Identification of oncogenes in human B-cell and murine T-cell lymphomas

Abstract

The development of cancer is a multi-step event that involves a series of genetic changes to disrupt the normal processes of the cell. My thesis research was to identify genes that are involved in human, B-cell, non-Hodgkin's lymphomas (NHLs) and in murine retrovirus induced T-cell lymphomas.;We analyzed five independent B-cell NHLs containing chromosomal rearrangements involving band 12q13. FISH was used to map the breakpoints more precisely where two were within 1 Mb of each other. BAC clones were used to generate a high resolution physical map of 12q13 where the contig was submitted to the Baylor College of Medicine and the draft sequence obtained as part of the human genome project. Although the breakpoints in the two tumors were very close to each other, they involved distinct genes. Therefore, for the remainder of this thesis project, I utilized a different approach to identifying oncogenes that are activated in lymphomas.;Insertional mutagenesis by retroviruses provides a powerful tool to identify new genes that cause cancer. The murine retrovirus SL3-3 (SL3) induces T-cell lymphomas. Like most other oncogenic retroviruses, SL3 activates the expression of cellular oncogenes by proviral insertion. Identification of the same proviral target in multiple independent tumors (common integration sites), provides compelling genetic evidence that gene functions as an oncogene. 48 tumors were put through inverse PCR to amplify 128 junction fragments from SL3-induced tumors. Novel loci that were hit by more than one provirus in independent tumors were designated as common SL3 integration (Si) sites. Twenty Si sites were identified where the flanking genes were identified by searches of GenBank, public mouse genome databases and genetic mapping with a mouse interspecific backcross panel.;The gene that was the most frequently utilized site by SL3, with insertions in 20% of the tumors, was Rras2. Insertions as far as 57 kb away from the transcribed portion were associated with substantially increased transcription of Rras2, and no coding sequence mutations including those typically involved in Ras activation were detected. The genetic evidence presented here that unmutated Rras2 is frequently activated by proviral insertion in tumors provides strong support for the hypothesis that inappropriate expression of normal Rras2 protein might contribute to human cancer.