Proviral Tagging Combined with Human Microarray Data Reveals Genes and Pathways That Cooperate in Disease Induction.

Retroviruses induce hematopoietic cancer by integrating into the genome and insertionally mutating cancer causing genes and provide powerful molecular tags for cancer gene identification. Retroviruses induce cancer following several rounds of insertional mutagenesis and clonal selection; as a result, each tumor contains multiple retroviral integrations that mark the location of cooperating cancer genes. Some retroviral integrations occur early in tumor formation and initiate tumorigenesis while others occur late and promote tumor progression. Using ligation-mediated PCR (LM-PCR), a new technique that permits the automated cloning and sequencing of thousands of retroviral integration sites per day, we are now able to rapidly identify the many initiation and progression events that cooperate to produce a mouse tumor. We have used LM-PCR to identify the myriad of genes that cooperate with activating mutations at [itallic]Lmo2 in leukemia induction. We compare our mouse results with the published microarray data for 19 human tumors that overexpress LMO2 and demonstrate a remarkable correlation between the genes causally associated with murine Lmo2 leukemias and the genes overexpressed in human LMO2 leukemias. Our studies highlight the power of LM-PCR for sampling tumor microheterogeneity and provide a powerful new means for interpreting and annotating human microarray data.