2670

GFAP

-;glial fibrillary acidic protein;GFAP;glial fibrillary acidic protein

-

17q21

protein-coding

Retinoblastoma, the most common intraocular tumor of childhood, is a malignant neoplasm that arises during retinal development. The embryonal cell target for neoplastic transformation is not yet clearly defined. To better understand the histogenetic potential of this tumor, the expression of photoreceptor and glial cell-associated proteins were examined in 22 primary retinoblastomas. Interphotoreceptor retinol-binding protein (IRBP), cone and rod opsins were selected as the photoreceptor specific proteins due to their different temporal patterns of expression during normal retinal development. Neoplastic Muller celldifferentiation, and non-neoplastic reactive astrocytes were identified using cellular retinaldehyde binding-protein (CRAlBP), and glial fibrillary acidic protein (GFAP), respectively. Photoreceptor proteins were present in 16 cases and showed different cellular patterns of expression. IRBP and cone opsin were usually abundant. Although rod opsin was clearly identified in eight tumors, itsexpression was more restricted than either IRBP or cone opsin. This differentialpattern of expression, opposite to the normal pattern of photoreceptor gene expression in the adult retina, corresponded to a marked decrease in mRNA for rod opsin. Cone opsin and IRBP colocalized in fleurettes demonstrating that neoplastic human cone cells are capable of IRBP synthesis. Muller cell differentiation was present in 12 of the 16 cases in which photoreceptor proteins were detected. In contrast, GFAP was only present in reactive, stromal astrocytes associated with blood vessels. Our data suggest that the retinoblastoma has the histogenetic potential of the immature neural retinal epithelium which can give rise to both photoreceptor and Muller cell lineages. The differential expressionof cone and rod phenotypes in retinoblastoma is consistent with the "default" mechanism of cone cell differentiation.

The most common microdeletion in humans involves the 22q11 region. Congenital anomalies associated with 22q11 loss include cardiac and facial defects. Less frequent is the co-presentation of malignant rhabdoid tumors that are highly aggressive childhood malignancies typically found in renal or extra-renal soft tissues and central nervous system. A newborn patient presented with multiple congenital anomalies consistent with 22q11 deletion syndrome including cleft lipand palate, ear tags and ventricular septal defects co-presenting with an axillary rhabdoid tumor. Comparative genomic hybridization revealed a 2.8 Mb germline deletion in the 22q11.2 region containing genes required for normal fetal development and the SMARCB1 tumor suppressor gene. Analysis of tumor DNA revealed a somatic deletion of exon 7 in the second allele of SMARCB1. expression of SMARCB1 was absent, while tumor markers including MYC, GFAP, and CLAUDIN-6 were upregulated. The presence of tandem oriented BCRL modules located within interspersed low copy repeat elements throughout the 22q11 distal region may predispose this area for microdeletions through nonalleleic homologous recombination.#CI- Copyright (c) 2011 Wiley-Liss, Inc.

Medulloblastomas are the most common malignant brain tumors in childhood. Emerging evidence suggests that medulloblastoma comprises at least four distinctdiseases (WNT, SHH, Group 3 and 4) with different biology, clinical presentation, and outcome, with especially poor prognosis in Group 3. The tight connection of biology and clinical behavior in patients emphasizes the need for subgroup-specific preclinical models in order to develop treatments tailored to each subgroup. Herein we report on the novel cell line HD-MB03, isolated from tumor material of a patient with metastasized Group 3 medulloblastoma, and preclinical testing of different histone deacetylase inhibitors (HDACis) in thismodel. HD-MB03 cells grow long term in vitro and form metastatic tumors in vivo upon orthotopic transplantation. HD-MB03 cells reflect the original Group 3 medulloblastoma at the histological and molecular level, showing large cell morphology, similar expression patterns for markers Ki67, p53, and glial fibrillary acidic protein (GFAP), a gene expression profile most closely matching Group 3 medulloblastomas, and persistence of typical molecular alterations, i.e., isochromosome 17q [i(17q)] and MYC amplification. Protein expression analysis ofHDACs 2, 5, 8, and 9 as well as the predictive marker HR23B showed intermediate to strong expression, suggesting sensitivity to HDACis. Indeed, treatment with HDACis Helminthosporium carbonum (HC)-toxin, vorinostat, and panobinostat revealed high sensitivity to this novel drug class, as well as a radiation-sensitizing effect with significantly increased cell death upon concomitant treatment. In summary, our data indicate that HD-MB03 is a suitable preclinical model for Group 3 medulloblastoma, and HDACis could represent a therapeutic option for this subgroup.