and by Western blot analysis the presence of doublecortin, lissencephaly-1 (another protein involved in neuronal migration) and of two intermediate filaments proteins, vimentin and neurofilament-68, in SK-N-SH human neuroblastoma cell line both in control conditions and under retinoic acid treatment. Migration and cell invasiveness studies were performed by wound scratch test and a modified microchemotaxis assay, respectively.

RESULTS

Doublecortin is expressed in two cell subtypes considered to be the more aggressive and that show high migration capability and invasiveness. Vimentin expression is excluded by these cells, while lissencephaly-1 and neurofilaments-68 are immunodetected in all the cell subtypes of the SK-N-SH cell line. Treatment with retinoic acid reduces cell migration and invasiveness, down regulates doublecortin and lissencephaly-1 expression and up regulates neurofilament-68 expression. However, some cells that escape from retinoic acid action maintain migration capability and invasiveness and express doublecortin.

CONCLUSION

a) Doublecortin is expressed in human neuroblastoma cells that show high motility and invasiveness;b) Retinoic acid treatment reduces migration and invasiveness of the more aggressive cell components of SK-N-SH cells;c) The cells that after retinoic acid exposure show migration and invasive capability may be identified on the basis of doublecortin expression.

Overexpression of tissue transglutaminase leads to constitutive activation of nuclear factor-kappaB in cancer cells: delineation of a novel pathway

The transcription factor nuclear factor-kappaB (NF-kappaB) plays an important role in regulating cell growth, apoptosis, and metastatic functions. Constitutive activation of NF-kappaB has been observed in various cancers; however, molecular mechanisms resulting in such activation remain elusive. Based on our previous results showing that drug-resistant and metastatic cancer cells have high levels of tissue transglutaminase (TG2) expression and that this expression can confer chemoresistance to certain types of cancer cells, we hypothesized that TG2 contributes to constitutive activation of NF-kappaB. Numerous lines of evidence showed that overexpression of TG2 is linked with constitutive activation of NF-kappaB. Tumor cells with overexpression of TG2 exhibited increased levels of constitutively active NF-kappaB. Activation of TG2 led to activation of NF-kappaB; conversely, inhibition of TG2 activity inhibited activation of NF-kappaB. Similarly, ectopic expression of TG2 caused activation of NF-kappaB, and inhibition of expression of TG2 by small interfering RNA abolished the activation of NF-kappaB. Our results further indicated that constitutive NF-kappaB reporter activity in pancreatic cancer cells is not affected by dominant-negative I kappaB alpha. Additionally, coimmunoprecipitation and confocal microscopy showed that I kappaB alpha is physically associated with TG2. Lastly, immunohistochemical analysis of pancreatic ductal carcinoma samples obtained from 61 patients further supported a strong correlation between TG2 expression and NF-kappaB activation/overexpression (P = 0.0098, Fisher's exact test). We conclude that TG2 induces constitutive activation of NF-kappaB in tumor cells via a novel pathway that is most likely independent of I kappaB alpha kinase. Therefore, TG2 may be an attractive alternate target for inhibiting constitutive NF-kappaB activation and rendering cancer cells sensitive to anticancer therapies.

Tissue transglutaminase induces the release of apoptosis inducing factor and results in apoptotic death of pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignant disease with poor long-term survival rates. Major reason for poor disease outcome is the profound intrinsic resistance of PDAC cells to currently available treatment regimens. We recently found that a great majority of PDAC tumors and tumor cell lines express high basal level of tissue transglutaminase (TG2), a multifunctional protein implicated in apoptosis, cell attachment, cell survival, and cell motility functions. Based on these observations, we hypothesized that activation of endogenous TG2 can induce spontaneous apoptosis in PDAC cells. The results obtained suggested that activation of endogenous TG2 by calcium ionophore A23187 induced rapid and spontaneous apoptosis in PDAC cells. TG2-induced apoptosis was associated with release of apoptosis-inducing factor (AIF). The release of AIF from mitochondria led to its translocation to the nucleus and subsequent apoptosis of PDAC cells in caspase-independent manner. In conclusion, our results provide first evidence that TG2 can induce apoptosis in PDAC cells in an AIF-dependent and caspase-independent manner.

Localized rbp4 expression in the yolk syncytial layer plays a role in yolk cell extension and early liver development

BACKGROUND

The number of genes characterized in liver development is steadily increasing, but the origin of liver precursor cells and the molecular control of liver formation remain poorly understood. Existing theories about formation of zebrafish visceral organs emphasize either their budding from the endodermal rod or formation of independent anlage followed by their later fusion, but none of these is completely satisfactory in explaining liver organogenesis in zebrafish.

RESULTS

Expression of a gene encoding the retinol binding protein 4 (Rbp4) was analyzed in zebrafish. rbp4, which is expressed mainly in the liver in adults, was shown to be expressed in the yolk syncytial layer (YSL) during early embryogenesis. At 12-16 hpf rbp4 expression was restricted to the ventro-lateral YSL and later expanded to cover the posterior YSL. We demonstrated that rbp4 expression was negatively regulated by Nodal and Hedgehog (Hh) signalling and positively controlled by retinoic acid (RA). Knockdown of Rbp4 in the YSL resulted in shortened yolk extension as well as the formation of two liver buds, which could be due to impaired migration of liver progenitor cells. rbp4 appears also to regulate the extracellular matrix protein Fibronectin1 (Fn1) specifically in the ventro-lateral yolk, indicating a role of Fn1 in liver progenitor migration. Since exocrine pancreas, endocrine pancreas, intestine and heart developed normally in Rbp4 morphants, we suggest that rbp4 expression in the YSL is required only for liver development.

CONCLUSION

The characteristic expression pattern of rbp4 suggests that the YSL is patterned despite its syncytial nature. YSL-expressed Rbp4 plays a role in formation of both yolk extension and liver bud, the latter may also require migration of liver progenitor cells.

Hyaluronic acid induces transglutaminase II to enhance cell motility; role of Rac1 and FAK in the induction of transglutaminase II

The role of transglutaminase II (TGase II) in hyaluronic acid (HA)-promoted melanoma cell motility was investigated. HA induced the expression of TGase II via the nuclear factor kappaB (NF-kB) in melanoma cells. HA increased the Rac1 activity and phosphorylation of focal adhesion kinase (FAK). Transfection by lipofectamine of dominant-negative Rac1, and FAK-related non-kinase (FRNK), an endogenous inhibitor of FAK, suppressed the induction of TGase II. This suggests that Rac1 and FAK mediate induction of TGase II by HA. HA-promoted melanoma cell motility was inhibited by cystamine, an inhibitor of TGase II, and overexpression of TGase II enhanced melanoma cell motility through reactive oxygen species. Taken together, HA promotes melanoma cell motility through activation of Rac1, FAK, and induction of TGase II.

Heterogeneity in retinoic acid signaling in neuroblastomas: Role of matrix metalloproteinases in retinoic acid-induced differentiation

Causes of retinoid resistance often observed in neuroblastomas are unknown. We studied all trans-retinoic acid (RA) signaling in neuroblastoma cells differing in N-myc levels in terms of neurite formation, expression of tissue transglutaminase, neuronal marker proteins, matrix metalloproteinases (MMPs), and activation of Rac1 and Cdc42. Poor invasiveness observed in SH-SY5Y, LA-N-5, and SMS-KCNR cells was associated with RA-induced neurite formation, Cdc42 activation and N-myc down regulation; expression of constitutively active Cdc42 down regulated N-myc expression and reduced invasion in RA-resistant SK-N-BE(2) and IMR32 cells. RA treatment for 24 h transiently increased invasion and expression of MMP9 in SH-SY5Y, LA-N-5 and MMP2 in SMS-KCNR cells. MMP inhibition prevented RA-induced neurite formation indicating a role in differentiation. Variation in RA signaling thus follows a defined pattern and relates to invasive potential. A defective RA signaling might result in retinoid resistance and unpredictable clinical outcome observed in some neuroblastomas.

Knockdown of XAB2 Enhances All-Trans Retinoic Acid–Induced Cellular Differentiation in All-Trans Retinoic Acid–Sensitive and –Resistant Cancer Cells

Xeroderma pigmentosum group A (XPA)-binding protein 2 (XAB2) is composed of 855 amino acids, contains 15 tetratricopeptide repeat motifs, and associates with Cockayne syndrome group A and B proteins and RNA polymerase II, as well as XPA. In vitro and in vivo studies showed that XAB2 is involved in pre-mRNA splicing, transcription, and transcription-coupled DNA repair, leading to preimplantation lethality, and is essential for mouse embryogenesis. Retinoids are effective for the treatment of preneoplastic diseases including xeroderma pigmentosum and other dermatologic diseases such as photoaging. We therefore focused on defining the effect of XAB2 on cellular differentiation in the presence of ATRA treatment. In the present study, we showed that overexpression of XAB2 inhibited ATRA-induced cellular differentiation in human rhabdomyosarcoma cell line, and that knockdown of XAB2 by small interfering RNA (siRNA) increased ATRA-sensitive cellular differentiation in the human promyelocytic leukemia cell line HL60 at both physiologic (10(-9)-10(-8) mol/L) and therapeutic (10(-7) mol/L) concentrations of ATRA. Moreover, we found that XAB2 was associated with retinoic acid receptor alpha (RARalpha) and histone deacetylase 3 in the nuclei. Finally, using siRNA against XAB2, we showed that the ATRA-resistant neuroblastoma cell line IMR-32 underwent cellular differentiation induced by ATRA at a therapeutic concentration (10(-6) mol/L). These results strongly suggest that XAB2 is a component of the RAR corepressor complex with an inhibitory effect on ATRA-induced cellular differentiation and that XAB2 plays a role in ATRA-mediated cellular differentiation as an important aspect of cancer therapy.

Identification of the RA response element and transcriptional silencer in human alphaCaMKII promoter

The promoter of alpha subunit of the rat calcium/calmodulin-dependent protein kinase II (alphaCaMKII) gene was identified to contain an essential TATA element. Cell-based functional assay showed that the rat promoter displayed greater activity in neuronal cells than in non-neuronal cells. To characterize the human alphaCaMKII promoter, we have developed a promoter-reporter gene assay using different cell lines. A 2047 base pairs (bp) human alphaCaMKII gene promoter was cloned from human genomic DNA. Unlike the rat alphaCaMKII promoter, DNA sequence analysis showed that the human promoter was devoid of TATA element. We made series deletions of the promoter and fused the different sizes of the human promoter sequences to a luciferase reporter gene. The promoter-reporter constructs were transfected into human neuroblastoma SH-SY5Y, human neuroblastoma BE(2)-M17, and rat pheochromocytoma PC12 neuronal cell lines as well as human embryonic kidney HEK293 and human glioma U251 non-neuronal cell lines. The reporter gene assay demonstrated that the human alphaCaMKII promoter displayed high activity in the neuronal cell lines, while the activity was low in non-neuronal cell lines. All-trans retinoic acid (RA) enhanced the promoter activity in SH-SY5Y cells. Further analysis showed that there were two RA response elements located between +11 and +136 and -1911 to -593. In addition, we have identified a potent silencer at position -179 to -244 of the human alphaCaMKII promoter.

Cytodifferentiation by retinoids, a novel therapeutic option in oncology: rational combinations with other therapeutic agents

Retinoic acid (RA) and derivatives are promising antineoplastic agents endowed with both therapeutic and chemopreventive potential. Although the treatment of acute promyelocytic leukemia with all-trans retinoic acid is an outstanding example, the full potential of retinoids in oncology has not yet been explored and a more generalized use of these compounds is not yet a reality. One way to enhance the therapeutic and chemopreventive activity of RA and derivatives is to identify rational combinations between these compounds and other pharmacological agents. This is now possible given the information available on the biochemical and molecular mechanisms underlying the biological activity of retinoids. At the cellular level, the antileukemia and anticancer activity of retinoids is the result of three main actions, cytodifferentiation, growth inhibition, and apoptosis. Cytodifferentiation is a particularly attractive modality of treatment and differentiating agents promise to be less toxic and more specific than conventional chemotherapy. This is the result of the fact that cytotoxicity is not the primary aim of differentiation therapy. At the molecular level, retinoids act through the activation of nuclear retinoic acid receptor-dependent and -independent pathways. The cellular pathways and molecular networks relevant for retinoid activity are modulated by a panoply of other intracellular and extracellular pathways that may be targeted by known drugs and other experimental therapeutics. This chapter aims to summarize and critically discuss the available knowledge in the field.

Tissue transglutaminase expression promotes cell attachment, invasion and survival in breast cancer cells

Distant metastasis is frequently observed in patients with breast cancer and is a major cause of cancer-related deaths in these patients. Currently, very little is known about the mechanisms that underlie the development of the metastatic phenotype in breast cancer cells. We previously found that metastatic breast cancer cells express high levels of tissue transglutaminase (TG2), but established no direct link between TG2 and metastasis. In this study, we hypothesized that TG2 plays a role in conferring the metastatic phenotype to breast cancer cells. The results obtained suggested that increased expression of TG2 in breast cancer cells contributes to their increased survival, invasion and motility. We further found that TG2 protein in a metastatic breast cancer MDA-MB231 cells was present on the cell surface in close association with integrins beta1, beta4 and beta5. Downregulation of endogenous TG2 by small interfering RNA inhibited fibronectin (Fn)-mediated cell attachment, survival and invasion. Conversely, ectopic expression of TG2 augmented invasion of breast cancer cells and attachment to Fn-coated surfaces. We conclude that TG2 expression in breast cancer cells plays an important role in the development of the metastatic phenotype.