The role of microRNAs in paediatric malignant germ cell tumours (MGCTs) and germ cell development

Aims: To investigate the role of tiny genetic regulators (microRNAs) in childhood malignant germ cell tumours (MGCTs) to improve management of such cancers.

Research Proposal: MGCTs come from egg- or sperm-producing cells, representing 4% of childhood cancers. They occur in testes/ovaries (gonadal) and other body sites (extragonadal). There are different types, depending on tumour cell appearance under the microscope, although all are treated identically. Compared with other paediatric tumours, very little is known regarding factors that affect outcome in MGCTs. Studies of genetic changes in tumours may give an indication of the likely response to treatment. We have analysed expression of tiny fragments of genetic code called microRNA in MGCT samples. MicroRNAs act as cancer-forming genes by regulating other genetic code (messenger RNA) which produce proteins that control cell growth/vital functions.

Prospective outcomes: Include identification of common/distinct patterns of microRNA expression between different MGCTs; correlation of these profiles with other MGCT genetic changes and clinical features; comparison with microRNA profiles in adult MGCTs; studying effects of altering microRNA levels in model systems.

Expected benefits: Our findings may allow identification of 'biomarkers' used to help diagnosis and predict outcome in MGCTs as well as suggesting potential targets for new drug treatments.

Aims/objectives: By studying the role of microRNAs in paediatric malignant germ cell tumours (MGCTs) and germ cell development we aim to 1) identify diagnostic tools/prognostic markers 2) suggest targets for the generation of novel therapeutic agents and 3) identify microRNAs that play an important role in vertebrate development.

Background: Paediatric MGCTs occur at several different anatomical sites and are heterogeneous in nature. There are a number of different histological subtypes, but despite this, treatment is almost identical for all cases. They represent 4% of cancers in childhood, but their incidence is increasing and, furthermore, testicular MGCTs are a leading cause of death in young men. Our understanding of MGCT biology lags significantly behind other paediatric solid tumours and leukaemias. MicroRNAs (miRNAs) are short, non protein-coding RNAs that act post-transcriptionally as regulators of gene expression. miRNAs act as oncogenes and tumour suppressor genes in their own right and are reported to be diagnostic and prognostic markers in certain cancers. We propose to study these novel gene regulators in this under-investigated paediatric cancer group.

Design/methodology: Using Exiqon microarray technology we have performed global expression profiling for 585 known human miRNAs, using the UK national collection of paediatric MGCTs as well as control tissues and cell lines. Unsupervised analysis, determined by the expression of 275 miRNAs, demonstrated clustering largely by histological subtype. Supervised clustering analysis identified 127 known miRNAs most differentially expressed between histological subtypes, controls and cell lines (p<0.0001). Current validation of this data using Taqman quantitative real time PCR (qRT-PCR) and in-situ hybridisation (ISH) is in progress. We will further investigate common/distinct patterns of miRNA expression between different subtypes of MGCT and between adult and childhood disease, exploiting the extensive clinical and follow-up data that is available. We will relate these profiles to genomic changes and protein-coding gene expression profiles in the same samples. We will independently validate our findings on separate MGCT samples/tissue microarray. Using bioinformatics (e.g. miRBase) we will identify candidate miRNAs that act as oncogenes or tumour suppressor genes via direct negative regulation of protein-coding genes involved in the pathogenesis of MGCTs.

Scientific opportunities will arise from functional studies looking at the biological effects of over-expression/depletion of these miRNAs in MGCT cell lines. Collaboration on a Xenopus model will allow study of microRNA expression during vertebrate development.

Medical opportunities will arise from identification of key miRNAs that can be used diagnostically and prognostically as clinical tools.