MYOD-SKP2 axis boosts tumorigenesis in fusion negative rhabdomyosarcoma by preventing differentiation through p57Kip2^{Kip2} targeting

Rhabdomyosarcomas (RMS) are pediatric mesenchymal-derived malignancies encompassing PAX3/7-FOXO1 Fusion Positive (FP)-RMS, and Fusion Negative (FN)-RMS with frequent RAS pathway mutations. RMS express the master myogenic transcription factor MYOD that, whilst essential for survival, cannot support differentiation. Here we discover SKP2, an oncogenic E3-ubiquitin ligase, as a critical pro-tumorigenic driver in FN-RMS. We show that SKP2 is overexpressed in RMS through the binding of MYOD to an intronic enhancer. SKP2 in FN-RMS promotes cell cycle progression and prevents differentiation by directly targeting p27$^{Kip1}$ and p57$^{Kip2}$, respectively. SKP2 depletion unlocks a partly MYOD-dependent myogenic transcriptional program and strongly affects stemness and tumorigenic features and prevents in vivo tumor growth. These effects are mirrored by the investigational NEDDylation inhibitor MLN4924. Results demonstrate a crucial crosstalk between transcriptional and post-translational mechanisms through the MYOD-SKP2 axis that contributes to tumorigenesis in FN-RMS. Finally, NEDDylation inhibition is identified as a potential therapeutic vulnerability in FN-RMS

ICAM-2 Expression Mediates a Membrane-Actin Link, Confers a Nonmetastatic Phenotype and Reflects Favorable Tumor Stage or Histology in Neuroblastoma

The actin cytoskeleton is a primary determinant of tumor cell motility and metastatic potential. Motility and metastasis are thought to be regulated, in large part, by the interaction of membrane proteins with cytoplasmic linker proteins and of these linker proteins, in turn, with actin. However, complete membrane-to-actin linkages have been difficult to identify. We used co-immunoprecipitation and competitive peptide assays to show that intercellular adhesion molecule-2 (ICAM-2)/α-actinin/actin may comprise such a linkage in neuroblastoma cells. ICAM-2 expression limited the motility of these cells and redistributed actin fibers in vitro, and suppressed development of disseminated tumors in an in vivo model of metastatic neuroblastoma. Consistent with these observations, immunohistochemical analysis demonstrated ICAM-2 expression in primary neuroblastoma tumors exhibiting features that are associated with limited metastatic disease and more favorable clinical outcome. In neuroblastoma cell lines, ICAM-2 expression did not affect AKT activation, tumorigenic potential or chemosensitivity, as has been reported for some types of transfected cells. The observed ICAM-2-mediated suppression of metastatic phenotype is a novel function for this protein, and the interaction of ICAM-2/α-actinin/actin represents the first complete membrane-linker protein-actin linkage to impact tumor cell motility in vitro and metastatic potential in an in vivo model. Current work focuses on identifying specific protein domains critical to the regulation of neuroblastoma cell motility and metastasis and on determining if these domains represent exploitable therapeutic targets

Development of a Tumor-Selective Approach to Treat Metastatic Cancer

BACKGROUND: Patients diagnosed with metastatic cancer have almost uniformly poor prognoses. The treatments available for patients with disseminated disease are usually not curative and have side effects that limit the therapy that can be given. A treatment that is selectively toxic to tumors would maximize the beneficial effects of therapy and minimize side effects, potentially enabling effective treatment to be administered. METHODS AND FINDINGS: We postulated that the tumor-tropic property of stem cells or progenitor cells could be exploited to selectively deliver a therapeutic gene to metastatic solid tumors, and that expression of an appropriate transgene at tumor loci might mediate cures of metastatic disease. To test this hypothesis, we injected HB1.F3.C1 cells transduced to express an enzyme that efficiently activates the anti-cancer prodrug CPT-11 intravenously into mice bearing disseminated neuroblastoma tumors. The HB1.F3.C1 cells migrated selectively to tumor sites regardless of the size or anatomical location of the tumors. Mice were then treated systemically with CPT-11, and the efficacy of treatment was monitored. Mice treated with the combination of HB1.F3.C1 cells expressing the CPT-11-activating enzyme and this prodrug produced tumor-free survival of 100% of the mice for >6 months (P<0.001 compared to control groups). CONCLUSIONS: The novel and significant finding of this study is that it may be possible to exploit the tumor-tropic property of stem or progenitor cells to mediate effective, tumor-selective therapy for metastatic tumors, for which no tolerated curative treatments are currently available

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Nucleoside transport in normal and neoplastic cells

The permeation of nucleosides across the plasma membrane of mammalian cells is complex and mediated by at least five distinct transporters that differ in their sensitivity to inhibitors and in their specificity for nucleosides. The basic properties and permeant specificity of these transporters are summarized in Table 3. It appears that there may be differences in the distribution of these transporters in tumors and normal tissues that might be exploited for chemotherapeutic purposes. The human tumor cell lines examined express predominantly the NBMPR-sensitive equilibrative transporter es which can be blocked by low concentrations of NBMPR and dipyridamole. It is reasonable to expect that tumors with transport properties similar to the CCRF-CEM and Rh28 cell lines (Table 1) that have no detectable NBMPR-insensitive transport activity will be highly susceptible to the therapeutic approach of combining a transport inhibitor such as dipyridamole or NBMPR with an inhibitor of de novo pyrimidine biosynthesis. On the other hand, this approach to therapy is unlikely to succeed against tumors with transport phenotypes similar to the WI-L2 cell line that may permit the salvage nucleosides in the presence of these inhibitors. The majority of tumor cells examined, however, fall between these extremes, and it is not yet known what level of NBMPR-insensitive transport activity can be tolerated without seriously compromising this therapeutic approach. With respect to normal tissues, the mature absorptive cells of the intestine have predominantly Na+-dependent nucleoside transporters that are insensitive to NBMPR and dipyridamole. The proliferating crypt cells also appear to have Na+-dependent nucleoside transport, although they may also have an NBMPR-sensitive component of transport (Belt, unpublished data). Bone marrow granulocyte-macrophage progenitor cells also appear to have one or more concentrative nucleoside transporters. Thus these tissues, which are most vulnerable to the toxicity of antimetabolites, may be able to salvage nucleosides in the presence of inhibitors of equilibrative transport and be protected from the toxicity of de novo synthesis inhibitors. It is likely, however, that a successful application of this therapeutic approach will require the analysis of the nucleoside transport phenotype of individual tumors in order to identify those patients that may benefit from such therapy. Since the development of antibodies (66-68) and cDNA probes (69, 70) for the various nucleoside transporters is currently underway in several laboratories, it is likely that analysis of the nucleoside transport phenotype of tumors from biopsy material will be feasible in the future. © 1993