Transforming growth factor-β1 inhibits all-trans retinoic acid-induced apoptosis

Synthetic Diphenylacetylene-Based Retinoids Induce DNA Damage in Chinese Hamster Ovary Cells without Altering Viability

All-trans-retinoic acid (ATRA), the active metabolite of vitamin A, plays a pivotal role in cell differentiation, proliferation and embryonic development. It is an effective therapy for dermatological disorders and malignancies. ATRA is prone to isomerization and oxidation, which can affect its activity and selectivity. Novel diphenylacetylene-based ATRA analogues with increased stability can help to overcome these problems and may offer significant potential as therapeutics for a variety of cancers and neurodegenerative diseases, including amyotrophic lateral sclerosis. Here, we investigated the effects of these retinoids on cell viability and genotoxicity in the widely used model system of the rapidly proliferating Chinese hamster ovary cell line. DC360 is a fluorescent ATRA analogue and DC324 is a non-active derivative of DC360. EC23, DC525, DC540, DC645, and DC712 are promising analogues with increased bioactivity. The cytotoxic activity of the compounds was evaluated by ATP assay and DNA damage was tested by comet assay. No cytotoxicity was observed in the 10⁻⁶–10⁻⁵ M concentration range. All compounds induced DNA migration similar to ATRA, but DC324, DC360 and EC23 did so to a greater extent, particularly at higher concentrations. We believe that retinoid receptor-independent genotoxicity is a general characteristic of these compounds; however, further studies are needed to identify the molecular mechanisms and understand their complex biological functions.

Loss of TG-Interacting Factor 1 decreases survival in mouse models of myeloid leukaemia

TG‐Interacting Factor 1 (Tgif1) affects proliferation and differentiation of myeloid cells and regulates self‐renewal of haematopoietic stem cells (HSCs). To determine its impact on leukaemic haematopoiesis, we induced acute or chronic myeloid leukaemias (AML or CML) in mice by enforced expression of MLL‐AF9 or BCR‐ABL, respectively, in Tgif1^+/+ or Tgif1^−/− haematopoietic stem and progenitor cells (HSPCs) and transplanted them into syngeneic recipients. We find that loss of Tgif1 accelerates leukaemic progression and shortens survival in mice with either AML or CML. Leukaemia‐initiating cells (LICs) occur with higher frequency in AML among mice transplanted with MLL‐AF9‐transduced Tgif1^−/− HSPCs than with Tgif1^+/+ BMCs. Moreover, AML in mice generated with Tgif1^−/− HSPCs are chemotherapy resistant and relapse more rapidly than those whose AML arose in Tgif1^+/+ HSPCs. Whole transcriptome analysis shows significant alterations in gene expression profiles associated with transforming growth factor‐beta (TGF‐beta) and retinoic acid (RA) signalling pathways because of Tgif1 loss. These findings indicate that Tgif1 has a protective role in myeloid leukaemia initiation and progression, and its anti‐leukaemic contributions are connected to TGF‐beta‐ and RA‐driven functions.

12-O-Tetradecanoylphorbol-13-acetate increases cardiomyogenesis through PKC/ERK signaling

12-O-Tetradecanoylphorbol-13-acetate (TPA) is the most widely used diacylglycerol (DAG) mimetic agent and inducer of protein kinase C (PKC)-mediated cellular response in biomedical studies. TPA has been proposed as a pluripotent cell differentiation factor, but results obtained have been inconsistent. In the present study we show that TPA can be applied as a cardiomyogenesis-promoting factor for the differentiation of mouse embryonic stem (mES) cells in vitro. The mechanism of TPA action is mediated by the induction of extracellular signal-regulated kinase (ERK) activity and the subsequent phosphorylation of GATA4 transcription factor. Interestingly, general mitogens (FGF, EGF, VEGF and serum) or canonical WNT signalling did not mimic the effect of TPA. Moreover, on the basis of our results, we postulate that a TPA-sensitive population of cardiac progenitor cells exists at a certain time point (after days 6–8 of the differentiation protocol) and that the proposed treatment can be used to increase the multiplication of ES cell-derived cardiomyocytes.

Negative control of TRAIL-R1 signaling by transforming growth factor β1 in pancreatic tumor cells involves Smad-dependent down regulation of TRAIL-R1

Pancreatic ductal adenocarcinoma (PDAC) is characterized by both, overexpression of transforming growth factor (TGF)β and resistance of the tumor cells to many apoptosis-inducing stimuli. The latter negatively impacts the outcome of therapeutic efforts and represents one important mechanism which tumor cells utilize to escape the immune surveillance. Since TGFβ acts as a tumor promoter in advanced tumor stages and suppression of apoptosis is a known driver of tumor progression, it is possible that TGFβ functions as a crucial determinant of tumor cell sensitivity to apoptosis in PDAC. Here, we have studied the impact of TGFβ on TNF-related apoptosis inducing ligand (TRAIL)-induced signaling in PDAC cells. In TGFβ-responsive Panc1 and Colo357 cells, TGFβ1 reduced total and plasma membrane-associated levels of TRAIL-R1 but not those of TRAIL-R2. Consistent with the known predominant role of TRAIL-R1 in TRAIL-mediated signaling in PDAC, TGFβ1 inhibited TRAIL-induced DISC formation and apoptosis as well as phosphorylation of MAPKs and IκBα. Similarly, it also reduced signaling of TRAIL-R1 following its specific activation with an agonistic antibody. In contrast, specific TRAIL-R2 signaling remained unchanged. The TGFβ1 effect on TRAIL-R1 expression was mimicked by ectopic expression of a kinase-active version of the TGFβ type I receptor ALK5 (ALK5-T204D) but not by ALK5 double mutant lacking the ability to phosphorylate Smad proteins (RImL45-T204D). Moreover, TGFβ regulation of TRAIL-R1 was absent in two PDAC cell lines lacking the Smad4 gene DPC4 and siRNA-mediated silencing of Smad4 in Smad4-positive Panc1 cells abolished the TGFβ-mediated decrease in TRAIL-R1 expression, together showing that ALK5/Smad4 signaling is crucial for TGFβ regulation of TRAIL-R1 expression. Our results suggest a novel tumor-promoting function of TGFβ1. By downregulating TRAIL-R1, TGFβ1 may not only promote tumor escape from immune surveillance but also negatively impact on TRAIL- or TRAIL-R1-based therapy regimens for treatment of PDAC.

DNA fragmentation induced by all-trans retinoic acid and its steroidal analogue EA-4 in C2 C12 mouse and HL-60 human leukemic cells in vitro

We have recently shown that retinoic acid induces micronucleation mainly via chromosome breakage (Alakhras et al. Cancer Lett 2011; 306: 15-26). To further study retinoic acid clastogenicity and evaluate DNA damaging potential we investigated the ability of (a) all-trans retinoic acid and its steroidal analogue EA-4 to induce DNA fragmentation by using Comet assay under alkaline unwinding and neutral condition electrophoresis, and (b) the retinoids under study to induce small (0-1 kb) DNA fragments. Two cell lines, C2C12 mouse cells and HL-60 human leukemic cells were used in this study. We found that all-trans retinoic acid and its steroidal analogue EA-4 (a) provoke DNA migration due to DNA fragmentation as it is shown by the increased values of Comet parameters, and (b) induce significantly small-size fragmented genomic DNA as indicated by the quantification of necrotic/apoptotic small DNA segments in both cell systems. A different response between the two cell lines was observed in relation to retinoid ability to increase the percentage of DNA in the tail as well as break DNA in to small fragments. Our findings confirm the ability of retinoic acid to provoke micronucleation by disrupting DNA into fragments, among which small pieces of double-stranded DNA up to 1 kb are identified.

Retinoid and TGF-β families: crosstalk in development, neoplasia, immunity, and tissue repair

Transforming growth factor-β (TGF-β) isoforms are profibrotic cytokines, par excellence, and have complex multifunctional effects on many systems, depending on the biologic setting. Retinoids are vitamin A derivatives that also have diverse effects in development, physiology, and disease. The interactions between these classes of molecules are, not surprisingly, highly complex and are dependent on the tissue, cellular, and molecular settings.

TRAIL and vitamins: opting for keys to castle of cancer proteome instead of open sesame

Cancer is a multifaceted molecular disorder that is modulated by a combination of genetic, metabolic and signal transduction aberrations, which severely impair the normal homeostasis of cell growth and death. Accumulating findings highlight the fact that different genetic alterations, such as mutations in tumor suppressor genes, might be related to distinct and differential sensitivity to targeted therapies. It is becoming increasingly apparent that a multipronged approach that addresses genetic milieu (alterations in upstream and/or parallel pathways) eventually determines the response of individual tumors to therapy. Cancerous cells often acquire the ability to evade death by attenuating cell death pathways that normally function to eliminate damaged and harmful cells. Therefore impaired cell death nanomachinery and withdrawal of death receptors from cell surface are some of major determinants for the development of chemotherapeutic resistance encountered during treatment. It is therefore essential to emphasize underlying factors which predispose cells to refractoriness against TRAIL mediated cell death pathway and the relevant regulatory components involved. We bring to limelight the strategies to re-sensitize TRAIL resistant cells via vitamins to induce apoptosis.

TGF-β(1) in retinal ganglion cells in rats with chronic ocular hypertension: its expression and anti-apoptotic effect

AIM

To investigate the anti-apoptotic effect of transforming growth factor beta-1 (TGF-β(1)) on chronic ocular hypertension.

METHODS

The expression of TGF-β(1) in retinal ganglion cells (RCGs) was measured using the immunohistochemiscal S-P method and real-time PCR in the normally control group, the ocular hypertension group (experimental group A), the ocular hypertension plus antibody intervention group (experimental group B) and the ocular hypertension plus antigen intervention group (experimental group C) at 1, 2, 3 and 4 weeks postoperatively. The count of apoptotic RCGs was measured using the TUNEL method.

RESULTS

The expression of TGF-β(1 )was significantly higher in experimental group C than that in other three groups (P<0.05). The expression was the lowest in experimental group B (4.17%). A statistically significant difference was noted between the four groups (P<0.01). The count of apoptotic RCGs was statistically significantly lower in experimental group C than that in the experimental groups A and B (P<0.01). A statistically significant difference was noted in the count of apoptotic RCGs between these three experimental groups (P<0.01).

CONCLUSION

TGF-β(1) can inhibit the apoptosis of RCGs in rats with chronic ocular hypertension.

ABC transporters affect the detection of intracellular oxidants by fluorescent probes

Intracellular production of reactive oxygen species (ROS) plays an important role in the control of cell physiology. For the assessment of intracellular ROS production, a plethora of fluorescent probes is commonly used. Interestingly, chemical structures of these probes imply they could be substrates of plasma membrane efflux pumps, called ABC transporters. This study tested whether the determination of intracellular ROS production and mitochondrial membrane potential by selected fluorescent probes is modulated by the expression and activity of ABC transporters. The sub-clones of the HL-60 cell line over-expressing MDR1, MRP1 and BCRP transporters were employed. ROS production measured by luminol- and L-012-enhaced chemiluminescence and cytochrome c reduction assay showed similar levels of ROS production in all the employed cell lines. It was proved that dihydrorhodamine 123, dihexiloxocarbocyanine iodide, hydroethidine, tetrachloro-tetraethylbenzimidazolocarbo-cyanine iodide and tetramethylrhodamine ethyl ester perchlorate are substrates for MDR1; dichlorodihydrofluoresceine, hydroethidine and tetramethylrhodamine ethyl ester perchlorate are substrates for MRP1; dichlorodihydrofluoresceine, dihydrorhodamine 123, hydroethidine and tetrachloro-tetraethylbenzimidazolocarbo-cyanine iodide are substrates for BCRP. Thus, the determination of intracellular ROS and mitochondrial potential by the selected probes is significantly altered by ABC transporter activities. The activity of these transporters must be considered when employing fluorescent probes for the assessment of ROS production or mitochondrial membrane potential.

Dynamic Monitoring of Cellular Remodeling Induced by the Transforming Growth Factor-β1

The plasticity of differentiated adult cells could have a great therapeutic potential, but at the same time, it is characteristic of progression of serious pathological states such as cancer and fibrosis. In this study, we report on the application of a real-time noninvasive system for dynamic monitoring of cellular plasticity. Analysis of the cell impedance profile recorded as cell index using a real-time cell analyzer revealed its significant increase after the treatment of prostate epithelial cells with the transforming growth factor-β1. Changes in the cell index profile were paralleled with cytoskeleton rebuilding and induction of epithelial–mesenchymal transition and negatively correlated with cell proliferation. This novel application of such approach demonstrated a great potential of the impedance-based system for noninvasive and real-time monitoring of cellular fate.

Granulocytic maturation in cultures of acute myeloid leukemia is not always accompanied by increased apoptosis

In this issue of the Journal, Soucek et al. challenge the assumption that increased functional granulocytic maturation of HL-60, an ATRA-responsive acute myeloid leukemia cell line devoid of the APL-specific PML-RARalpha fusion protein, results in more rapid or more sustained cell death. In this model cell line, the authors demonstrate that TGFbeta1, a well-known haemopoietic growth factor, enhances retinoid-dependent cyto-differentiation and growth arrest while inhibiting apoptosis. Concomitantly, treatment of HL-60 cells with the combination of TGFbeta1 and the retinoid partially suppresses ATRA-dependent induction of TRAIL. This is a death receptor ligand of the TNF family implicated in the paracrine mechanism underlying the apoptotic action of ATRA in APL blasts The protein activates the death-receptor-dependent or extrinsic apoptotic pathway, which is associated with caspase-8 activation. Down-regulation of TRAIL is correlated to an increase in the levels of the anti-apoptotic c-FLIP(L) and Mcl-1 proteins that are likely to be involved in the suppression of caspase-8 activation and apoptosis.