Retinoic acid and cAMP inhibit rat hepatocellular carcinoma cell proliferation and enhance cell differentiation

Involvement of calmodulin-dependent protein kinase I in the regulation of the expression of connexin 43 in MA-10 tumor Leydig cells

Connexin 43 (Cx43, also known as Gja1) is the most abundant testicular gap junction protein. It has a crucial role in the support of spermatogenesis by Sertoli cells in the seminiferous tubules as well as in androgen synthesis by Leydig cells. The multifunctional family of Ca²⁺/calmodulin-dependent protein kinases (CaMK) is composed of CaMK I, II, and IV and each can serve as a mediator of nuclear Ca²⁺ signals. These kinases can control gene expression by phosphorylation of key regulatory sites on transcription factors. Among these, AP-1 members cFos and cJun are interesting candidates that seem to cooperate with CaMKs to regulate Cx43 expression in Leydig cells. In this study, the Cx43 promoter region important for CaMK-dependent activation is characterized using co-transfection of plasmid reporter-constructs with different plasmids coding for CaMKs and/or AP-1 members in MA-10 Leydig cells. Here we report that the activation of Cx43 expression by cFos and cJun is increased by CaMKI. Furthermore, results from chromatin immunoprecipitation suggest that the recruitment of AP-1 family members to the proximal region of the Cx43 promoter may involve another uncharacterized AP-1 DNA regulatory element and/or protein-protein interactions with other partners. Thus, our data provide new insights into the molecular regulatory mechanisms that control mouse Cx43 transcription in testicular Leydig cells.

Evaluation of a DNA demethylating agent in combination with all-trans retinoic acid for IDH1-mutant gliomas

BACKGROUND

Isocitrate Dehydrogenase 1/2 (IDH1/2) mutations are diagnostic for Astrocytoma or Oligodendroglioma, IDH-mutant. In these IDH-mutant gliomas, retinoic acid-related gene expression is commonly silenced by DNA hypermethylation. DNA demethylating agents can epigenetically reprogram IDH-mutant cells and reduce proliferation, likely by re-expression of silenced tumor suppressor pathways. We hypothesized that DNA demethylation might restore the retinoic acid pathway and slow tumor growth. This was the rationale for a preclinical evaluation combining the DNA demethylating agent, 5-Azacytidine (5-Aza), and retinoic acid pathway activation with all-trans retinoic acid (atRA) in IDH-mutant glioma.

METHODS

In this study, we evaluated the effect of 5-Aza and atRA combination on cell proliferation, apoptosis and gene expression in human glioma cells. In addition, the efficacy of combination was tested in patient-derived xenograft (PDX) bearing the IDH1R132H mutation, utilizing subcutaneous and orthotopic models.

RESULTS

5-Aza reduced the DNA methylation profile and increased the gene expression of retinoic acid-related genes. Combination of 5-Aza and atRA reduced cell growth, increased differentiation marker expression, and apoptosis in IDH1R132H glioma cells. Mechanistically, 5-Aza sensitized IDHIR132H glioma cells to atRA via upregulation of the retinoic acid pathway. Importantly, the drug combination reduced significantly the growth rate of subcutaneous tumors, but in an orthotopic mouse model the combination did not improve survival and 5-Aza alone provided the best survival benefit.

CONCLUSION

Use of DNA demethylating agent in combination with retinoids shows promise, but further optimization and preclinical studies are required for treatment of intracranial IDH-mutant gliomas.

Connexins and cAMP Cross-Talk in Cancer Progression and Metastasis

Simple Summary

Different connexins play diverse roles in cancers, either tumor-suppressing or tumor-promoting. In lung cancer, Cx43 serves as a tumor suppressor at the early stage, but it can also be a tumor-promotor at an advanced stage and during metastasis. Moreover, other connexins, including Cx26, Cx31.1, and Cx32, can be tumor suppressors. In contrast, Cx30.3 can be a tumor-promotor. The roles of different connexins in different cancers have also been established. Cx43 acts as a tumor suppressor in colorectal cancer, breast cancer, and glioma, whereas Cx32 can be a suppressor in liver tumors and hepatocarcinogenesis. Cx26 can be a tumor suppressor in mammary tumors; in contrast, it can be a tumor-promotor in melanoma. Existing drugs/molecules targeting the cAMP/PKA/connexin axis act to regulate channel opening/closing. Mimic peptides, such as Gap19, Gap26, and Gap 27 block hemichannels, mimetic peptides, and CT9/CT10 and promote hemichannel opening and also hemichannel closing.

Abstract

Connexin-containing gap junctions mediate the direct exchange of small molecules between cells, thus promoting cell–cell communication. Connexins (Cxs) have been widely studied as key tumor-suppressors. However, certain Cx subtypes, such as Cx43 and Cx26, are overexpressed in metastatic tumor lesions. Cyclic adenosine monophosphate (cAMP) signaling regulates Cx expression and function via transcriptional control and phosphorylation. cAMP also passes through gap junction channels between adjacent cells, regulating cell cycle progression, particularly in cancer cell populations. Low levels of cAMP are sufficient to activate key effectors. The present review evaluates the mechanisms underlying Cx regulation by cAMP signaling and the role of gap junctions in cancer progression and metastasis. A deeper understanding of these processes might facilitate the development of novel anticancer drugs.

Regulation of Female Folliculogenesis by Tsp1a in Nile Tilapia (Oreochromis niloticus)

TSP1 was reported to be involved in multiple biological processes including the activation of TGF-β signaling pathways and the regulation of angiogenesis during wound repair and tumor growth, while its role in ovarian folliculogenesis remains to be elucidated. In the present study, Tsp1a was found to be expressed in the oogonia and granulosa cells of phase I to phase IV follicles in the ovaries of Nile tilapia by immunofluorescence. tsp1a homozygous mutants were generated by CRISPR/Cas9. Mutation of tsp1a resulted in increased oogonia, reduced secondary growth follicles and delayed ovary development. Expression of the cell proliferation marker PCNA was significantly up-regulated in the oogonia of the mutant ovaries. Furthermore, transcriptomic analysis revealed that expressions of DNA replication related genes were significantly up-regulated, while cAMP and MAPK signaling pathway genes which inhibit cell proliferation and promote cell differentiation were significantly down-regulated. In addition, aromatase (Cyp19a1a) expression and serum 17β-estradiol (E2) concentration were significantly decreased in the mutants. These results indicated that lacking tsp1a resulted in increased proliferation and inhibited differentiation of oogonia, which in turn, resulted in increased oogonia, reduced secondary growth follicles and decreased E2. Taken together, our results indicated that tsp1a was essential for ovarian folliculogenesis in Nile tilapia.

Targeting Cyclic AMP Signalling in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a major healthcare problem worldwide, representing one of the leading causes of cancer mortality. Since there are currently no predictive biomarkers for early stage diagnosis, HCC is detected only in advanced stages and most patients die within one year, as radical tumour resection is generally performed late during the disease. The development of alternative therapeutic approaches to HCC remains one of the most challenging areas of cancer. This review focuses on the relevance of cAMP signalling in the development of hepatocellular carcinoma and identifies the modulation of this second messenger as a new strategy for the control of tumour growth. In addition, because the cAMP pathway is controlled by phosphodiesterases (PDEs), targeting these enzymes using PDE inhibitors is becoming an attractive and promising tool for the control of HCC. Among them, based on current preclinical and clinical findings, PDE4-specific inhibitors remarkably demonstrate therapeutic potential in the management of cancer outcomes, especially as adjuvants to standard therapies. However, more preclinical studies are warranted to ascertain their efficacy during the different stages of hepatocyte transformation and in the treatment of established HCC.

Analysis of competing endogenous RNA network identifies a poorly differentiated cancer-specific RNA signature for hepatocellular carcinoma

Plenty of evidence has suggested that long noncoding RNAs (lncRNAs) play a vital role in competing endogenous RNA (ceRNA) networks. Poorly differentiated hepatocellular carcinoma (PDHCC) is a malignant phenotype. This paper aimed to explore the effect and the underlying regulatory mechanism of lncRNAs on PDHCC as a kind of ceRNA. Additionally, prognosis prediction was assessed. A total of 943 messenger RNAs (mRNAs), 86 miRNAs, and 468 lncRNAs that were differentially expressed between 137 PDHCCs and 235 well-differentiated HCCs were identified. Thereafter, a ceRNA network related to the dysregulated lncRNAs was established according to bioinformatic analysis and included 29 lncRNAs, 9 miRNAs, and 96 mRNAs. RNA-related overall survival (OS) curves were determined using the Kaplan-Meier method. The lncRNA ARHGEF7-AS2 was markedly correlated with OS in HCC (P = .041). Moreover, Cox regression analysis revealed that patients with low ARHGEF7-AS2 expression were associated with notably shorter survival time (P = .038). In addition, the area under the curve values of the lncRNA signature for 1-, 3-, and 5-year survival were 0.806, 0.741, and 0.701, respectively. Furthermore, a lncRNA nomogram was established, and the C-index of the internal validation was 0.717. In vitro experiments were performed to demonstrate that silencing ARHGEF7-AS2 expression significantly promoted HCC cell proliferation and migration. Taken together, our findings shed more light on the ceRNA network related to lncRNAs in PDHCC, and ARHGEF7-AS2 may be used as an independent biomarker to predict the prognosis of HCC.

Retinol palmitate and ascorbic acid: Role in oncological prevention and therapy

Cancer development has been directly related to oxidative stress. During chemotherapy, some cancer patients use dietary antioxidants to avoid nutritional deficiencies due to cancer treatment. Among the antioxidants consumed, there are vitamins, including retinyl palmitate (PR) and ascorbic acid (AA), which have the capacity to reduce free radicals formation, protect cellular structures and maintain the cellular homeostasis. This systematic review evaluated the antioxidant and antitumor mechanisms of retinol palmitate (a derivative of vitamin A) and/or ascorbic acid (vitamin C) in cancer-related studies. Ninety-seven (97) indexed articles in the databases PubMed and Science Direct, published between 2013 and 2017, including 23 clinical studies (5 for every single compound while 13 in interaction) and 74 non-clinical studies (37 for retinol palmitate, 36 for ascorbic acid and 1 in interaction) were considered. Antioxidant and antitumor effects, with controversies over dosage and route of administration, were observed for the test compounds in their isolated form or associated in clinical studies. Prevention of cancer risks against oxidative damage was seen in lower doses of retinol palmitate and/or vitamin C. However, at high doses, they can generate reactive oxygen species, cytotoxicity and apoptosis in test systems. Non-clinical studies using cell lines have allowed understanding the mechanisms related to antioxidants and antitumor effects of the isolated compounds, however, studies on vitamin interactions, acting as antioxidants and/or antitumor are still rare and controversial. More studies, mainly related to modulation of antineoplastic drugs are needed for understanding the risks and benefits of their use during treatment in order to achieve effectiveness in cancer therapy and patient's quality of life.

Diprophylline inhibits non-small cell lung cancer A549 cell proliferation and migration, and promotes apoptosis, by downregulating PI3K signaling pathway

Diprophylline (DPL) is identified as a methylxanthine (MX) derivative. A number of MX derivatives are reported to have anti-tumor effects. However, it is not clear whether DPL has a therapeutic effect on non-small cell lung cancer (NSCLC). The aim of the present study was to investigate the effects of DPL on NSCLC and to elucidate the potential underlying mechanism. A Cell Counting Kit-8 assay was used to evaluate the potential effect of DPL on A549 cell proliferation. Transwell invasion and migration assays were performed to assess the effect of DPL on A549 cell migration and invasion. Furthermore, the percentage of apoptotic cells was detected by flow cytometric analysis, and proteins associated with apoptosis, including apoptosis regulator Bcl-2, apoptosis regulator BAX and active caspase-3, were examined by western blotting. Finally, the expression levels of molecules relevant to phosphoinositide 3-kinase (PI3K) signaling were detected by western blot analysis. The present study demonstrated that DPL may significantly inhibit A549 cell proliferation, migration and invasion. Furthermore, treatment with DPL may significantly induce A549 cell apoptosis. Finally, the protein expression levels associated with the PI3K signaling pathway were significantly inhibited in A549 cells following treatment with DPL. In conclusion, DPL may inhibit the proliferation and migration of NSCLC by inactivating the PI3K signaling pathway, and DPL is a promising novel therapeutic drug for NSCLC.

Control of nongenetic heterogeneity in growth rate and stress tolerance of Saccharomyces cerevisiae by cyclic AMP-regulated transcription factors

Genetically identical cells exhibit extensive phenotypic variation even under constant and benign conditions. This so-called nongenetic heterogeneity has important clinical implications: within tumors and microbial infections, cells show nongenetic heterogeneity in growth rate and in susceptibility to drugs or stress. The budding yeast, Saccharomyces cerevisiae, shows a similar form of nongenetic heterogeneity in which growth rate correlates positively with susceptibility to acute heat stress at the single-cell level. Using genetic and chemical perturbations, combined with high-throughput single-cell assays of yeast growth and gene expression, we show here that heterogeneity in intracellular cyclic AMP (cAMP) levels acting through the conserved Ras/cAMP/protein kinase A (PKA) pathway and its target transcription factors, Msn2 and Msn4, underlies this nongenetic heterogeneity. Lower levels of cAMP correspond to slower growth, as shown by direct comparison of cAMP concentration in subpopulations enriched for slower vs. faster growing cells. Concordantly, an endogenous reporter of this pathway’s activity correlates with growth in individual cells. The paralogs Msn2 and Msn4 differ in their roles in nongenetic heterogeneity in a way that demonstrates slow growth and stress tolerance are not inevitably linked. Heterogeneity in growth rate requires each, whereas only Msn2 is required for heterogeneity in expression of Tsl1, a subunit of trehalose synthase that contributes to acute-stress tolerance. Perturbing nongenetic heterogeneity by mutating genes in this pathway, or by culturing wild-type cells with the cell-permeable cAMP analog 8-bromo-cAMP or the PKA inhibitor H89, significantly impacts survival of acute heat stress. Perturbations that increase intracellular cAMP levels reduce the slower-growing subpopulation and increase susceptibility to acute heat stress, whereas PKA inhibition slows growth and decreases susceptibility to acute heat stress. Loss of Msn2 reduces, but does not completely eliminate, the correlation in individual cells between growth rate and acute-stress survival, suggesting a major role for the Msn2 pathway in nongenetic heterogeneity but also a residual benefit of slow growth. Our results shed light on the genetic control of nongenetic heterogeneity and suggest a possible means of defeating bet-hedging pathogens or tumor cells by making them more uniformly susceptible to treatment.

Nongenetic heterogeneity exists when a trait differs among individuals that have identical genotypes and environments. A clonal population can maximize its long-term success in an uncertain environment by diversifying its phenotypes via nongenetic heterogeneity: the currently unfavored ones may become the favored ones when conditions change. Nongenetic heterogeneity has clinical relevance. For example, populations of tumor cells or infectious microbes show cell-to-cell differences in growth and in drug or stress tolerance. This heterogeneity hampers efficient treatment and can potentiate harmful evolution of a tumor or pathogen. We show that in budding yeast, heterogeneity in intracellular cyclic AMP levels acting through the conserved Ras/cAMP/protein kinase A (PKA) pathway and its target transcription factors, Msn2 and Msn4, underlies the nongenetic heterogeneity of both single-cell growth rate and acute heat-stress tolerance. Perturbations of this pathway significantly affect population survival upon acute heat stress. These results illuminate a mechanism of nongenetic heterogeneity and suggest the potential value of antitumor or antifungal treatment strategies that target nongenetic heterogeneity to render the tumor or pathogen population more uniformly susceptible to a second drug that aims to kill.

Connexins, E-cadherin, Claudin-7 and β-catenin transiently form junctional nexuses during the post-natal mammary gland development

Gap junctions are intercellular channels made of connexins (Cxs) that allow direct communication between adjacent cells. Modulation of Cxs has been associated with abnormal development and function of the mammary gland and breast cancer. However, the mechanisms underlying their expression during normal mammary gland are not yet known. Cxs interact with components of tight and adherens junctions. Thus, we hypothesized that the expression levels of Cxs vary during mammary gland development and are regulated through stage-dependent interactions with members of the tight and adherens junctions. Our specific objectives were to: 1) determine the expression of Cxs and tight and adherens junction proteins throughout development and 2) characterize Cxs interactions with components of tight and adherens junctions. Murine mammary glands were sampled at various developmental stages (pre-pubescent to post-weaning). RT-qPCR and western-blot analyses demonstrated differential expression patterns for all gap (Cx43, Cx32, Cx26, Cx30), tight (Claudin-1, -3, -4, -7) and adherens (β-catenin, E- and P-cadherins) junctions throughout development. Interestingly, co-immunoprecipitation demonstrated interactions between these different types of junctions. Cx30 interacted with Cx26 just at the late pregnancy stage. While Cx43 showed a persistent interaction with β-catenin from virginity to post-weaning, its interactions with E-cadherin and Claudin-7 were transient. Cx32 interacted with Cx26, E-cadherin and β-catenin during lactation. Immunofluorescence results confirmed the existence of a junctional nexus that remodeled during mammary gland development. Together, our results confirm that the expression levels of Cxs vary concomitantly and that Cxs form junctional nexuses with tight and adherens junctions, suggesting the existence of common regulatory pathways.

7-Epiclusianone, a Benzophenone Extracted from Garcinia brasiliensis (Clusiaceae), Induces Cell Cycle Arrest in G1/S Transition in A549 Cells

Lung cancer is the leading cause of cancer deaths in the world. Disease stage is the most relevant factor influencing mortality. Unfortunately, most patients are still diagnosed at an advanced stage and their five-year survival rate is only 4%. Thus, it is relevant to identify novel drugs that can improve the treatment options for lung cancer. Natural products have been an important source for the discovery of new compounds with pharmacological potential including antineoplastic agents. We have previously isolated a prenylated benzophenone (7-epiclusianone) from Garcinia brasiliensis (Clusiaceae) that has several biological properties including antiproliferative activity against cancer cell lines. In continuation with our studies, the present work aimed to investigate the mechanisms involved with antiproliferative activity of 7-epiclusianone in A549 cells. Our data showed that 7-epiclusianone reduced the viability of A549 cells in a concentration-dependent manner (IC50 of 16.13 ± 1.12 μM). Cells were arrested in G1/S transition and apoptosis was induced. In addition, we observed morphological changes with cytoskeleton disorganization in consequence of the treatment. Taken together, the results showed that cell cycle arrest in G1/S transition is the main mechanism involved with antiproliferative activity of 7-epiclusianone. Our results are promising and open up the prospect of using this compound in further anticancer in vivo studies.

The multiple facets of drug resistance: one history, different approaches

Some cancers like melanoma and pancreatic and ovarian cancers, for example, commonly display resistance to chemotherapy, and this is the major obstacle to a better prognosis of patients. Frequently, literature presents studies in monolayer cell cultures, 3D cell cultures or in vivo studies, but rarely the same work compares results of drug resistance in different models. Several of these works are presented in this review and show that usually cells in 3D culture are more resistant to drugs than monolayer cultured cells due to different mechanisms. Searching for new strategies to sensitize different tumors to chemotherapy, many methods have been studied to understand the mechanisms whereby cancer cells acquire drug resistance. These methods have been strongly advanced along the years and therapies using different drugs have been increasingly proposed to induce cell death in resistant cells of different cancers. Recently, cancer stem cells (CSCs) have been extensively studied because they would be the only cells capable of sustaining tumorigenesis. It is believed that the resistance of CSCs to currently used chemotherapeutics is a major contributing factor in cancer recurrence and later metastasis development. This review aims to appraise the experimental progress in the study of acquired drug resistance of cancer cells in different models as well as to understand the role of CSCs as the major contributing factor in cancer recurrence and metastasis development, describing how CSCs can be identified and isolated.

Role of heteromeric gap junctions in the cytotoxicity of cisplatin

In several systems, the presence of gap junctions made of a single connexin has been shown to enhance the cytotoxicity of cisplatin. However, most gap junction channels in vivo appear to be heteromeric (composed of more than one connexin isoform). Here we explore in HeLa cells the cytotoxicity to cisplatin that is enhanced by heteromeric gap junctions composed of Cx26 and Cx32, which have been shown to be more selective among biological permeants than the corresponding homomeric channels. We found that survival and subsequent proliferation of cells exposed to cisplatin were substantially reduced when gap junctions were present than when there were no gap junctions. Functional inhibition of gap junctions by oleamide enhanced survival/proliferation, and enhancement of gap junctions by retinoic acid decreased survival/proliferation. These effects occurred only in high density cultures, and the treatments were without effect when there was no opportunity for gap junction formation. The presence of functional gap junctions enhanced apoptosis as reflected in markers of both early-stage and late-stage apoptosis. Furthermore, analysis of caspases 3, 8 and 9 showed that functional gap junctions specifically induced apoptosis by the mitochondrial pathway. These results demonstrate that heteromeric Cx26/Cx32 gap junctions increase the cytotoxicity of cisplatin by induction of apoptosis via the mitochondrial pathway.

All-trans retinoic acid protects hepatocellular carcinoma cells against serum-starvation-induced cell death by upregulating collagen 8A2

As a therapeutic or chemopreventative agent for various cancers, all-trans retinoic acid (atRA) has been reported to inhibit growth, induce apoptosis or cause differentiation. It was found that atRA could protect hepatocellular carcinoma (HCC) cells against cell death induced by serum starvation. Furthermore, it was found that atRA could enhance cell adhesion, but had no effect on the cell cycle and apoptosis. Using an Illumina Human HT-12 v4 expression microarray, 207 upregulated and 173 downregulated genes were identified in HepG2 cells treated with atRA. The most upregulated genes are cytochrome P450 family 26 subfamily A polypeptide 1 (CYP26A1), histidine triad nucleotide binding protein 3 (HINT3), miR-1282 and cytochrome P450 family 26 subfamily B polypeptide 1 (CYP26B1), which showed more than fivefold greater expression. Using Gene Ontology analysis, the greatest significance was found in extracellular-matrix-related molecular functions and the cellular component in upregulated genes. The upregulation of collagen 8A2 (COL8A2) was further confirmed using quantitative RT-PCR and western blotting. Knockdown of COL8A2 blocked enhancement in the early stage of cell adhesion by atRA treatment. Re-expression of COL8A2 in COL8A2-knocked-down HCC cells reversed the effect of small interfering RNA-COL8A2. In addition, COL8A2 could increase HCC cell migration and invasion. Thus, COL8A2 was identified as the key protein involved in the enhancement of cell adhesion of atRA under serum-free conditions. In conclusion, atRA protects HCC cells against serum-starvation-induced cell death by enhancing cell adhesion, and COL8A2 plays an important role in HCC cell migration and invasion.

Treatment with baicalin up-regulates the expression of connexion 26 and connexion 43 in human hepatocellular carcinoma cell line SMMC-7721

AIM: To investigate the effect of treatment with baicalin on the expression of connexion 26 (Cx26) and connexion 43 (Cx43) in human hepatocellular cell line SMMC-7721.

METHODS: SMMC-7721 cells were randomly divided into 4 groups: normal control group, low-dose (10 mg/L) baicalin group, medium-dose (20 mg/L) baicalin group, and high-dose (40 mg/L) baicalin group. Gap junction intercellular communication (GJIC) was measured by scrap loading/dye transfer assay (SL/DT). The expression of Cx26 and Cx43 mRNAs in SMMC-7721 cells was determined by RT-PCR. The expression of Cx26 protein was detected by Western blot, and that of Cx43 protein was detected by immunohistochemistry.

RESULTS: Compared to the normal control group, the expression of Cx26 mRNA and protein was significantly enhanced in SMMC-7721 cells treated with low, medium and high concentrations of baicalin (mRNA: 0.148 ± 0.111, 10.253 ± 0.222, 17.283 ± 0.024 vs 0.138 ± 0.111; all P < 0.05; protein: 0.516 ± 0.029, 0.759 ± 0.020, 1.019 ± 0.076 vs 0.367 ± 0.029; all P < 0.05). Compared to the normal control group, the expression of Cx43 mRNA showed no significant changes, but the expression of Cx43 protein was significantly enhanced in SMMC-7721 cells treated with different concentrations of baicalin.

CONCLUSION: Restoration or enhancement of GJIC induced by up-regulation of Cx26 and Cx43 is likely to be an important molecular mechanism by which baicalin inhibits tumor growth.