BH3-only proteins in tumorigenesis and malignant melanoma

Super-enhancers: critical roles and therapeutic targets in hematologic malignancies

Super-enhancers (SEs) in a broad range of human cell types are large clusters of enhancers with aberrant high levels of transcription factor binding, which are central to drive expression of genes in controlling cell identity and stimulating oncogenic transcription. Cancer cells acquire super-enhancers at oncogene and cancerous phenotype relies on these abnormal transcription propelled by SEs. Furthermore, specific inhibitors targeting SEs assembly and activation have offered potential targets for treating various tumors including hematological malignancies. Here, we first review the identification, functional significance of SEs. Next, we summarize recent findings of SEs and SE-driven gene regulation in normal hematopoiesis and hematologic malignancies. The importance and various modes of SE-mediated MYC oncogene amplification are illustrated. Finally, we highlight the progress of SEs as selective therapeutic targets in basic research and clinical trials. Some open questions regarding functional significance and future directions of targeting SEs in the clinic will be discussed too.

microRNA-26a induces a mitochondrial apoptosis mediated by p53 through targeting to inhibit Mcl1 in human hepatocellular carcinoma

Aim

We have previously found that microRNA-26a (miR-26a) is a potential tumor suppressor in hepatocellular carcinoma (HCC). In this study, we further explored the roles of miR-26a in HCC apoptosis.

Methods

miR-26a expression levels were detected in HCC tissues by real-time PCR. Statistical analysis was performed to explore the correlation between miR-26a expression and apoptotic cells and the antiapoptotic protein levels. In vitro assays were performed to investigate the roles of miR-26a in HCC apoptosis. The immunohistochemical staining analysis, Western blot, and luciferase reporter assay were performed to evaluate the relationship between miR-26a and its potential upstream regulating and downstream target genes. The potential mechanism of the combination treatment of interferon-α1b (IFN-α1b) and 5-fluorouracil (5-FU) was explored by in vitro and in vivo assays.

Results

miR-26a levels were significantly associated with the number of apoptotic cells and inversely correlated with the protein levels of Bcl-2, Bcl-xL, and Mcl1 in HCC tissues. Furthermore, miR-26a was proved to induce the mitochondrial apoptosis in vitro by directly targeting to inhibit Mcl1 in HCC cells. Moreover, p53 was demonstrated to mediate miR-26a-induced apoptosis, by activating its promoter in HCC. Meanwhile, the combination treatment of IFN-α1b and 5-FU could induce the expression of p53, which then upregulated miR-26a and downregulated Mcl1 levels, and finally promoted the apoptosis of HCC cells through a mitochondrial pathway.

Conclusion

These findings highlight the important and related molecular mechanism of miR-26a in the regulation of apoptosis and implicate the potential application of combination of IFN-α1b and 5-FU in HCC treatment.

BH3-Only Proteins in Health and Disease

BH3-only proteins are proapoptotic members of the broader Bcl-2 family, which promote cell death by directly or indirectly activating Bax and Bak. The expression of BH3-only proteins is regulated both transcriptionally and posttranscriptionally in a cell type-specific and a tissue-specific manner. Research over the last 20 years has provided significant insights into their roles in tissue homeostasis and various pathologies, which in turn has led to the development of novel therapeutics for numerous diseases. In this review, a snapshot of the progress over this period is given, including our current understanding of their regulation, mode of action, role in mammalian development, and pathology.

Protective effects of camel milk against pathogenicity induced by Escherichia coli and Staphylococcus aureus in Wistar rats

The aim of the present study was to investigate the protective effects of camel milk on hepatic pathogenicity induced by experimental infection with Escherichia (E. coli) and Staphylococcus aureus (S. aureus) in Wistar rats. The rats were divided into six groups: The control and camel milk groups received water and camel milk, respectively; two groups received camel milk for 2 weeks prior to intraperitoneal injection of either E. coli or S. aureus; and two groups were injected intraperitoneally with E. coli and S. aureus, respectively. All animals were maintained under observation for 7 days prior to biochemical and gene expression analyses. The rats treated with camel milk alone exhibited no changes in expression levels of glutamic‑pyruvate transaminase (GPT) or glutamic‑oxaloacetic transaminase (GOT), compared with the water‑treated group. The E. coli‑ and S. aureus‑injected rats exhibited a significant increase in oxidative stress, and prior treatment with camel milk normalized the observed changes in the expression levels of GPT, GOT and malondialdehyde (MDA). Treatment with camel milk decreased the total bacterial count in liver tissue samples obtained from the rats injected with E. coli and S. aureus. Camel milk administration increased the expression levels of glutathione‑S‑transferase and superoxide dismutase, which were downregulated following E. coli and S. aureus injection. In addition, camel milk downregulated the increased expression of interleukin‑6 and apoptosis‑associated genes. Of note, administration of camel milk alone increased the expression levels of the B cell lymphoma 2‑associated X protein and survivin anti‑apoptotic genes, and supplementation prior to the injection of E. coli and S. aureus induced further upregulation, In conclusion, camel milk exerted protective effects against E. coli and S. aureus pathogenicity, by modulating the extent of lipid peroxidation, together with the antioxidant defense system, immune cytokines, apoptosis and the expression of anti-apoptotic genes in the liver of Wistar rats.

Role of Bcl-2 family proteins and caspases in the regulation of apoptosis

Apoptosis, or programmed cell death, plays a pivotal role in the elimination of unwanted, damaged, or infected cells in multicellular organisms and also in diverse biological processes, including development, cell differentiation, and proliferation. Apoptosis is a highly regulated form of cell death, and dysregulation of apoptosis results in pathological conditions including cancer, autoimmune and neurodegenerative diseases. The Bcl-2 family proteins are key regulators of apoptosis, which include both anti- and pro-apoptotic proteins, and a slight change in the dynamic balance of these proteins may result either in inhibition or promotion of cell death. Execution of apoptosis by various stimuli is initiated by activating either intrinsic or extrinsic pathways which lead to a series of downstream cascade of events, releasing of various apoptotic mediators from mitochondria and activation of caspases, important for the cell fate. In view of recent research advances about underlying mechanism of apoptosis, this review highlights the basics concept of apoptosis and its regulation by Bcl-2 family of protein. Furthermore, this review discusses the interplay of various apoptotic mediators and caspases to decide the fate of the cell. We expect that this review will add to the pool of basic information necessary to understand the mechanism of apoptosis which may implicate in designing better strategy to develop biomedical therapy to control apoptosis.

Apoptosis is associated with CD36/fatty acid translocase upregulation in non-alcoholic steatohepatitis

BACKGROUND & AIMS

Hepatocyte apoptosis is a key event in non-alcoholic steatohepatitis (NASH). We studied the effect of obesity on free fatty acid (FFA) levels, fatty acid transport proteins (FATPs) and on extrinsic and intrinsic activation of apoptosis in the liver.

METHODS

Liver biopsies were harvested from 52 morbidly obese patients [body mass index (BMI): 53.82+/-1.41; age: 45+/-10.50; 15 males/37 females] undergoing bariatric surgery, and were scored for NASH, evaluated for fibrosis, and investigated for intrahepatic expression of FATPs, death receptors and cytosolic apoptosis-related molecules. Findings were correlated with serum FFA levels and the degrees of intrahepatic (terminal dUTP nick end labelling) and systemic (M30) apoptosis.

RESULTS

In patients' liver sections, FATPs as well as select parameters of extrinsic and intrinsic apoptosis were found to be upregulated (CD36/FAT: x 11.56; FATP-5: x 1.33; CD95/Fas: x 3.18; NOXA: x 2.79). These findings correlated with significantly elevated serum FFAs (control: 14.72+/-2.32 mg/dl vs. patients: 23.03+/-1.24 mg/dl) and M30 levels (control: 83.12+/-7.46 U/L vs. patients: 212.61+/-22.16 U/L). We found correlations between FATPs and apoptosis mediators as well as with histological criteria of NASH and fibrosis.

CONCLUSIONS

Increased FFA and FATPs are associated with extrinsically and intrinsically induced apoptosis, liver damage and fibrosis in obese patients. Thus, FATPs may offer an interesting new approach to understand and potentially intervene NASH pathogenesis.

Resistance of cutaneous anaplastic large-cell lymphoma cells to apoptosis by death ligands is enhanced by CD30-mediated overexpression of c-FLIP

Death ligands, including TNF-alpha, CD95L/FasL, and TRAIL, mediate safeguard mechanisms against tumor growth and critically contribute to lymphocyte homeostasis. We investigated death receptor-mediated apoptosis and CD30/CD95 crosstalk in four CD30-positive cell lines of cutaneous anaplastic large-cell lymphoma (cALCL). Whereas CD95 stimulation strongly induced apoptosis in cALCL cells, the pro-apoptotic pathways of TNF-alpha and TRAIL were completely blocked at an early step. Expression of TNF receptor 1 was lost in three of four cell lines, providing an explanation for TNF-alpha unresponsiveness. TRAIL resistance may be explained by the consistent overexpression of cellular flice inhibitory protein (c-FLIP) (four of four cell lines) and frequent loss of the pro-apoptotic Bcl-2 protein Bid (three of four cell lines). Changes at the receptor-expression level were largely ruled out. CD30/CD95 crosstalk experiments showed that CD30 ligation leads to NF-kappaB-mediated c-FLIP upregulation in cALCL cells, which in turn conferred enhanced resistance to CD95-mediated apoptosis. Knockdown of c-FLIP by a lentiviral approach enhanced basic apoptosis rates in cALCL cells and diminished the CD30-mediated suppression of apoptosis, thus proving the significance of c-FLIP in this context. These in vitro findings may be indicative of the clinical situation of cALCL. Further clarifying the defects in apoptosis pathways in cutaneous lymphomas may lead to improved therapies for these disorders.

BH3-only proteins Mcl-1 and Bim as well as endonuclease G are targeted in spongistatin 1-induced apoptosis in breast cancer cells

Spongistatin 1, a marine experimental substance with chemotherapeutic potential, induces apoptosis and inhibits clonogenic survival of MCF-7 cells. Regarding the apoptotic signaling pathways of spongistatin 1, we present two major facts. Firstly, spongistatin 1-induced cell death, mainly caspase-independent, involves the proapoptotic proteins apoptosis-inducing factor and endonuclease G. Both proteins translocate from mitochondria to the nucleus and contribute to spongistatin 1-mediated apoptosis as shown via gene silencing. Secondly, spongistatin 1 acts as a tubulin depolymerizing agent and is able to free the proapoptotic Bcl-2 family member Bim from its sequestration both by the microtubular complex and by the antiapoptotic protein Mcl-1. Silencing of Bim by small interfering RNA leads to a diminished translocation of apoptosis-inducing factor and endonuclease G to the nucleus and subsequently reduces apoptosis rate. Thus, we identified Bim as an important factor upstream of mitochondria executing a central role in the caspase-independent apoptotic signaling pathway induced by spongistatin 1. Taken together, spongistatin 1 is both a valuable tool for the characterization of apoptotic pathways and a promising experimental anticancer drug.

BH3-only proteins in apoptosis and beyond: an overview

BH3-only BCL-2 family proteins are effectors of canonical mitochondrial apoptosis. They discharge their pro-apoptotic functions through BH1-3 pro-apoptotic proteins such as BAX and BAK, while their activity is suppressed by BH1-4 anti-apoptotic BCL-2 family members. The precise mechanism by which BH3-only proteins mediate apoptosis remains unresolved. The existing data are consistent with three mutually non-exclusive models (1) displacement of BH1-3 proteins from complexes with BH1-4 proteins; (2) direct interaction with and conformational activation of BH1-3 proteins; and (3) membrane insertion and membrane remodeling. The BH3-only proteins appear to play critical roles in restraining cancer and inflammatory diseases such as rheumatoid arthritis. Molecules that mimic the effect of BH3-only proteins are being used in treatments against these diseases. The cell death activity of a subclass of BH3-only members (BNIP3 and BNIP3L) is linked to cardiomyocyte loss during heart failure. In addition to their established role in apoptosis, several BH3-only members also regulate diverse cellular functions in cell-cycle regulation, DNA repair and metabolism. Several members are implicated in the induction of autophagy and autophagic cell death, possibly through unleashing of the BH3-only autophagic effector Beclin 1 from complexes with BCL-2/BCL-xL. The Chapters included in the current Oncogene Review issues provide in-depth discussions on various aspects of major BH3-only proteins.

Mitogen-activated protein kinase inhibition induces translocation of Bmf to promote apoptosis in melanoma

Constitutive activation of the mitogen-activated protein kinase (MAPK) pathway is implicated in the development and progression of many human cancers, including melanoma. Mutually exclusive activating mutations in NRAS or BRAF have been identified in approximately 85% of melanomas, and components of this pathway have been developed as molecular targets for therapeutic intervention. We and others have shown that inhibition of this pathway with specific small molecule MAPK/extracellular signal-regulated kinase kinase (MEK) inhibitors induces a wide range of apoptotic responsiveness in human melanoma cells both in vitro and in vivo. To define the molecular mechanism underlying variable apoptotic sensitivity of melanoma cells to MEK inhibition, we examined the expression and subcellular localization of Bcl-2 family members in a comprehensive set of human melanoma cell lines. Whereas the proapoptotic protein Bim was activated and localized to the mitochondrial membrane in all cell lines regardless of apoptotic sensitivity, Bmf activation and cytosolic translocation was exclusive to sensitive cells. In resistant cells, Bmf remained sequestered to the cytoskeleton through dynein light chain 2 (DLC2) binding. Overexpression of Bmf in resistant cells did not enhance apoptosis, whereas expression of mutant BmfA69P, which has decreased binding to DLC2, promoted cell death. Expression of BmfA69P mutants possessing the Bcl-2 homology 3 (BH3) domain mutation L138A, which impairs BH3 interactions, did not enhance apoptosis in resistant cells. RNA interference targeting Bim and Bmf provided protection from apoptosis induced by MEK inhibition. These results show a novel role for Bmf in promoting apoptosis and provide insight into the mechanism of apoptotic resistance to MEK inhibition in melanoma.

Engineering of chaperone systems and of the unfolded protein response

Production of recombinant proteins in mammalian cells is a successful technology that delivers protein pharmaceuticals for therapies and for diagnosis of human disorders. Cost effective production of protein biopharmaceuticals requires extensive optimization through cell and fermentation process engineering at the upstream and chemical engineering of purification processes at the downstream side of the production process. The majority of protein pharmaceuticals are secreted proteins. Accumulating evidence suggests that the folding and processing of these proteins in the endoplasmic reticulum (ER) is a general rate- and yield limiting step for their production. We will summarize our knowledge of protein folding in the ER and of signal transduction pathways activated by accumulation of unfolded proteins in the ER, collectively called the unfolded protein response (UPR). On the basis of this knowledge we will evaluate engineering approaches to increase cell specific productivities through engineering of the ER-resident protein folding machinery and of the UPR.

Physiological functions of Atg6/Beclin 1: a unique autophagy-related protein

The most striking morphological feature of eukaryotic cells is the presence of various membrane-enclosed compartments. These compartments, including organelles and transient transport intermediates, are not static. Rather, dynamic exchange of proteins and membrane is needed to maintain cellular homeostasis. One of the most dramatic examples of membrane mobilization is seen during the process of macroautophagy. Macroautophagy is the primary cellular pathway for degradation of long-lived proteins and organelles. In response to environmental cues, such as starvation or other types of stress, the cell produces a unique membrane structure, the phagophore. The phagophore sequesters cytoplasm as it forms a double-membrane cytosolic vesicle, an autophagosome. Upon completion, the autophagosome fuses with a lysosome or a vacuole in yeast, which delivers hydrolases that break down the inner autophagosome membrane along with its cargo, and the resulting macromolecules are released back into the cytosol for reuse. Autophagy is therefore a recycling process, allowing cells to survive periods of nutrient limitation; however, it has a wider physiological role, participating in development and aging, and also in protection against pathogen invasion, cancer and certain neurodegenerative diseases. In many cases, the role of autophagy is identified through studies of an autophagy-related protein, Atg6/Beclin 1. This protein is part of a lipid kinase complex, and recent studies suggest that it plays a central role in coordinating the cytoprotective function of autophagy and in opposing the cellular death process of apoptosis. Here, we summarize our current knowledge of Atg6/Beclin 1 in different model organisms and its unique function in the cell.

Suppression of cFLIP is sufficient to sensitize human melanoma cells to TRAIL- and CD95L-mediated apoptosis

Death ligands such as tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) and certain forms of CD95L are attractive therapeutic options for metastatic melanoma. Since knowledge about the regulation of death receptor sensitivity in melanoma is sparse, we have analysed these signaling pathways in detail. The loss of CD95 or TRAIL-R1, but not of TRAIL-R2, surface expression correlated with apoptosis sensitivity in a panel of melanoma cell lines. In contrast, the expression of proteins of the apical apoptosis signaling cascade (FADD, initiator caspases-8 and cFLIP) did not predict apoptosis sensitivity. Since both TRAIL-R1 and -R2 transmit apoptotic signals, we asked whether cFLIP, highly expressed in several of the cell lines tested, is sufficient to maintain resistance to TRAIL-R2-mediated apoptosis. Downregulation of cFLIP in TRAIL-R2-positive, TRAIL-resistant IGR cells dramatically increased TRAIL sensitivity. Conversely ectopic expression of cFLIP in TRAIL-sensitive, TRAIL-R2-expressing RPM-EP melanoma cells inhibited TRAIL- and CD95L-mediated cell death. Thus, modulation of cFLIP is sufficient to sensitize TRAIL-R2-expressing cells for TRAIL. Taken together, albeit expressing all proteins necessary for death receptor-mediated apoptosis, TRAIL-R1 negative melanoma cells cannot undergo TRAIL- or CD95L-induced apoptosis due to expression of cFLIP. Hence, cFLIP represents an attractive therapeutic target for melanoma treatment, especially in combination with TRAIL receptor agonists.