Introduction: Choroid plexus tumors are rare intraventricular papillary neoplasms of the choroid plexus (CP) epithelium. They occur most often in childhood and comprise 10-20% of all brain tumors in infants. Choroid plexus papilloma is a benign tumor, whereas choroid plexus carcinoma is malignant and most commonly found in pediatric population. Despite good prognosis for choroid plexus papilloma after complete surgical removal, partially resected or inaccessible tumors, and choroid plexus carcinomas are often associated with poor outcomes. Multiple factors including Notch signaling have been implicated in CP tumor development, however, the cell of origin and mechanisms of CP tumor formation remain unclear. In this study, we developed a genetic model of CP tumor induced by Notch pathway activation. Our studies indicate Notch-induced CP tumor is closely related to CP development and is driven by Sonic Hedgehog (Shh) signaling pathway.
Methods: Math1-Cre transgenic strain was bred with Rosa26-NICD1 strain that express Notch 1 intracellular domain (NICD1) in a Cre-dependent manner. Math1-Cre/Rosa26-NICD1 animals were further crossed to green fluorescent protein (GFP) Cre reporter (Rosa26-GFP) strain to label Math1-positive lineage from rhombic lip. Transgene expression was analyzed by immunostaining for GFP co-expressed with NICD1 from the Rosa26 locus. Tumor cell proliferation was measured by immunostaining for Ki67 and EdU incorporation assay. Cell differentiation and survival were determined by immunohistochemistry analysis of lineage markers expression and cleaved caspase 3 staining respectively. Gene expression was examined by quantitative RT-PCR analysis and immunostaining.
Results: Math1-postive rhombic lip lineage was detected in a small fraction of choroid plexus epithelium of 4th ventricle. The choroid plexus cells derived from Math1+ neural progenitors expressed Lmx1a, Otx2, early markers for CP epithelial lineage, and Aquaporin 1 (AQP1), marker for differentiated CP epithelial cells. In Math1-Cre/Rosa26-NICD1 animals, an abnormal growth was observed in hindbrain CP derived from Math1-positive rhombic lip neural progenitors. EdU incorporation assay and Ki67 staining revealed papillary and intraventricular growth of epithelial cells that exhibited enhanced proliferation compared to control animals in early postnatal period. Though tumor cells expressed Lmx1a, Otx2, they didn't express AQP1 and MafB, marker for CP mesenchyme. Quantitative RT-PCR analysis revealed that the expression of transthyretin (Ttr), a CP epithelial marker, was reduced in CP tumor cells, while the expression levels of Notch pathway target genes, Hes1 and Hes5, were increased in tumor cells. Proliferating CP tumor cells exhibited higher levels of expression for Gli1, MycN, effectors of the Shh signaling, indicating aberrant activation of Shh pathway.
Conclusions: Math1-positive rhombic lip lineage contributes to CP epithelium and is sensitive to Notch 1-induced tumor formation. We have developed a genetic model of CP tumor that exhibits characteristics of pediatric CP tumors. Notch 1-induced CP tumor cells have properties of CP progenitors and lack terminal differentiation. These CP tumors exhibit a transient enhanced proliferation synchronous with enhanced activity of the Shh pathway. Animal models of CP tumors have great potential to facilitate the discovery and development molecular diagnostics and targeted therapies for these rare pediatric malignancies.
Citation Format: Li Li, Katie Picotte, Brian Westerhuis, Haotian Zhao. Notch 1 signaling-induced choroid plexus tumor arises from epithelial progenitor via Sonic Hedgehog pathway. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr B3.