CSIG-24. TARGETED INHIBITION OF CDK5-MEDIATED REGULATION OF HUMAN ENDOGENOUS RETROVIRUS K (HML-2) ENVELOPE PROTEIN IN ATYPICAL TERATOID RHABDOID TUMOR

Atypical teratoid rhabdoid tumor (ATRT) is a pediatric brain tumor with a high mortality rate characterized by mutations in/ deletions of SWI/SNF matrix-associated actin-dependent regulator of chromatin sub-family B member 1 (SMARCB1). We previously showed that loss of SMARCB1 causes up-regulation and release of HML-2 subfamily of human endogenous retrovirus K envelope protein (HML-2 ENV), resulting in maintenance of pluripotency. Here, we investigated intracellular trafficking and release of HML-2 ENV. Further, we demonstrate two potential therapeutic strategies to decrease intracellular HML-2 ENV: 1) inhibition of calcium influx by ouabain, a cardiac glycoside toxic to neural stem cells, and 2) targeted inhibition of cyclin-dependent kinase 5 (CDK5), which is restricted to neurons by p35, its activator protein, by TP5. ATRT cell lines and tumor tissue obtained from patients were confirmed for SMARCB1 loss and increased HML-2 ENV. Cell viability and intracellular HML-2 ENV concentration were measured after treatment with ouabain and TP5 (CDK5 antagonist). We evaluated the calcium-mediated effect of ouabain on HML-2 intracellular concentration by treating the cells with ouabain, the calcium chelators calcimycin and EGTA, and calpeptin, a calpain inhibitor, which activates CDK5, and measuring HML-2 ENV and p35. We evaluated HML-2 ENV for a CDK5 consensus phosphorylation site and performed co-immunoprecipitation to evaluate direct interaction. We evaluated activity of CDK5 in ATRT cell lines by autoradiography. Both Ouabain and TP5 caused a decrease in cell viability in a dose-dependent manner. Further, ouabain treatment decreased HML-2 ENV intracellular concentration. We found that HML-2 ENV contains a consensus phosphorylation site for CDK5. We discovered that HML-2 ENV was bound to CDK5. We established that ATRT cell lines had hyperactive CDK5. Finally, we established that the effect of ouabain on HML-2 ENV was due to indirect inhibition of calcium-mediated activation of calpain and thus CDK5.

The Identification of MiRNA and MRNA Expression Profiles Associated with Pediatric Atypical Teratoid/rhabdoid Tumor

Background: Atypical teratoid/rhabdoid tumor (AT/RT) is a malignant pediatric tumor of the central nervous system (CNS) with high recurrence and low survival rates that is often misdiagnosed. MicroRNAs (miRNAs) are involved in the tumorigenesis of numerous pediatric cancers, but their roles in AT/RT remain unclear.Methods: In this study, we used miRNA sequencing and gene expression microarrays from patient tissue to study both the miRNAome and transcriptome traits of AT/RT.Results: Our findings demonstrate that 5 miRNAs were up-regulated, 16 miRNAs were down-regulated, 179 mRNAs were up-regulated and 402 mRNAs were down-regulated in AT/RT. The expressions of hsa-miR-17-5p and MAP7 mRNA showed the most significant differences in AT/RT tissues as assayed by qPCR, and analyses using the miRTarBase database identified MAP7 mRNA as a target gene of hsa-miR-17-5p. Conclusions: Our findings suggest that the dysregulation of hsa-miR-17-5p may be a pivotal event in AT/RT and MAP7 miRNAs that may represent potential therapeutic targets and diagnostic biomarkers.