Ral (Ras like) leads an important proto-oncogenic signaling pathway down-stream of Ras. In this work, RalA was found to be significantly overactivated in hepatocellular carcinoma (HCC) cells and tissues as compared to non-malignant samples. Other elements of RalA pathway such as RalBP1 and RalGDS were also expressed at higher levels in malignant samples. Inhibition of RalA by gene-specific silencing caused a robust decrease in the viability and invasiveness of HCC cells. Additionally, the use of geranyl-geranyl transferase inhibitor (GGTI, an inhibitor of Ral activation) and Aurora kinase inhibitor II resulted in a significant decrease in the proliferation of HCC cells. Furthermore, RalA activation was found to be at a higher level of activation in HCC stem cells that express CD133. Transgenic mouse model for HCC (FXR-Knockout) also revealed an elevated level of RalA-GTP in the liver tumors as compared to background animals. Finally, subcutaneous mouse model for HCC confirmed effectiveness of inhibition of aurora kinase/RalA pathway in reducing the tumorigenesis of HCC cells in vivo. In conclusion, RalA overactivation is an important determinant of malignant phenotype in differentiated and stem cells of HCC and can be considered as a target for therapeutic intervention.

The Ral (Ras‐Like) signaling pathway plays an important role in the biology of cells. A plethora of effects is regulated by this signaling pathway and its prooncogenic effectors. Our team has demonstrated the overactivation of the RalA signaling pathway in a number of human malignancies including cancers of the liver, ovary, lung, brain, and malignant peripheral nerve sheath tumors. Additionally, we have shown that the activation of RalA in cancer stem cells is higher in comparison with differentiated cancer cells. In this article, we review the role of Ral signaling in health and disease with a focus on the role of this multifunctional protein in the generation of therapies for cancer. An improved understanding of this pathway can lead to development of a novel class of anticancer therapies that functions on the basis of intervention with RalA or its downstream effectors.

Current medication for gastric cancer patients has a low success rate with resistance and side effects. According to recent studies, γ-secretase inhibitors is used as therapeutic drugs in cancer. Moreover, all-trans retinoic acid (ATRA) is a natural compound proposed for the treatment/chemo-prevention of cancers. The aim of this study was to explore the effects of ATRA in combination with N-[N-(3,5-difluorophenacetyl-l-alanyl)]-S-phenylglycine t-butyl ester (DAPT) as γ-secretase inhibitor on viability and apoptosis of the AGS and MKN-45 derived from human gastric cancer. AGS and MKN-45 gastric cancer cell lines were treated with different concentrations of ATRA or DAPT alone or ATRA plus DAPT. The viability, death detection and apoptosis of cells was examined by MTT assay and Ethidium bromide/acridine orange staining. The distribution of cells in different phases of cell cycle was also evaluated through flow cytometry analyses. In addition, caspase 3/7 activity and the expression of caspase-3 and bcl-2 were examined. DAPT and ATRA alone decreased gastric cancer cells viability in a concentration dependent manner. The combination of DAPT and ATRA exhibited significant synergistic inhibitory effects. The greater percentage of cells were accumulated in G0/G1 phase of cell cycle in combination treatment. The combination of DAPT and ATRA effectively increased the proportion of apoptotic cells and the level of caspase 3/7 activities compared to single treatment. Moreover, augmented caspase-3 up-regulation and bcl-2 down-regulation were found following combined application of DAPT and ATRA. The combination of DAPT and ATRA led to more reduction in viability and apoptosis in respect to DAPT or ATRA alone in the investigated cell lines.

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The main aim of this study was to evaluate the expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and inducible nitric oxide synthase (iNOS) as host factors, and proviral load as the viral parameter, in adult T-cell leukemia/lymphoma (ATLL) individuals and healthy carrier (HC(s)) groups. Peripheral blood mononuclear cells (PBMC) from ATLL patients (n = 17) and HC subjects (as the control group, n = 17) were evaluated using real-time PCR to determine the levels of HTLV-1 proviral load and mRNA expression of ICAM, VCAM-1, and iNOS. ICAM-1 was significantly lower in ATLL patients than in control subjects. Although the expression of VCAM-1 was higher in ATLL individuals, there was no significant difference between the studied groups. In addition, no iNOS expression was found in ATLL patients, when compared to the HCs subjects, while ATLL patients demonstrated a higher level of proviral load when compared to the control group. Considering the importance of ICAM-1 in facilitating immune recognition of infected cells, it is posited that reduction of ICAM-1 expression is a unique strategy for circumventing appropriate immune responses that are mediated by different accessory proteins. Additionally, as the viral regulatory protein Tax and the NF-κB pathway play pivotal roles in expression of iNOS, lack of the latter in ATLL patients may be related to the level of Tax expression, disruption of the NF-κB pathway, or the occurrence of epigenetical mechanisms in the human iNOS promoter. Further studies are recommended to gain a better understanding of the interaction between host and viral factors in HTLV-1 pathogenesis and to identify a possible therapeutic target for ATLL.