Cellular caspase-8-like inhibitory protein (cFLIP) prevents inhibition of muscle cell differentiation induced by cancer cells

Exploring association of melanoma-specific Bcl-xL with tumor immune microenvironment

BACKGROUND

Macrophages take center stage in the tumor microenvironment, a niche composed of extracellular matrix and a heterogeneous group of cells, including immune ones. They can evolve during tumor progression and acquire Tumor-Associated Macrophage (TAMs) phenotype. The release of cytokines by tumor and stromal cells, influence the secretion of cytokines by TAMs, which can guarantee tumor progression and influence the response to therapy. Among all factors able to recruit and polarize macrophages, we focused our attention on Bcl-xL, a multifaceted member of the Bcl-2 family, whose expression is deregulated in melanoma. It acts not only as a canonical pro-survival and anti-apoptotic protein, but also as a promoter of tumor progression.

METHODS

Human melanoma cells silencing or overexpressing Bcl-xL protein, THP-1 monocytic cells and monocyte-derived macrophages were used in this study. Protein array and specific neutralizing antibodies were used to analyze cytokines and chemokines secreted by melanoma cells. qRT-PCR, ELISA and Western Blot analyses were used to evaluate macrophage polarization markers and protein expression levels. Transwell chambers were used to evaluate migration of THP-1 and monocyte-derived macrophages. Mouse and zebrafish models were used to evaluate the ability of melanoma cells to recruit and polarize macrophages in vivo.

RESULTS

We demonstrated that melanoma cells overexpressing Bcl-xL recruit macrophages at the tumor site and induce a M2 phenotype. In addition, we identified that interleukin-8 and interleukin-1β cytokines are involved in macrophage polarization, and the chemokine CCL5/RANTES in the macrophages recruitment at the tumor site. We also found that all these Bcl-xL-induced factors are regulated in a NF-kB dependent manner in human and zebrafish melanoma models.

CONCLUSIONS

Our findings confirmed the pro-tumoral function of Bcl-xL in melanoma through its effects on macrophage phenotype.

C/EBPβ promotes the expression of atrophy-inducing factors by tumours and is a central regulator of cancer cachexia

BACKGROUND

CCAAT/enhancer-binding protein β (C/EBPβ) is a transcription factor whose high expression in human cancers is associated with tumour aggressiveness and poor outcomes. Most advanced cancer patients will develop cachexia, characterized by loss of skeletal muscle mass. In response to secreted factors from cachexia-inducing tumours, C/EBPβ is stimulated in muscle, leading to both myofibre atrophy and the inhibition of muscle regeneration. Involved in the regulation of immune responses, C/EBPβ induces the expression of many secreted factors, including cytokines. Because tumour-secreted factors drive cachexia and aggressive tumours have higher expression of C/EBPβ, we examined a potential role for C/EBPβ in the expression of tumour-derived cachexia-inducing factors.

METHODS

We used gain-of-function and loss-of-function approaches in vitro and in vivo to evaluate the role of tumour C/EBPβ expression on the secretion of cachexia-inducing factors.

RESULTS

We report that C/EBPβ overexpression up-regulates the expression of 260 secreted protein genes, resulting in a secretome that inhibits myogenic differentiation (-31%, P < 0.05) and myotube maturation [-38% (fusion index) and -25% (myotube diameter), P < 0.05]. We find that knockdown of C/EBPβ in cachexia-inducing Lewis lung carcinoma cells restores myogenic differentiation (+25%, P < 0.0001) and myotube diameter (+90%, P < 0.0001) in conditioned medium experiments and, in vivo, prevents muscle wasting (-51% for small myofibres vs. controls, P < 0.01; +140% for large myofibres, P < 0.01). Conversely, overexpression of C/EBPβ in non-cachectic tumours converts their secretome into a cachexia-inducing one, resulting in reduced myotube diameter (-41%, P < 0.0001, EL4 model) and inhibition of differentiation in culture (-26%, P < 0.01, EL4 model) and muscle wasting in vivo (+98% small fibres, P < 0.001; -76% large fibres, P < 0.001). Comparison of the differently expressed transcripts coding for secreted proteins in C/EBPβ-overexpressing myoblasts with the secretome from 27 different types of human cancers revealed ~18% similarity between C/EBPβ-regulated secreted proteins and those secreted by highly cachectic tumours (brain, pancreatic, and stomach cancers). At the protein level, we identified 16 novel secreted factors that are present in human cancer secretomes and are up-regulated by C/EBPβ. Of these, we tested the effect of three factors (SERPINF1, TNFRSF11B, and CD93) on myotubes and found that all had atrophic potential (-33 to -36% for myotube diameter, P < 0.01).

CONCLUSIONS

We find that C/EBPβ is necessary and sufficient to induce the secretion of cachexia-inducing factors by cancer cells and loss of C/EBPβ in tumours attenuates muscle atrophy in an animal model of cancer cachexia. Our findings establish C/EBPβ as a central regulator of cancer cachexia and an important therapeutic target.

A combination of sorafenib and radiotherapy reduces NF-κB activity and growth of hepatocellular carcinoma in an orthotopic mouse model

Hepatocellular carcinoma (HCC) is difficult to diagnose at an early stage, and its prognosis is generally poor. Sorafenib is the primary treatment for unresectable advanced HCC and targets multiple receptor tyrosine kinases. However, sorafenib only extends the average survival time by 3 months. This observation indicates that sorafenib may need to be combined with other treatments to further improve outcomes. We previously showed that combination of sorafenib with radiotherapy (RT) enhances tumor inhibition in subcutaneous HCC mouse models compared with monotherapy. The present study demonstrated that combining sorafenib and RT could suppress tumor growth in an orthotopic HCC model by regulating apoptosis and NF-κB-related pathways. Moreover, decreased numbers of visible liver tumors and a smaller percentage of spleen metastases were found in the combination group. A transient drop in body weight was initially observed after RT, but progressive recovery of body weight occurred. The current study showed that the combination of sorafenib and RT could be a safe strategy for HCC treatment.

CCAAT/Enhancer Binding Protein β inhibits myogenic differentiation via ID3

Myogenesis is regulated by the coordinated expression of muscle regulatory factors, a family of transcription factors that includes MYOD, MYF5, myogenin and MRF4. Muscle regulatory factors are basic helix-loop-helix transcription factors that heterodimerize with E proteins to bind the regulatory regions of target genes. Their activity can be inhibited by members of the Inhibitor of DNA binding and differentiation (ID) family, which bind E-proteins with high affinity, thereby preventing muscle regulatory factor-dependent transcriptional responses. CCAAT/Enhancer Binding protein beta (C/EBPβ) is a transcription factor expressed in myogenic precursor cells that acts to inhibit myogenic differentiation, though the mechanism remains poorly understood. We identify Id3 as a novel C/EBPβ target gene that inhibits myogenic differentiation. Overexpression of C/EBPβ stimulates Id3 mRNA and protein expression, and is required for C/EBPβ-mediated inhibition of myogenic differentiation. Misexpression of C/EBPβ in myogenic precursors, such as in models of cancer cachexia, prevents the differentiation of myogenic precursors and we show that loss of Id3 rescues differentiation under these conditions, suggesting that the stimulation of Id3 expression by C/EBPβ is an important mechanism by which C/EBPβ inhibits myogenic differentiation.

Expression of CCAAT/Enhancer Binding Protein Beta in Muscle Satellite Cells Inhibits Myogenesis in Cancer Cachexia

Cancer cachexia is a paraneoplastic syndrome that causes profound weight loss and muscle mass atrophy and is estimated to be the cause of up to 30% of cancer deaths. Though the exact cause is unknown, patients with cancer cachexia have increased muscle protein catabolism. In healthy muscle, injury activates skeletal muscle stem cells, called satellite cells, to differentiate and promote regeneration. Here, we provide evidence that this mechanism is inhibited in cancer cachexia due to persistent expression of CCAAT/Enhancer Binding Protein beta (C/EBPβ) in muscle myoblasts. C/EBPβ is a bzip transcription factor that is expressed in muscle satellite cells and is normally downregulated upon differentiation. However, in myoblasts exposed to a cachectic milieu, C/EBPβ expression remains elevated, despite activation to differentiate, resulting in the inhibition of myogenin expression and myogenesis. In vivo, cancer cachexia results in increased number of Pax7+ cells that also express C/EBPβ and the inhibition of normal repair mechanisms. Loss of C/EBPβ expression in primary myoblasts rescues differentiation under cachectic conditions without restoring myotube size, indicating that C/EBPβ is an important inhibitor of myogenesis in cancer cachexia.

Retinoid X Receptor-selective Signaling in the Regulation of Akt/Protein Kinase B Isoform-specific Expression

The differentiation and fusion of myoblasts into mature myotubes are complex processes responding to multiple signaling pathways. The function of Akt/PKB is critical for myogenesis, but less is clear as to the regulation of its isoform-specific expression. Bexarotene is a drug already used clinically to treat cancer, and it has the ability to enhance the commitment of embryonic stem cells into skeletal muscle lineage. Whereas bexarotene regulates fundamental biological processes through retinoid X receptor (RXR)-mediated gene expression, molecular pathways underlying its positive effects on myogenesis remain unclear. In this study, we have examined the signaling pathways that transmit bexarotene action in the context of myoblast differentiation. We show that bexarotene promotes myoblast differentiation and fusion through the activation of RXR and the regulation of Akt/PKB isoform-specific expression. Interestingly, bexarotene signaling appears to correlate with residue-specific histone acetylation and is able to counteract the detrimental effects of cachectic factors on myogenic differentiation. We also signify an isoform-specific role for Akt/PKB in RXR-selective signaling to promote and to retain myoblast differentiation. Taken together, our findings establish the viability of applying bexarotene in the prevention and treatment of muscle-wasting disorders, particularly given the lack of drugs that promote myogenic differentiation available for potential clinical applications. Furthermore, the model of bexarotene-enhanced myogenic differentiation will provide an important avenue to identify additional genetic targets and specific molecular interactions that we can study and apply for the development of potential therapeutics in muscle regeneration and repair.

NF-κB-activating complex engaged in response to EGFR oncogene inhibition drives tumor cell survival and residual disease in lung cancer

Although oncogene-targeted therapy often elicits profound initial tumor responses in patients, responses are generally incomplete because some tumor cells survive initial therapy as residual disease that enables eventual acquired resistance. The mechanisms underlying tumor cell adaptation and survival during initial therapy are incompletely understood. Here, through the study of EGFR mutant lung adenocarcinoma, we show that NF-κB signaling is rapidly engaged upon initial EGFR inhibitor treatment to promote tumor cell survival and residual disease. EGFR oncogene inhibition induced an EGFR-TRAF2-RIP1-IKK complex that stimulated an NF-κB-mediated transcriptional survival program. The direct NF-κB inhibitor PBS-1086 suppressed this adaptive survival program and increased the magnitude and duration of initial EGFR inhibitor response in multiple NSCLC models, including a patient-derived xenograft. These findings unveil NF-κB activation as a critical adaptive survival mechanism engaged by EGFR oncogene inhibition and provide rationale for EGFR and NF-κB co-inhibition to eliminate residual disease and enhance patient responses.

Boron nitride nanotube-mediated stimulation of cell co-culture on micro-engineered hydrogels

In this paper, we describe the effects of the combination of topographical, mechanical, chemical and intracellular electrical stimuli on a co-culture of fibroblasts and skeletal muscle cells. The co-culture was anisotropically grown onto an engineered micro-grooved (10 µm-wide grooves) polyacrylamide substrate, showing a precisely tuned Young’s modulus (∼ 14 kPa) and a small thickness (∼ 12 µm). We enhanced the co-culture properties through intracellular stimulation produced by piezoelectric nanostructures (i.e., boron nitride nanotubes) activated by ultrasounds, thus exploiting the ability of boron nitride nanotubes to convert outer mechanical waves (such as ultrasounds) in intracellular electrical stimuli, by exploiting the direct piezoelectric effect. We demonstrated that nanotubes were internalized by muscle cells and localized in both early and late endosomes, while they were not internalized by the underneath fibroblast layer. Muscle cell differentiation benefited from the synergic combination of topographical, mechanical, chemical and nanoparticle-based stimuli, showing good myotube development and alignment towards a preferential direction, as well as high expression of genes encoding key proteins for muscle contraction (i.e., actin and myosin). We also clarified the possible role of fibroblasts in this process, highlighting their response to the above mentioned physical stimuli in terms of gene expression and cytokine production. Finally, calcium imaging-based experiments demonstrated a higher functionality of the stimulated co-cultures.

Sarcopenia and cachexia: the adaptations of negative regulators of skeletal muscle mass

Recent advances in our understanding of the biology of muscle, and how anabolic and catabolic stimuli interact to control muscle mass and function, have led to new interest in the pharmacological treatment of muscle wasting. Loss of muscle occurs as a consequence of several chronic diseases (cachexia) as well as normal aging (sarcopenia). Although many negative regulators [Atrogin-1, muscle ring finger-1, nuclear factor-kappaB (NF-κB), myostatin, etc.] have been proposed to enhance protein degradation during both sarcopenia and cachexia, the adaptation of mediators markedly differs among these conditions. Sarcopenic and cachectic muscles have been demonstrated to be abundant in myostatin- and apoptosis-linked molecules. The ubiquitin-proteasome system (UPS) is activated during many different types of cachexia (cancer cachexia, cardiac heart failure, chronic obstructive pulmonary disease), but not many mediators of the UPS change during sarcopenia. NF-κB signaling is activated in cachectic, but not in sarcopenic, muscle. Some studies have indicated a change of autophagic signaling during both sarcopenia and cachexia, but the adaptation remains to be elucidated. This review provides an overview of the adaptive changes in negative regulators of muscle mass in both sarcopenia and cachexia.

Polyamidoamine dendrimer nanoparticle cytotoxicity, oxidative stress, caspase activation and inflammatory response: experimental observation and numerical simulation

Mechanisms underlying the in vitro cytotoxicity of Polyamidoamine nano-dendrimers in human keratinocytes are explored. Previous studies demonstrated a systematic, dendrimer-generation-dependent cytotoxicity, oxidative stress, and genotoxicity. The emerging picture is of dendrimer endocytosis, endosomal rupture and subsequent mitochondrial attack and cell death. To understand the underlying mechanisms, the evolution of reactive oxygen species, intracellular glutathione, caspase activation, mitochondrial membrane potential decay, and inflammatory responses have been examined. Early-stage responses are associated with endosomal encapsulation, later-stage with mitochondrial attack. In all cases, the magnitude and evolution of responses depend on dendrimer generation and dose. The early-stage response is modelled using a rate equation approach, qualitatively reproducing the time, dose and generation dependences, using only two variable parameters. The dependence of the response on the nanoparticle physicochemical properties can thus be separated from internal cellular parameters, and responses can be quantified in terms of rate constants rather than commonly employed effective concentrations.

FROM THE CLINICAL EDITOR

This contribution reports on the intracellular mechanism of PAMAM dendrimer cytotoxicity in human keratinocytes. In all cases, the magnitude and evolution of responses depend on dendrimer generation and dose. Experimental data were supported by numerical simulation using only two variables. It is suggested that responses can be quantified in terms of rate constants rather than effective concentrations.

Deubiquitinating enzyme A20 negatively regulates NF-κB signaling in skeletal muscle in mdx mice

Duchenne muscular dystrophy (DMD) is caused by the lack of a functional dystrophin protein that results in muscle fiber membrane disruption and, ultimately, degeneration. Regeneration of muscle fibers fails progressively, and muscle tissue is replaced with connective tissue. As a result, DMD causes progressive limb muscle weakness and cardiac and respiratory failure. The absence of dystrophin from muscle fibers triggers the chronic activation of the nuclear factor of kappa B (NF-κB). Chronic activation of NF-κB in muscle leads to infiltration of macrophages, up-regulation of the ubiquitin-proteosome system, and down-regulation of the helix-loop-helix muscle regulatory factor, MyoD. These processes, triggered by NF-κB activation, promote muscle degeneration and failure of muscle regeneration. A20 (TNFAIP3) is a critical negative regulator of NF-κB. In this study, we characterize the role of A20 in regulating NF-κB activation in skeletal muscle, identifying a novel role in muscle regeneration. A20 is highly expressed in regenerating muscle fibers, and knockdown of A20 impairs muscle differentiation in vitro, which suggests that A20 expression is critically important for regeneration of dystrophic muscle tissue. Furthermore, down-regulation of the classic pathway of NF-κB activation is associated with up-regulation of the alternate pathway in regenerating muscle fibers, suggesting a mechanism by which A20 promotes muscle regeneration. These results demonstrate the important role of A20 in muscle fiber repair and suggest the potential of A20 as a therapeutic target to ameliorate the pathology and clinical symptoms of DMD.

High-content drug screening with engineered musculoskeletal tissues

Tissue engineering for in vitro drug-screening applications based on tissue function is an active area of translational research. Compared to targeted high-throughput drug-screening methods that rapidly analyze hundreds of thousands of compounds affecting a single biochemical reaction or gene expression, high-content screening (HCS) with engineered tissues is more complex and based on the cumulative positive and negative effects of a compound on the multiple pathways altering tissue function. It may therefore serve as better predictor of in vivo activity and serve as a bridge between high-throughput drug screening and in vivo animal studies. In the case of the musculoskeletal system, tissue function includes determining improvements in the mechanical properties of bone, tendon, cartilage, and, for skeletal muscle, contractile properties such as rate of contraction/relaxation, force generation, fatigability, and recovery from fatigue. HCS of compound banks with engineered tissues requires miniature musculoskeletal organs as well as automated functional testing. The resulting technologies should be rapid, cost effective, and reduce the number of small animals required for follow-on in vivo studies. Identification of compounds that improve the repair/regeneration of damaged tissues in vivo would have extensive clinical applications for treating musculoskeletal disorders.

Apoptosis and tumor resistance conferred by Par-4

Par-4 is a tumor suppressor protein with a pro-apoptotic function. Epigenetic silencing of Par-4 is seen in diverse tumors and Par-4 knockout mice develop spontaneous tumors in various tissues. Endogenous Par-4 is essential for sensitization of cells to diverse apoptotic stimuli, whereas ectopic expression of Par-4 can selectively induce apoptosis in cancer cells. The cancer-specific pro-apoptotic action of Par-4 resides in its centrally located SAC domain. This review emphasizes the role of Par-4/SAC in apoptosis and tumor resistance. SAC transgenic mice display normal development and life span, and, most importantly, are resistant to spontaneous, as well as oncogene-induced, autochthonous tumors. The tumor resistant phenotype and undetectable toxicity of SAC in vivo suggests the SAC domain possesses tremendous therapeutic potential.

Involvement of nuclear factor-kappa B in bcl-xL-induced interleukin 8 expression in glioblastoma

We recently reported that bcl-xL regulates interleukin 8 (CXCL8) protein expression and promoter activity in glioblastoma cells. In this paper we demonstrate that CXCL8 induction by bcl-xL is mediated through a nuclear factor-kappa B (NF-kB)-dependent mechanism. Mutational studies on the CXCL8 promoter showed that NF-kB binding site was required for bcl-xL-induced promoter activity and an enhanced nuclear expression of NF-kB subunits p65 and p50 was observed after bcl-xL over-expression. Electrophoretic mobility shift assay showed an increased DNA-binding activity of NF-kB in bcl-xL over-expressing cells and the use of specific antibodies confirmed the involvement of p65 and p50 in NF-kB activity on CXCL8 promoter sequence. NF-kB activity regulation by bcl-xL involved IkBalpha and IKK complex signaling pathway. In fact, bcl-xL over-expression induced a decrease of cytoplasmic expression of the IkBalpha protein, paralleled by an increase in the phosphorylation of the same IkBalpha and IKKalpha/beta. Moreover, the down-regulation of the ectopic or endogenous bcl-xL expression through RNA interference confirmed the ability of bcl-xL to modulate NF-kB pathway, and the transient expression of a degradation-resistant form of the cytoplasmic NF-kB inhibitor IkBalpha in bcl-xL transfectants confirmed the involvement of that inhibitor in bcl-xL-induced CXCL8 expression and promoter activity. In conclusion, our results demonstrate the role of NF-kB as the mediator of bcl-xL-induced CXCL8 up-regulation in glioblastoma cells.

Nuclear factor-kappa B signaling in skeletal muscle atrophy

Skeletal muscle atrophy/wasting is a serious complication of a wide range of diseases and conditions such as aging, disuse, AIDS, chronic obstructive pulmonary disease, space travel, muscular dystrophy, chronic heart failure, sepsis, and cancer. Emerging evidence suggests that nuclear factor-kappa B (NF-kappaB) is one of the most important signaling pathways linked to the loss of skeletal muscle mass in various physiological and pathophysiological conditions. Activation of NF-kappaB in skeletal muscle leads to degradation of specific muscle proteins, induces inflammation and fibrosis, and blocks the regeneration of myofibers after injury/atrophy. Recent studies employing genetic mouse models have provided strong evidence that NF-kappaB can serve as an important molecular target for the prevention of skeletal muscle loss. In this article, we have outlined the current understanding regarding the role of NF-kappaB in skeletal muscle with particular reference to different models of muscle wasting and the development of novel therapy.

Drug-screening platform based on the contractility of tissue-engineered muscle

A tissue-based approach to in vitro drug screening allows for determination of the cumulative positive and negative effects of a drug at the tissue rather than the cellular or subcellular level. Skeletal muscle myoblasts were tissue-engineered into three-dimensional muscle with parallel myofibers generating directed forces. When grown attached to two flexible micro-posts (mu posts) acting as artificial tendons in a 96-well plate format, the miniature bioartificial muscles (mBAMs) generated tetanic (active) forces upon electrical stimulation measured with a novel image-based motion detection system. mBAM myofiber hypertrophy and active force increased in response to insulin-like growth factor 1. In contrast, mBAM deterioration and weakness was observed with a cholesterol-lowering statin. The results described in this study demonstrate the integration of tissue engineering and biomechanical testing into a single platform for the screening of compounds affecting muscle strength.