Genetic determinants promoting resistance to bcr-loss in b-cell lymphomas
Loss of B-Cell Receptor (BCR) in lymphoma B cells leads to attenuated PI3K/AKT signaling and altered Myc-dependent transcriptional output, resulting in a competitive disadvantage in BCR-deficient lymphoma cells. The acquisition of genetic events restoring signaling competence is sufficient to improve cellular fitness in BCR-deficient lymphomas. A fraction of Non-Hodgkin-B-cell lymphomas carry missense mutations in FOXO1, a transcription factor essential during B cell development, and a main target of the PI3K/AKT pathway, which relays survival signals downstream of the BCR. In preliminary studies, we found that cells with FOXO1 mutations rewire their signaling status showing a) activation of stress-activated protein kinases (SAPKs) and PI3K/AKT, b) altered responses to key upstream receptors, such as CD40 and BCR, and c) improved fitness. In this context, I propose to investigate whether FOXO1 mutations are able to provide resistance to BCR-loss in transformed B cells, by favoring the activation of PI3K/AKT, SAPK/JNK (and potentially other) signaling pathways. This hypothesis will be tested using mouse and human models that allow conditional deletion of the BCR in FOXO1 mutant B cells, determining whether expression of FOXO1 mutations is: a) sufficient to release normal B cells from BCR-dependency, and b) able to restore competitive fitness to BCR-deficient lymphomas.  Moreover, combining CRISPR/Cas9 and chemical screenings, I propose to identify novel factors sustaining the growth of lymphoma cells that lost BCR expression. Overall, this research proposal will address relevant, yet unanswered questions in the biology of B cell lymphomas, providing a better understanding into the complexity of signaling competence in normal and transformed B cells, and identifying novel factors promoting independence from BCR signaling, to be exploited as therapeutic targets for the treatment of B cell lymphomas resistant to BCR-specific inhibitors.