Kanki, John

We are studying cancer genetics using the zebrafish animal model, in combination with murine and cell culture systems, to dissect developmental pathways subverted in human leukemias and solid tumors. The zebrafish model is an established system for studying vertebrate embryogenesis, organogenesis and disease. A powerful attribute of the zebrafish is its capacity for performing large-scale forward genetic screens on transparent, readily accessible embryos. Thus, the zebrafish is an ideal system for identifying novel genes involved in cancer, as their discovery is based on unbiased phenotypic assays and can uncover genes that are either activated (oncogenes) or inactivated (tumor suppressors) during malignant transformation. Using genome-wide mutagenesis screening strategies and TILLING in conjunction with transgenic approaches we are generating zebrafish models of several different cancers.

Zebrafish myelopoiesis is very similar to that in humans and we postulate that through our mutagenesis screens we will identify a subset of genes that both regulates normal myelopoiesis and contributes to the pathogenesis of two important human diseases - myelodysplastic syndrome and acute myeloid leukemia. A second screen is underway to uncover genes disrupted in neuroblastoma, the most common extra-cranial solid tumor of children. These embryonic tumors arise in the peripheral sympathetic nervous system (PSNS) and most of the genes regulating both PSNS development and neuroblastoma formation have yet to be identified. Through these screens we have identified new genes required for normal myelopoiesis and PSNS development and are currently studying their respective contributions to neoplastic pathogenesis. Cell death mechanisms also contribute to malignant transformation and p53, a critical regulator of DNA repair and apoptosis, is the most commonly mutated gene among all cancers. We have recently isolated a mutant p53 zebrafish line that is tumor-prone and is currently being used in conjunction with our zebrafish cancer models to determine how p53 contributes to tissue-specific tumors.

We have shown that human T-cell leukemias can be divided into five major subtypes based on the expression of oncogenes that initiate malignant transformation, and in addition, have generated transgenic zebrafish lines overexpressing Myc that develop leukemia, recapitulating one of these human T-ALL subtypes. We are now conducting one of the first “cancer-related” modifier screens in a vertebrate system to identify both enhancers and suppressors of T-cell leukemia. Chemical and genetic modifier screens using tumor-prone zebrafish lines may ultimately reveal mutant genes or drugs that can suppress or modify disease progression. We hope to identify such modifiers that can either promote specific aspects of the malignancy, such as genomic instability or metastasis, or that delays/suppresses tumor onset. We are also utilizing innovative in vitro genome-scale location analysis (GSLA), combining chromatin immunoprecipitation with hybridization to human promoter microarrays to identify the direct targets of prevalent oncogenic transcription factors. We are validating the significance of key subsets of candidate targets through siRNA strategies and assessing whether their functional inhibition retards aberrant cell growth and survival in panels of cell lines derived from human cancers. Through the combination of these approaches we hope to uncover novel genes and targets for the development of small molecule inhibitors and new cancer therapies.