A retrovirus-based system to stably silence GDF-8 expression and enhance myogenic differentiation in human rhabdomyosarcoma cells

Two Activin Type 2B Receptors from Sea Bream Function Similarly in vitro

Myostatin (MSTN) and activin are members of the transforming growth factor-β superfamily. Both signal through the activin type II receptors (ActRII and ActRIIB). In a previous report, we demonstrated that fish possess at least 2 genes for ActRIIB: ActRIIB-1 and ActRIIB-2, which differ in their amino acid sequence. We also showed that affinity-purified, fish-soluble ActRIIB-1 (extracellular domain; ECD), produced in the yeast Pichia pastoris, inhibited recombinant mouse/rat/human mature MSTN activity in vitro using a reporter gene assay in the mammalian A204 cell line. In the present study, we produced soluble ActRIIB-2a in P. pastoris, and showed that it is N-glycosylated, similar to soluble ActRIIB-1. Inhibition of MSTN and activin A activities by affinity-purified ActRIIB-2a was compared with that of soluble ActRIIB-1 using the CAGA-luciferase assay in A204 cells. The findings of this study provide evidence that both paralogs, which probably resulted from gene duplication, did not diversify in their functionality (neofunctionalization), but rather retained a similar function. Both ActRIIB isoforms are equally potent in the mammalian system, and both exhibited an inhibitory effect on mammalian MSTN and activin A. Moreover--in spite of the amino acid differences in ECD between the two paralogs--it appears that the residues important for ligand binding are conserved, and that they recognize the mammalian ligands activin A and MSTN to the same extent.

The importance of being dead: cell death mechanisms assessment in anti-sarcoma therapy

Cell death can occur through different mechanisms, defined by their nature and physiological implications. Correct assessment of cell death is crucial for cancer therapy success. Sarcomas are a large and diverse group of neoplasias from mesenchymal origin. Among cell death types, apoptosis is by far the most studied in sarcomas. Albeit very promising in other fields, regulated necrosis and other cell death circumstances (as so-called "autophagic cell death" or "mitotic catastrophe") have not been yet properly addressed in sarcomas. Cell death is usually quantified in sarcomas by unspecific assays and in most cases the precise sequence of events remains poorly characterized. In this review, our main objective is to put into context the most recent sarcoma cell death findings in the more general landscape of different cell death modalities.

Local overexpression of the myostatin propeptide increases glucose transporter expression and enhances skeletal muscle glucose disposal

Insulin resistance (IR) in skeletal muscle is a prerequisite for type 2 diabetes and is often associated with obesity. IR also develops alongside muscle atrophy in older individuals in sarcopenic obesity. The molecular defects that underpin this syndrome are not well characterized, and there is no licensed treatment. Deletion of the transforming growth factor-β family member myostatin, or sequestration of the active peptide by overexpression of the myostatin propeptide/latency-associated peptide (ProMyo) results in both muscle hypertrophy and reduced obesity and IR. We aimed to establish whether local myostatin inhibition would have a paracrine/autocrine effect to enhance glucose disposal beyond that simply generated by increased muscle mass, and the mechanisms involved. We directly injected adeno-associated virus expressing ProMyo in right tibialis cranialis/extensor digitorum longus muscles of rats and saline in left muscles and compared the effects after 17 days. Both test muscles were increased in size (by 7 and 11%) and showed increased radiolabeled 2-deoxyglucose uptake (26 and 47%) and glycogen storage (28 and 41%) per unit mass during an intraperitoneal glucose tolerance test. This was likely mediated through increased membrane protein levels of GLUT1 (19% higher) and GLUT4 (63% higher). Interestingly, phosphorylation of phosphoinositol 3-kinase signaling intermediates and AMP-activated kinase was slightly decreased, possibly because of reduced expression of insulin-like growth factor-I in these muscles. Thus, myostatin inhibition has direct effects to enhance glucose disposal in muscle beyond that expected of hypertrophy alone, and this approach may offer potential for the therapy of IR syndromes.

Knockdown of endogenous myostatin promotes sheep myoblast proliferation

Myostatin (MSTN), is a known negative regulator of myogenesis. Silencing of the function of MSTN could result in increasing muscle mass in mice. To determine the function of endogenous MSTN expression on proliferation of sheep myoblasts, a short-hairpin RNA-targeting sheep MSTN was constructed into lentiviral vector to silence endogenous MSTN expression. We demonstrated that silencing of endogenous MSTN gene with up to approximately 73.3% reduction by short hairpin RNA (shRNA) resulted in significant increase (overall 28.3%) of proliferation of primary ovine myoblasts. The upregulation of proliferation was accompanied by the decrease expression of MyoD (-37.6%, p = 0.025), myogenin (-33.1%, p = 0.049), p21 (-49.3%, p = 0.046), and Smad3 (-50.0%, p = 0.007). Silencing of myostatin using shRNA may provide a feasible approach to improve meat productivity in farm animals.

Inhibition of hepatitis B virus (HBV) gene expression and replication by HBx gene silencing in a hydrodynamic injection mouse model with a new clone of HBV genotype B

Background

It has been suggested that different hepatitis B virus (HBV) genotypes may have distinct virological characteristics that correlate with clinical outcomes during antiviral therapy and the natural course of infection. Hydrodynamic injection (HI) of HBV in the mouse model is a useful tool for study of HBV replication in vivo. However, only HBV genotype A has been used for studies with HI.

Methods

We constructed 3 replication-competent clones containing 1.1, 1.2 and 1.3 fold overlength of a HBV genotype B genome and tested them both in vitro and in vivo. Moreover, A HBV genotype B clone based on the pAAV-MCS vector was constructed with the 1.3 fold HBV genome, resulting in the plasmid pAAV-HBV1.3_B and tested by HI in C57BL/6 mice. Application of siRNA against HBx gene was tested in HBV genotype B HI mouse model.

Results

The 1.3 fold HBV clone showed higher replication and gene expression than the 1.1 and 1.2 fold HBV clones. Compared with pAAV-HBV1.2 (genotype A), the mice HI with pAAV-HBV1.3_B showed higher HBsAg and HBeAg expression as well as HBV DNA replication level but a higher clearance rate. Application of two plasmids pSB-HBxi285 and pSR-HBxi285 expressing a small/short interfering RNA (siRNA) to the HBx gene in HBV genotype B HI mouse model, leading to an inhibition of HBV gene expression and replication. However, HBV gene expression may resume in some mice despite an initial delay, suggesting that transient suppression of HBV replication by siRNA may be insufficient to prevent viral spread, particularly if the gene silencing is not highly effective.

Conclusions

Taken together, the HI mouse model with a HBV genotype B genome was successfully established and showed different characteristics in vivo compared with the genotype A genome. The effectiveness of gene silencing against HBx gene determines whether HBV replication may be sustainably inhibited by siRNA in vivo.

Selection of an effective small interference RNA to silence myostatin gene expression in sheep fibroblast cells

Myostatin (MSTN), a member of the TGF-β superfamily, has been identified as a negative regulator of skeletal muscle mass. Inactivating mutations in the MSTN gene are responsible for the development of a hypermuscular phenotype. The aim of this study was to identify an effective small interfering RNA (siRNA) to knockdown the myostatin gene in sheep fibroblast cells. Four siRNAs targeting sheep myostatin were synthesized and tested. Quantitative RT-PCR showed that siRNA1, siRNA2, siRNA3, and siRNA5 significantly reduced myostatin transcript levels by 72, 68, 56, and 76 % (P < 0.05), respectively. Western blot analysis showed that myostatin protein expression was significantly reduced by 76 % using siRNA1 and by 65 % using siRNA5 (P < 0.05). Therefore, siRNA1 and siRNA5 may have the potential to knockdown myostatin gene expression and increase sheep meat production, which should be a focus of future studies.

Caveolins in rhabdomyosarcoma

Caveolins are scaffolding proteins that play a pivotal role in numerous processes, including caveolae biogenesis, vesicular transport, cholesterol homeostasis and regulation of signal transduction. There are three different isoforms (Cav-1, -2 and -3) that form homo- and hetero-aggregates at the plasma membrane and modulate the activity of a number of intracellular binding proteins. Cav-1 and Cav-3, in particular, are respectively expressed in the reserve elements (e.g. satellite cells) and in mature myofibres of skeletal muscle and their expression interplay characterizes the switch from muscle precursors to differentiated elements. Recent findings have shown that caveolins are also expressed in rhabdomyosarcoma, a group of heterogeneous childhood soft-tissue sarcomas in which the cancer cells seem to derive from progenitors that resemble myogenic cells. In this review, we will focus on the role of caveolins in rhabdomyosarcomas and on their potential use as markers of the degree of differentiation in these paediatric tumours. Given that the function of Cav-1 as tumour conditional gene in cancer has been well-established, we will also discuss the relationship between Cav-1 and the progression of rhabdomyosarcoma.

Differentiation of human rhabdomyosarcoma RD cells is regulated by reciprocal, functional interactions between myostatin, p38 and extracellular regulated kinase signalling pathways

Rhabdomyosarcoma (RMS) includes heterogeneous tumours of mesenchymal derivation which are genetically committed to the myogenic lineage, but fail to complete terminal differentiation. Previous works have reported on deregulated myostatin, p38 and extracellular regulated kinase (ERK) signalling in RMS cell lines; however, the functional link between these pathways and their relative contribution to RMS pathogenesis and/or maintenance of the transformed phenotype in vitro are unclear. Herein we show that the constitutive expression of a dominant-negative form of activin receptor type IIb (dnACTRIIb), which inhibits myostatin signalling, decreased proliferation and promoted differentiation of the human RMS RD cell line. DnACTRIIb-dependent differentiation of RD cells correlated with a reduced SMAD2/3 (small mother against decapentaplegic) and ERK signalling and the activation of p38 pathway. Conversely, the expression of a constitutively activated ALK5 (activin receptor-like kinase) (caALK5) form, activating SMAD3 and ERK pathways, led to further impairment of RD differentiation. Pharmacological blockade of ERK pathway in RD cells was sufficient to replicate the biological phenotype observed in dnACTRIIb-expressing RD cells, and also recovered the differentiation of caALK5-expressing RD cells. Conversely, deliberate activation of p38 signalling mimics the effect of dnActRIIb and overcame the differentiation block in RD cells. These data indicate the existence of a network formed by myostatin/SMAD2/3, ERK and p38 pathways that, when deregulated, might contribute to the pathogenesis of RMS. The components of this network might, therefore, be a valuable target for interventions towards correcting the malignant phenotype of RMS.

Gene knockdown with lentiviral vector-mediated intrathecal RNA interference of protein kinase C gamma reverses chronic morphine tolerance in rats

BACKGROUND

Although morphine is a widely used opioid analgesic, morphine tolerance (MT) has limited the use of the drug because it creates the necessity for high doses. Protein kinase C (PKC), especially the PKCγ isoform, is considered to play a key role in the development of MT. Because RNA interference provides a powerful method for the investigation of gene function, and lentiviral delivery systems have been approved for human use, this present study examined rats tolerant to morphine to determine whether an intrathecal injection of a lentiviral vector of PKCγ short hairpin RNA (LV-shPKCγ) down-regulated the expression of the PKCγ gene and reversed MT.

METHODS

MT was induced by intrathecal morphine (10 µg b.i.d.) for six consecutive days. A lentiviral-mediated short hairpin RNA (shRNA) system was synthesized to deliver the PKCγ shRNAs to the spinal cord of the rats with MT. Mechanical and thermal paw withdrawal threshold were assessed to determine the analgesic effects of morphine. Expression of PKCγ mRNA and protein was determined by reverse transcriptase-polymerase chain reaction and western blotting analysis, respectively.

RESULTS

The chronic administration of morphine induced a stabilized analgesic tolerance. A single injection of LV-shPKCγ significantly reversed morphine antinociceptive tolerance. Compared to the control group, PKCγ mRNA and protein levels were dramatically down-regulated in the LV-shPKCγ group.

CONCLUSIONS

A single injection of LV-shPKCγ reversed MT by reducing the expression of PKCγ in the spinal cord. These findings indicate that the use of LV-shPKCγ might be a potential strategy for therapy in MT.

Antisense-induced myostatin exon skipping leads to muscle hypertrophy in mice following octa-guanidine morpholino oligomer treatment

Myostatin is a negative regulator of muscle mass, and several strategies are being developed to knockdown its expression to improve muscle-wasting conditions. Strategies using antimyostatin-blocking antibodies, inhibitory-binding partners, signal transduction blockers, and RNA interference system (RNAi)-based knockdown have yielded promising results and increased muscle mass in experimental animals. These approaches have, however, a number of disadvantages such as transient effects or adverse immune complications. We report here the use of antisense oligonucleotides (AOs) to manipulate myostatin pre-mRNA splicing and knockdown myostatin expression. Both 2'O-methyl phosphorothioate RNA (2'OMePS) and phosphorodiamidate morpholino oligomers (PMO) led to efficient exon skipping in vitro and in vivo and knockdown of myostatin at the transcript level. The substantial myostatin exon skipping observed after systemic injection of Vivo-PMO into normal mice led to a significant increase in soleus muscle mass as compared to the controls injected with normal saline suggesting that this approach could be feasible to ameliorate muscle-wasting pathologies.

Molecular and cellular biology of rhabdomyosarcoma

Rhabdomyosarcoma is a group of soft-tissue sarcomas that share features of skeletal myogenesis, but show extensive heterogeneity in histology, age and site of onset, and prognosis. This review matches recent molecular data with biological features of rhabdomyosarcoma. Alterations in molecular pathways, animal models, cell of origin and potential new therapeutic targets are discussed.