Antigen receptor signaling to NF-?B is a highly regulated, critical pathway for B and T lymphocyte activation during the adaptive immune response. NF-?B controls many genes required for lymphocyte function including genes that promote proliferation and survival. The inappropriate activation of NF-?B is associated with multiple leukemias and lymphomas, which frequently acquire mutations in signaling molecules that elicit their receptor- independent constitutive NF-?B activity. CARD11 (CARMA1) is a key scaffold protein that functions in both T cell receptor and B cell receptor pathways to transmit signals from the engaged receptor to the activation of the IKK complex and NF-?B. Aberrant CARD11-dependent signaling is required for the dysregulated proliferation of the activated B cell-like (ABC) subtype of Diffuse Large B Cell Lymphoma (DLBCL), and mutations in CARD11, which hyperactivate the protein, are found in ~10% of patient samples of ABC DLBCL. Previous work has established that during normal signaling, CARD11 undergoes a transition from an inactive to an active signaling scaffold that recruits several signaling cofactors into a complex that induces IKK activity. An Inhibitory Domain (ID) in CARD11 controls this transition;it keeps CARD11 inactive in the basal state, but receives signals from the engaged receptor that neutralize its inhibitory action and allow CARD11 to signal. However, it remains poorly understood how activated CARD11 signals to NF-?B, how precisely the ID functions, how lymphoma-associated mutations hyperactivate CARD11, and how aberrant CARD11 signaling causes disease. In this application, we will 1) characterize a novel collection of gain-of-function and loss-of- function CARD11 variants to define critical mechanisms of normal and oncogenic CARD11 signaling;2) determine the mechanistic basis for how the Inhibitory Domain of CARD11 governs signal-dependent CARD11 activation;3) test the hypothesis that hyperactive CARD11 is sufficient to alter B cell development and promote unwarranted B cell proliferation;and 4) characterize novel CARD11 signaling cofactors that we have recently identified. Our studies will help illuminate how signaling proteins, especially scaffolds, employ autoinhibitory mechanisms to allow their signal-induced activation, and how cancers exploit these mechanisms by selecting for mutations that bypass regulation to promote proliferation and survival. In addition, our results are likely to provide a catalogue of mutations that could underle the development of lymphomas in humans and therefore offer novel diagnostic insight and opportunities. Finally, our studies should reveal previously unrecognized molecular targets for the development of new therapies designed to treat NF-?B-dependent cancers and other diseases that result from aberrant immune cell behavior.
The normal function of the immune system depends on the ability of white blood cells, or lymphocytes, to detect foreign pathogens and respond appropriately so that a pathogen is eliminated without damage to the host. This proposal is designed to expand understanding of the molecular machinery that is used by lymphocytes in this process, and uncover how the mutation or dysregulation of this machinery leads to the inappropriate growth of cancers of immune cells, including lymphomas. Our results are likely to provide a catalogue of mutations that could underlie the development of lymphomas in humans and therefore offer novel diagnostic insight and opportunities. In addition, our studies may reveal molecular targets for the development of new therapies designed to treat these cancers and other diseases that result from aberrant immune cell behavior.