Advanced progress on the relationship between RA and its receptors and malignant tumors

Current Opportunities for Targeting Dysregulated Neurodevelopmental Signaling Pathways in Glioblastoma

Glioblastoma (GBM) is the most common and highly lethal type of brain tumor, with poor survival despite advances in understanding its complexity. After current standard therapeutic treatment, including tumor resection, radiotherapy and concomitant chemotherapy with temozolomide, the median overall survival of patients with this type of tumor is less than 15 months. Thus, there is an urgent need for new insights into GBM molecular characteristics and progress in targeted therapy in order to improve clinical outcomes. The literature data revealed that a number of different signaling pathways are dysregulated in GBM. In this review, we intended to summarize and discuss current literature data and therapeutic modalities focused on targeting dysregulated signaling pathways in GBM. A better understanding of opportunities for targeting signaling pathways that influences malignant behavior of GBM cells might open the way for the development of novel GBM-targeted therapies.

Calcitriol Suppresses Warburg Effect and Cell Growth in Human Colorectal Cancer Cells

Increasing lines of evidence indicate that the biologically active form of vitamin D, calcitriol (1,25-dihydroxyvitamin D₃), prevents cancer progression by reducing cell proliferation, increasing cell differentiation, and inhibiting angiogenesis, among other potential roles. Cancer cells in solid tumors preferably undergo the “Warburg effect” to support cell growth by upregulating glycolysis, and the glycolytic intermediates further serve as building blocks to generate biomass. The objective of the current study is to investigate whether calcitriol affects glucose metabolism and cell growth in human colorectal cancer cells. Calcitriol reduced the expression of cyclin D1 and c-Myc. In addition, calcitriol reduced the expression of glucose transporter 1 (GLUT1) and key glycolytic enzymes and decreased extracellular acidification rate but increased oxygen consumption rate in human colorectal cancer cells. In a subcutaneous HT29 xenograft NOD/SCID mouse model, the volume and weight of the tumors were smaller in the calcitriol groups as compared with the control group, and the expression levels of GLUT1 and glycolytic enzymes, hexokinase 2 and lactate dehydrogenase A, were also lower in the calcitriol groups in a dose-responsive manner. Our data indicate that calcitriol suppresses glycolysis and cell growth in human colorectal cancer cells, suggesting an inhibitory role of the biologically active form of vitamin D in colorectal cancer progression.

Bottom up proteomics identifies neuronal differentiation pathway networks activated by cathepsin inhibition treatment in neuroblastoma cells that are enhanced by concurrent 13-cis retinoic acid treatment

Neuroblastoma is the second most common pediatric cancer involving the peripheral nervous system in which stage IVS metastatic tumors regress due to spontaneous differentiation. 13-cis retinoic acid (13-cis RA) is currently used in the clinic for its differentiation effects and although it improves outcomes, relapse is seen in half of high-risk patients. Combinatorial therapies have been shown to be more effective in oncotherapy and since cathepsin inhibition reduces tumor growth, we explored the potential of coupling 13-cis RA with a cathepsin inhibitor (K777) to enhance therapeutic efficacy against neuroblastoma. Shotgun proteomics was used to identify proteins affected by K777 and dual (13-cis RA/K777) treatment in neuroblastoma SK-N-SH cells. Cathepsin inhibition was more effective in increasing proteins involved in neuronal differentiation and neurite outgrowth than 13-cis RA alone, but the combination of both treatments enhanced the neuronal differentiation effect. SIGNIFICANCE: As neuroblastoma can spontaneously differentiate, determining which proteins are involved in differentiation can guide development of more accurate diagnostic markers and more effective treatments. In this study, we established a differentiation proteomic map of SK-N-SH cells treated with a cathepsin inhibitor (K777) and K777/13-cis RA (dual). Bioinformatic analysis revealed these treatments enhanced neuronal differentiation and axonogenesis pathways. The most affected proteins in these pathways may become valuable biomarkers of efficacy of drugs designed to enhance differentiation of neuroblastoma [1].

All-trans retinoic acid reverses malignant biological behavior of hepatocarcinoma cells by regulating miR-200 family members

As a potential chemo-therapeutic agent, all-trans retinoic acid (ATRA) can significantly reverse epithelial-mesenchymal transition (EMT) of hepal-6 hepatocarcinoma cell line in vitro, but the mechanism is unclear. The expression profile of microRNA-200 (miR-200) families is different in hepatocellular carcinoma. In this study, we found that ATRA treatment could up-regulate the expression of miR-200a-3p, 200c-3p, and 141-3p, which were involved in ATRA regulated proliferation and apoptosis of hepal-6 cell, but not colony formation. Meanwhile, miR-200a-3p, 200c-3p, and 141-3p could recovery ATRA inhibited migration and invasion abilities of hepal-6 cells at various levels. miR-200a-3p and 200c-3p prevented ATRA from inducing the differentiation and hepatic functions of hepal-6 cells. Antagomir specific for miR-200a-3p and 200c-3p down-regulated the expression of CK18, but only miR-200a-3p antagomir played prominent role in regulating the expression of these mesenchymal markers, N-Cadherin, Snail and Twist. The transcriptional activities of 8 transcription factors were up-regulated and 35 transcription factors were down-regulated by ATRA. Compared with ATRA group, inhibition of miR-200a-3p, 200c-3p, and 141-3p significantly strengthened the expression of Fra1/Jun (AP1), Ets1/PEA3, Brn3, and Zeb1/AREB6 at varying degrees. Therefore, this result suggested that ATRA may suppress EMT through down-regulating miR-200a-3p, 200c-3p and 141-3p related transcription factors. miR-200 and their downstream genes might be the potentially specific targets for the treatment of hepatocarcinoma.

Bottom up proteomics reveals novel differentiation proteins in neuroblastoma cells treated with 13-cis retinoic acid

Neuroblastoma, a cancer of the sympathetic nervous system, is the second most common pediatric cancer. A unique feature of neuroblastoma is remission in some patients due to spontaneous differentiation of metastatic tumors. 13-cis retinoic acid (13-cis RA) is currently used in the clinic to treat neuroblastoma due to its differentiation inducing effects. In this study, we used shotgun proteomics to identify proteins affected by 13-cis RA treatment in neuroblastoma SK-N-SH cells. Our results showed that 13-cis RA reduced proteins involved in extracellular matrix synthesis and organization and increased proteins involved in cell adhesion and neurofilament formation. These changes indicate that 13-cis RA induces tumor cell differentiation by decreasing extracellular matrix rigidity and increasing neurite overgrowth. Differentially-affected proteins identified in this study may be novel biomarkers of drug efficacy in the treatment of neuroblastoma. SIGNIFICANCE: As neuroblastoma can spontaneously differentiate, determining which proteins are involved in differentiation can guide development of novel treatments. 13-cis retinoic acid is currently used in the clinic as a differentiation inducer. Here we have established a proteome map of SK-N-SH cells treated with 13-cis retinoic acid. Bioinformatic analysis revealed the involvement of development, differentiation, extracellular matrix assembly, collagen biosynthesis, and neurofilament bundle association. This proteome map provides information as to which proteins are important for differentiation and identifies networks that can be targeted by drugs to treat neuroblastoma [1].

Dual effects of the Nrf2 inhibitor for inhibition of hepatitis C virus and hepatic cancer cells

BACKGROUND

We previously showed that knockdown of nuclear factor E2-related factor 2 (Nrf2) resulted in suppression of hepatitis C virus (HCV) infection. In this study, whether brusatol, an Nrf2 inhibitor, has dual anti-HCV and anticancer effects was explored.

METHODS

The anti-HCV effect of brusatol was investigated by analyzing HCV RNA and proteins in a hepatic cell line persistently-infected with HCV, HPI cells, and by analyzing HCV replication in a replicon-replicating hepatic cell line, OR6 cells. Then, dual anti-HCV and anticancer effects of brusatol and enhancement of the effects by the combination of brusatol with anticancer drugs including sorafenib, which has been reported to have the dual effects, were then investigated.

RESULTS

Brusatol suppressed the persistent HCV infection at both the RNA and protein levels in association with a reduction in Nrf2 protein in the HPI cells. Analysis of the OR6 cells treated with brusatol indicated that brusatol inhibited HCV persistence by inhibiting HCV replication. Combination of brusatol with an anticancer drug not only enhanced the anticancer effect but also, in the case of the combination with sorafenib, strongly suppressed HCV infection.

CONCLUSIONS

Brusatol has dual anti-HCV and anticancer effects and can enhance the comparable effects of sorafenib. There is therefore the potential for combination therapy of brusatol and sorafenib for HCV-related hepatocellular carcinoma.

All-trans retinoic acid inhibits proliferation, migration, invasion and induces differentiation of hepa1-6 cells through reversing EMT in vitro

Hepatocellular carcinoma (HCC) has the characristics of tumor invasiveness, frequent intrahepatic spread and extra hepatic metastases, which affects the therapy efficiency and prognosis. Epithelial-mesenchymal transition (EMT) is now recognized as a key process in tumor invasion, metastasis and the generation of cancer initiating cells. All-trans retinoic acid (ATRA) is currently used as a potential chemo-therapeutic or chemo-preventive agent because of its anti-proliferative, pro-apoptotic and antioxidant properties. This study investigated the effects of ATRA at different concentrations on the proliferation, migration, invasion, differentiation and functions of the mouse hepa1-6 hepatocarcinoma cell line and explored whether ATRA regulates EMT in the antitumor process. Trypan blue staining and colony formation assay were used to detect cell proliferation. Wound-healing assay and Transwell Matrigel assay were performed to examine migration. Invasion was assessed by using Transwell invasion assay. In the present study, ATRA significantly inhibited the cell growth, colony formation, migration, and invasion capability of hepa1-6 cells in a dose-dependent manner. Furthermore, ATRA at low concentration (0.1 µmol/l) could generate these influences. After treated in the ATRA medium, the expression of mature hepatic markers ALB (albumin), CK18 (cytokeratin 18), TAT (tyrosine aminotransferase), ApoB (apolipoprotein B) decreased and that of hepatocarcinoma marker AFP (α fetoprotein) increased. At day 7 after ATRA induction, hepa1-6 cells showed comparable indocyanine green (ICG) uptake and glycogen storage function to the blank control. The mRNA expression of mesenchymal markers N-cadherin, vimentin, snail and twist decreased, while expression of epithelial marker E-cadherin increased in hepa1-6 cells after treated with ATRA. Therefore, this study demonstrates that ATRA remarkably suppressed the proliferation, migration, invasion of hepa1-6 hepatocarcinoma cell line and effectively induced its differentiation and liver functions in vitro through the reversal of EMT. HCC may be more sensitive to ATRA than other cancers, suggesting the prospective usefulness of ATRA in the treatment of HCC.

Additive Effects of Retinoic Acid (RA) and Bone Morphogenetic Protein 4 (BMP-4) Apoptosis Signaling in Retinoblastoma Cell Lines

Retinoids have been shown to serve promising therapeutic agents for human cancers, e.g. the treatment of neuroblastoma. Synthetic retinoids, specific for particular retinoic acid (RA) receptors, are tested as new therapy strategies. In the present study, application of recombinant retinoic acid (RA) lowers retinoblastoma (RB) cell viability and induces apoptosis in RB cell lines. Combined treatment of RA and bone morphogenetic protein 4 (BMP-4) increases the pro-apoptotic effect of RA in the RB cells lines WERI-Rb1, Y-79, RB355, RBL-30 and RBL-15, indicating an additive effect. We could show that in WERI-Rb1 cells RA/BMP-4 mediated cell death is at least partially caspase-dependent, whereby RA and BMP-4 additively increased (i) Apaf-1 mRNA levels, (ii) caspase-9 cleavage activity and (iii) the number of activated, cleaved caspase-3 positive cells. Compared to single application of RA and BMP-4, combined RA/BMP-4 treatment significantly augments mRNA levels of the retinoic acid receptors (RARs) RARα and RARß and the retinoic X receptor (RXR) RXRγ suggesting an interaction in the induction of these RA receptor subtypes in WERI-Rb1 cells. Agonist studies revealed that both, RARs and RXRs are involved in RA/BMP-4 mediated apoptosis in WERI-Rb1 retinoblastoma cells. Employing specific RAR subtype antagonists and a RXRß and RXRγ knockdown, we proved that RA/BMP-4 apoptosis signaling in WERI-Rb1 cells requires the RA receptor subtypes RARα, RARß, RXRß and RXRγ. Deciphering signaling mechanisms underlying apoptosis induction of RA and BMP-4 in WERI-Rb1 cells, our study provides useful starting-points for future retinoid-based therapy strategies in retinoblastoma.

Prostaglandin F2α regulates the expression of uterine activation proteins via multiple signalling pathways

Prostaglandin F2α (PGF2A) has multiple roles in the birth process in addition to its vital contractile role. Our previous study has demonstrated that PGF2A can modulate uterine activation proteins (UAPs) in cultured pregnant human myometrial smooth muscle cells (HMSMCs). The objective of this study was to define the signalling pathways responsible for PGF2A modulation of UAPs in myometrium. It was found that PGF2A stimulated the expression of (GJA1) connexin 43 (CX43), prostaglandin endoperoxide synthase 2 (PTGS2) and oxytocin receptor (OTR) in cultured HMSMCs. The inhibitors of phospholipase C (PLC) and protein kinase C (PKC) blocked PGF2A-stimulated expression of CX43. The inhibitors of ERK, P38 and NFκB also blocked the effect of PGF2A on CX43 expression, whereas PI3K and calcineurin/nuclear factor of activated T-cells (NFAT) pathway inhibitors did not reverse the effect of PGF2A on CX43. For PTGS2 and OTR, PLC, PI3K, P38 and calcineurin/NFAT signalling pathways were involved in PGF2A action, whereas PKC and NFκB signalling were not involved. In addition, PGF2A activated NFAT, PI3K, NFκB, ERK and P38 signalling pathways. Our data suggest that PGF2A stimulates CX43, PTGS2 and OTR through divergent signalling pathways.

Activation of RAS/ERK alone is insufficient to inhibit RXRα function and deplete retinoic acid in hepatocytes

Activation of RAS/ERK signaling pathway, depletion of retinoid, and phosphorylation of retinoid X receptor alpha (RXRα) are frequent events found in liver tumors and thought to play important roles in hepatic tumorigenesis. However, the relationships among them still remained to be elucidated. By exploring the transgenic mouse model of hepatic tumorigenesis induced by liver-specific expression of H-ras12V oncogene, the activation of RAS/ERK, the mRNA expression levels of retinoid metabolism-related genes, the contents of retinoid metabolites, and phosphorylation of RXRα were determined. RAS/ERK signaling pathway was gradually and significantly activated in hepatic tumor adjacent normal liver tissues (P) and hepatic tumor tissues (T) of H-ras12V transgenic mice compared with normal liver tissues (Wt) of wild type mice. On the contrary, the mRNA expression levels of retinoid metabolism-related genes were significantly reduced in P and T compared with Wt. Interestingly, the retinoid metabolites 9-cis-retinoic acid (9cRA) and all-trans-retinoic acid (atRA), the well known ligands for nuclear transcription factor RXR and retinoic acid receptor (RAR), were significantly decreased only in T compared with Wt and P, although the oxidized polar metabolite of atRA, 4-keto-all-trans-retinoic-acid (4-keto-RA) was significantly decreased in both P and T compared with Wt. To our surprise, the functions of RXRα were significantly blocked only in T compared with Wt and P. Namely, the total protein levels of RXRα were significantly reduced and the phosphorylation levels of RXRα were significantly increased only in T compared with Wt and P. Treatment of H-ras12V transgenic mice at 5-week-old or 5-month-old with atRA had no effect on the prevention of tumorigenesis or cure of developed nodules in liver. These events imply that the depletion of 9cRA and atRA and the inhibition of RXRα function in hepatic tumors involve more complex mechanisms besides the activation of RAS/ERK pathway.