RESUMEN
Neuroendocrine tumors (NETs), which can have survival rates as low as 4%, currently have limited therapeutic interventions available highlighting the dire need for the identification of novel biological targets for use as new potential drug targets. One such potential target is retinoblastoma-binding protein 2 (RBP2), an H3K4 demethylase whose overexpression has been linked to cancer formation and metastasis in non-endocrine tumor types. We measured RBP2 mRNA and protein levels in enteropancreatic NETs by measuring RBP2 in matched human normal and NET tissue samples. Further, proliferation, migration, invasion and colony formation assays were performed in the physiologically relevant NET cell lines ßlox5, H727 and QGP-1 to understand the role of RBP2 and its demethylase activity on end points of tumorigenesis. Our data indicate a strong correlation between RBP2 mRNA and protein expression in NET specimens. RBP2 was overexpressed relative to tissue-matched normal controls in 80% of the human tumors measured. In vitro studies showed RBP2 overexpression significantly increased proliferation, migration, invasion and colony formation, whereas knockdown significantly decreases the same parameters in a demethylase-independent manner. The cell cycle inhibitors p21 and p57 decreased with RBP2 overexpression and increased upon its depletion, suggesting a regulatory role for RBP2 in cellular proliferation. Taken together, our results support the hypothesis that the aberrant overexpression of RBP2 is a frequent contributing factor to tumor formation and metastasis in enteropancreatic NETs.
RESUMEN
Rhabdomyosarcoma, one of the most common childhood sarcomas, is comprised of two main subtypes, embryonal and alveolar (ARMS). ARMS, the more aggressive subtype, is primarily characterized by the t(2;13)(p35;p14) chromosomal translocation, which fuses two transcription factors, PAX3 and FOXO1 to generate the oncogenic fusion protein PAX3-FOXO1. Patients with PAX3-FOXO1-postitive tumors have a poor prognosis, in part due to the enhanced local invasive capacity of these cells, which leads to the increased metastatic potential for this tumor. Despite this knowledge, little is known about the role that the oncogenic fusion protein has in this increased invasive potential. In this report we use large-scale comparative transcriptomic analyses in physiologically relevant primary myoblasts to demonstrate that the presence of PAX3-FOXO1 is sufficient to alter the expression of 70 mRNA and 27 miRNA in a manner predicted to promote cellular invasion. In contrast the expression of PAX3 alters 60 mRNA and 23 miRNA in a manner predicted to inhibit invasion. We demonstrate that these alterations in mRNA and miRNA translate into changes in the invasive potential of primary myoblasts with PAX3-FOXO1 increasing invasion nearly 2-fold while PAX3 decreases invasion nearly 4-fold. Taken together, these results allow us to build off of previous reports and develop a more expansive molecular model by which the presence of PAX3-FOXO1 alters global gene regulatory networks to enhance the local invasiveness of cells. Further, the global nature of our observed changes highlights the fact that instead of focusing on a single-gene target, we must develop multi-faceted treatment regimens targeting multiple genes of a single oncogenic phenotype or multiple genes that target different oncogenic phenotypes for tumor progression.