Differentiate or die: the view from Montreal

Evaluation of polyamines as marker of melanoma cell proliferation and differentiation by an improved high-performance liquid chromatographic method

The differentiation therapy is focused on the identification of new agents able to impair the proliferative and metastatic potential of cancer cells through the induction of differentiation. Although several markers of cell differentiation on tumor cells have been identified, their causal relationship with neoplastic competence has not been characterized in sufficient detail to propose their use as new pharmacological targets useful for the design of new differentiation agents. Polyamine level in cancer cells and in body fluids was proposed as potential marker of cell proliferation and differentiation. The main advantage of this marker is the possibility to evaluate the antineoplastic activity of new drugs able to induce cell differentiation and consequently to inhibit tumor growth and metastasis. The presented report shows a simply and highly reproducible reverse-phase high-performance liquid chromatographic (HPLC) method for the determination of ortho-phthalaldehyde (OPA) derivatives of polyamines: putrescine (PUT), cadaverine (CAD), spermidine (SPD) and spermine (SPM). The novelty of this method is the fluorescence response for OPA-derivate of SPM, generally low in other procedures, that has been significantly improved by the use of a fully endcapped packing material with minimal silanol interactions. The limits of detection for PUT, CAD, SPD and SPM were 0.6, 0.7, 0.8, and 0.4 pmol/mL, respectively. The analysis time was ≤ 20 min, and the relative recovery rate was of about 97%. To verify the usefulness of this method, it has been validated in a murine melanoma cell line (B16-F10) treated with two theophylline derivatives (namely 8-chlorotheophylline and 8-bromotheophylline). These two compounds increased the activity of tissue transglutaminase (TG2) and the synthesis of melanin, two recognized markers of melanoma cell differentiation, and significantly reduced the levels of intracellular polyamines.

Transglutaminases: future perspectives

This is the third special issue focused on "Transglutaminases" that is now available on this journal and dedicated to one of the pioneers of these enzymes, John Edward Folk, who died December 2010 [see in this issue Beninati et al. 2012a]. The first edition, "Polyamines and Transglutaminases" was published in Amino Acids, vol 26, no. 4, 2004, with the contribution of two prestigious Guest Editors as Alberto Abbruzzese and Mauro Piacentini. This editorial initiative was followed by the second special issue published in occasion of the 50th years of the discovery of transglutaminase. Indeed, "Transglutaminase 2: 50th Anniversary of the Discovery" Amino Acids, vol 36, no. 4, 2009, was published with the valuable collaboration of Carlo Maria Bergamini and Mauro Piacentini (Beninati et al. 2009). To continue with this editorial tradition, on this occasion, an outstanding board of Guest Editors composed by Francesco Facchiano and Mauro Piacentini has also been invited to promote this initiative and recruit a selected panel of Authors, many of who participated in the first and second edition of the Gordon Conference on Transglutaminases: "Transglutaminases in Human Diseases Processes" chaired by Rickard L Eckert and Kapil Mehta on July 18-23, 2010, and by Kapil Mehta and Mauro Piacentini on July 15-20, 2012, held at Davidson College, NC, USA. In this Amino Acids special issue, the manuscripts were selected to reflect the progress and the future perspectives of transglutaminases.

Synergic effect of α-tocopherol and naringenin in transglutaminase-induced differentiation of human prostate cancer cells

Prostate cancer is the second most common cancer in men worldwide. Its prevention and treatment remain a challenge to clinicians. Thus, there is an urgent need to discover novel, less toxic, and more effective therapies for patients. Many vitamins and related chemicals, including vitamin E, (tocopherols) have shown their anti-cancer activities as anti-oxidants, activators of transcription factors or factors influencing epigenetic events. Although laboratory tests including the use of animal models showed that this vitamin may have anticancer properties, whether it can effectively prevent the development and/or progression of prostate cancer in humans remains to be intensively studied. This review provides up-to-date information regarding the recent outcomes of laboratory, epidemiology and/or clinical trials on the effects of tocopherols on prostate cancer development, along with our last observations on a combined treatment of a prostate cancer cell line (PC-3) with two natural antineoplastic compounds, naringenin (NG) and α-tocopherol (α-TOC). We report the synergic effect of α-TOC and NG in transglutaminase-induced differentiation of human PC-3 prostate cancer cells. While our results are based on one histological class of tumor, the most significant implication of this observation is that establishes a new way in the screening for detecting new differentiative antineoplastic agents.

Similar antineoplastic effects of nimesulide, a selective COX-2 inhibitor, and prostaglandin E1 on B16-F10 murine melanoma cells

There is now increasing evidence that a constitutive expression of cyclooxygenase 2 (COX-2) plays a role in the development and progression of malignant ectodermal tumours. In this study, we investigated whether the selective inhibition of COX-2 would be beneficial in melanoma treatment. Nimesulide, a selective inhibitor of COX-2 that causes the breakdown of proinflammatory 2-series prostaglandins (PG2), adversely affected the growth of B16-F10 melanoma cells through the induction of differentiation. The intracellular levels of polyamine, as a proliferation marker, were reduced by the treatment; at the same time, transglutaminase activation and increase in melanin content, as differentiation indicators, were observed. The potential antimetastatic activity of the drug was further shown by means of the Boyden invasion assay and gelatin zymography for metalloproteinase activity. Comparable results were obtained after the treatment of cells with one of the 1-series PGs (PGE1). Therefore, our hypothesis is that the antineoplastic activity observed for nimesulide may be ascribed to intracellular changes in alterations in PG levels.

Antitumor properties of aloe-emodin and induction of transglutaminase 2 activity in B16-F10 melanoma cells

AIMS

Aloe-emodin (AE), a natural hydroxyanthraquinone compound, has been reported as a potential anticancer agent. We studied the antineoplastic properties of AE on highly metastatic B16-F10 melanoma murine cells.

MAIN METHODS

Cell proliferation was assessed by cell counting and viability was investigated using MTT and Trypan Bleu exclusion tests. As a growth marker, we determined intracellular polyamine levels by high performance liquid chromatography. Then, we evaluated transglutaminase 2 (TG2) activity, protoporphyrin IX accumulation and melanin content as differentiative markers. Tyrosinase activity was checked by DOPA-staining assay. The antimetastatic effect of AE was evaluated by means of a series of in vitro metastatic assays, including aggregation, wound healing migration, adhesion, 3D-invasion, circular invasion and the Boyden chamber invasion assays. Gelatin zymography was performed to evaluate metalloproteinase activities.

KEY FINDINGS

Our results demonstrated inhibitory effects of AE on melanoma cell proliferation and invasion power, accompanied by the stimulation of cell differentiation parameters. Cell differentiation correlated with a remarkable increase of the activity of the transamidating form of TG2, with a significative enhancement of cell adhesion and aggregation. Impaired invasion was paralleled by the decrease of the secretion of matrix metalloproteinase-9.

SIGNIFICANCE

The overall data confirm a remarkable antiproliferative, antimetastatic and differentiative capability of this anthraquinone. Results suggest that AE appears particularly promising for its potential application in the newborn differentiation therapy of cancer.

Phytochemicals and protein-polyamine conjugates by transglutaminase as chemopreventive and chemotherapeutic tools in cancer

Identifying novel chemopreventive and chemotherapeutic agents and targeting them to patients at high risk of developing cancer or following curative treatment may go some way towards improving prognosis. This review examines current knowledge regarding the chemopreventive and chemotherapeutic potential of phytochemicals in cancer. Both in vitro and animal studies demonstrate that several phytochemicals increase the activity of intracellular transglutaminases, a family of enzymes involved in cell differentiation, through the covalent conjugation of polyamine to cellular protein, with promising anti-neoplastic properties. The substantial data available on certain plant secondary metabolites makes a strong case for integrating these safe and well-tolerated agents into clinical practice.

Role of transglutaminase 2 in quercetin-induced differentiation of B16-F10 murine melanoma cells

Flavonoids belong to the class of plant polyphenolic compounds with over 6,000 individual structures known. These phytochemicals have attracted the interest of the scientists, because they possess a remarkable spectrum of biological activities, such as antiallergic, antiinflammatory, antioxidant, antimutagenic and anticarcinogenic. In this work, we compared the anticancer potential of two flavonoids, quercetin and pelargonidin, on highly metastatic B16-F10 melanoma murine cells. We have evaluated different parameters related to cell proliferation and differentiation, such as cell number, toxicity, intracellular content of polyamines and transglutaminase (TG, EC 2.3.2.13) activity. The higher inhibition of tumor cell growth, with respect to control, was obtained with quercetin cell treatment, i.e. 32% reduction after 48 h and 39% reduction after 72 h of incubation (P < 0.001). In parallel, quercetin-treated cells showed a similar decrease in polyamine content. TG activity was fourfold increased, with respect to control, after 48 h and twofold increased after 72 h (P < 0.001). Pelargonidin treatment did not show significant antiproliferative effects and any increase in TG activity. Proteomic approach was used to investigate changes in protein expression profiles in tumor cells following quercetin treatment. Changes in expression of 60 proteins were detected, i.e. 8 proteins were down-regulated, 35 up-regulated, 11 "de novo" synthetized proteins and 6 suppressed proteins were present in treated cells. A 80 kDa spot, identified as TG type 2 by Western blot analysis, presented a fourfold increase in intensity, confirming the key role played by TG in the induction of cancer cell differentiation.

Basic helix-loop-helix proteins bind to TrkB and p21(Cip1) promoters linking differentiation and cell cycle arrest in neuroblastoma cells

Differentiation of precursor into specialized cells involves an increasing restriction in proliferative capacity, culminating in cell cycle exit. In this report we used a human neuroblastoma cell line to study the molecular mechanisms that coordinate cell cycle arrest and neuronal differentiation. Exposure to retinoic acid (RA), a differentiation agent in many cell types, causes an upregulation of neurotrophin receptor TrkB and the cyclin kinase inhibitor p21(Cip1) at a transcriptional level. Full transcriptional activation of these two genes requires canonical E-box sequences found in the TrkB and p21(Cip1) promoters. As reported for other E-box-regulated promoters, ectopic expression of E47 and E12 basic helix-loop-helix (bHLH) proteins enhances RA-dependent expression of TrkB and p21(Cip1), whereas the inhibitory HLH Id2 exerts opposite effects. In addition, ectopic expression of E47 and NeuroD, a neuronal bHLH protein, is able to activate TrkB transcription in the absence of RA. More importantly, we show that E47 and NeuroD proteins bind the TrkB and p21(Cip1) promoter sequences in vivo. Since they establish a direct transcriptional link between a cell cycle inhibitor, p21(Cip1), and a neurotrophic receptor, TrkB, bHLH proteins would play an important role in coordinating key events of cell cycle arrest and neuronal differentiation.