Glycogen synthase kinase 3 inhibitors induce the canonical WNT/β-catenin pathway to suppress growth and self-renewal in embryonal rhabdomyosarcoma

Canonical Wnt signaling pathway contributes to the proliferation and survival in porcine pancreatic stem cells (PSCs)

Pancreatic stem cells (PSCs) transplantation is a potential therapeutic approach to type 1 diabetes mellitus (D1M). However, before clinical use, there are some major hurdles to be faced that need to be comprehensively considered and given some potential solutions in vitro. Human PSCs are difficult to obtain and have a short replicative senescence. As an alternative, we instead established porcine PSCs; as insulin is highly conserved and physiological glucose levels are similar between human and porcine. In order to solve the problems during transplantation therapy, such as the need for an enormous amount of PSCs and good cell survival in overactive autoimmunity induced by reactive oxygen cpecies (ROS) in D1M patients, we utilized Wnt3a overexpression to activate the canonical Wnt signaling pathway in PSCs. We found that the expression of proliferation genes, such as c-Myc, was up-regulated as the downstream of β-catenin, which promoted the PSCs proliferation and made cell numbers to meet the transplantation needs. We also showed that activation of the Wnt pathway made cells more readily tolerate ROS-caused mitochondria injury and cell apoptosis, thus making cells survive in autoimmune patients. The present study provides a theoretical basis for cell transplantation therapy of diabetes.

Secreted Frizzled-Related Protein 3 (SFRP3) Is Required for Tumorigenesis of PAX3-FOXO1-Positive Alveolar Rhabdomyosarcoma

PURPOSE

Rhabdomyosarcoma (RMS) is a soft tissue sarcoma associated with the skeletal muscle lineage. Of the two predominant subtypes, known as embryonal (eRMS) and alveolar (aRMS), aRMS has the poorer prognosis, with a five-year survival rate of <50%. The majority of aRMS tumors express the fusion protein PAX3-FOXO1. As PAX3-FOXO1 has proven chemically intractable, this study aims to identify targetable proteins that are downstream from or cooperate with PAX3-FOXO1 to support tumorigenesis.

EXPERIMENTAL DESIGN

Microarray analysis of the transcriptomes of human skeletal muscle myoblasts expressing PAX3-FOXO1 revealed alteration of several Wnt pathway gene members, including secreted frizzled related protein 3 (SFRP3), a secreted Wnt pathway inhibitor. Loss-of-function using shRNAs against SFRP3 was used to interrogate the role of SFRP3 in human aRMS cell lines in vitro and conditional murine xenograft systems in vivo. The combination of SFRP3 genetic suppression and the chemotherapeutic agent vincristine was also examined.

RESULTS

In vitro, suppression of SFRP3 inhibited aRMS cell growth, reduced proliferation accompanied by a G1 arrest and induction of p21, and induced apoptosis. In vivo, doxycycline-inducible suppression of SFRP3 reduced aRMS tumor growth and weight by more than three-fold, in addition to increasing myogenic differentiation and β-catenin signaling. The combination of SFRP3 suppression and vincristine was more effective at reducing aRMS cell growth in vitro than either treatment alone, and ablated tumorigenesis in vivo.

CONCLUSIONS

SFRP3 is necessary for the growth of human aRMS cells both in vitro and in vivo and is a promising new target for investigation in aRMS.

Inhibiting phosphorylation of the oncogenic PAX3-FOXO1 reduces alveolar rhabdomyosarcoma phenotypes identifying novel therapy options

Patients with translocation-positive alveolar rhabdomyosarcoma (ARMS), an aggressive childhood tumor primarily characterized by the PAX3-FOXO1 oncogenic fusion protein, have a poor prognosis because of lack of therapies that specifically target ARMS tumors. This fact highlights the need for novel pharmaceutical interventions. Posttranslational modifications such as phosphorylation are becoming attractive biological targets for the development of such interventions. Along these lines, we demonstrated that PAX3-FOXO1 is phosphorylated at three specific sites and that its pattern of phosphorylation is altered relative to wild-type Pax3 throughout early myogenesis and in ARMS tumor cells. However, little work has been performed examining the effect of directly inhibiting phosphorylation at these sites on ARMS development. To address this gap in knowledge, we used small molecule inhibitors or mutational analysis to specifically inhibit phosphorylation of PAX3-FOXO1 to investigate how altering phosphorylation of the oncogenic fusion protein affects ARMS phenotypes. We found that inhibiting the phosphorylation of PAX3-FOXO1 at Ser201 significantly reduced migration, invasion and proliferation in two independent ARMS tumor cell lines. Further, we found that inhibition of phosphorylation at Ser205 also decreased proliferation and anchorage-independent growth. Consistent with these in vitro results, we demonstrate for the first time that PAX3-FOXO1 is phosphorylated at Ser201 and Ser205 in a primary tumor sample and in tumor cells actively invading the surrounding normal tissue. This report is the first to demonstrate that the direct inhibition of PAX3-FOXO1 phosphorylation reduces ARMS tumor phenotypes in vitro and that these phosphorylation events are present in primary human ARMS tumors and invading tumor cells. These results identify phosphorylation of PAX3-FOXO1, especially at Ser201, as a novel biological target that can be explored as a promising avenue for ARMS therapies.

Zebrafish as a model to assess cancer heterogeneity, progression and relapse

Clonal evolution is the process by which genetic and epigenetic diversity is created within malignant tumor cells. This process culminates in a heterogeneous tumor, consisting of multiple subpopulations of cancer cells that often do not contain the same underlying mutations. Continuous selective pressure permits outgrowth of clones that harbor lesions that are capable of enhancing disease progression, including those that contribute to therapy resistance, metastasis and relapse. Clonal evolution and the resulting intratumoral heterogeneity pose a substantial challenge to biomarker identification, personalized cancer therapies and the discovery of underlying driver mutations in cancer. The purpose of this Review is to highlight the unique strengths of zebrafish cancer models in assessing the roles that intratumoral heterogeneity and clonal evolution play in cancer, including transgenesis, imaging technologies, high-throughput cell transplantation approaches and in vivo single-cell functional assays.

Pediatric Rhabdomyosarcoma

Rhabdomyosarcoma is the most common soft-tissue sarcoma of childhood, and despite clinical advances, subsets of these patients continue to suffer high levels of morbidity and mortality associated with their disease. Recent genetic and molecular characterization of these tumors using sophisticated genomics techniques, including next-generation sequencing experiments, has revealed multiple areas that can be exploited for new molecularly targeted therapies for this disease.

Normal and malignant muscle cell transplantation into immune compromised adult zebrafish

Zebrafish have become a powerful tool for assessing development, regeneration, and cancer. More recently, allograft cell transplantation protocols have been developed that permit engraftment of normal and malignant cells into irradiated, syngeneic, and immune compromised adult zebrafish. These models when coupled with optimized cell transplantation protocols allow for the rapid assessment of stem cell function, regeneration following injury, and cancer. Here, we present a method for cell transplantation of zebrafish adult skeletal muscle and embryonal rhabdomyosarcoma (ERMS), a pediatric sarcoma that shares features with embryonic muscle, into immune compromised adult rag2(E450fs) homozygous mutant zebrafish. Importantly, these animals lack T cells and have reduced B cell function, facilitating engraftment of a wide range of tissues from unrelated donor animals. Our optimized protocols show that fluorescently labeled muscle cell preparations from α-actin-RFP transgenic zebrafish engraft robustly when implanted into the dorsal musculature of rag2 homozygous mutant fish. We also demonstrate engraftment of fluorescent-transgenic ERMS where fluorescence is confined to cells based on differentiation status. Specifically, ERMS were created in AB-strain myf5-GFP; mylpfa-mCherry double transgenic animals and tumors injected into the peritoneum of adult immune compromised fish. The utility of these protocols extends to engraftment of a wide range of normal and malignant donor cells that can be implanted into dorsal musculature or peritoneum of adult zebrafish.

New insights into signalling-pathway alterations in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma in children and young adults. Several recent studies have shed new light on the alterations in signalling pathways and the downstream effects of these pathway alterations in RMS. Many of these effects converge on the fibroblast growth factor and insulin-like growth-factor pathways. These new findings improve the current understanding of RMS, thus offering novel potential therapeutic targets and strategies that may improve the outcome for patients with RMS.

YAPping about differentiation therapy in muscle cancer

Overcoming a presumed differentiation block in the childhood muscle cancer embryonal rhabdomyosarcoma is often thought to hold promise as an approach to replace cytotoxic chemotherapy with molecularly-targeted differentiation therapies. In this issue of Cancer Cell, Tremblay and colleagues implicate YAP1 and the Hippo signaling pathway in the maintenance of differentiation-arrested and proliferative phenotypes for embryonal rhabdomyosarcoma.