In this grant the major goal is to investigate mechanisms regulating quiescent B cells either poised in the GO stage of the cell cycle (GO B cells) or leaving GO to enter the cell cycle. We have found that caspases- a family of cysteine proteases involved in programmed death of B cells- also regulates B cell entry into the cell cycle. The caspase-6 inhibitor VEID blocks proliferation of GO B cells. However, caspase inhibitors do not block induction of inhibitors of apoptosis (lAPs). Our data suggest caspases are required for a pathway common to all modes of inducing B cells into the cell cycle.
Our Aims are:
Aim 1 : To define the requirements for caspase activation in B cells, i.e., the signaling pathways upstream of caspase activation in B cells. We will test whether or not different receptors activate the same or distinct sets of caspases in GO B cells. We will test the hypothesis that T cell dependent (TD) vs. T cell independent (TI) signaling receptors activate similar or distinct caspase pathways in GO B cells. We will define the upstream pathways required for activating caspase-6 and -8 in B cells. Using a dominant negative (DN) form of FADD or caspase-6 and B cells from caspase-6 knockout mice, we will test if activation of caspase-6 is required for activation of caspase-8 or vice versa. We will also test if clAPs, when activated via CD40, contribute to the selective activation of caspases -6 and -8 and ceil cycle entry.
Aim 2. We will test the hypothesis that caspase-6 cleaves a functional set of substrates in GO B cells as they enter the cell cycle and activate a survival program. First, we will characterize the cell cycle block observed upon inhibition of caspase-6. Second, we will define substrates for caspase-6 and assess their roles in B cells. We will define where caspase-6 goes in B cells after they are activated and how the caspase-6 substrate, SATB1, is regulated by caspase-6 in B cells.
Aim 3. We will characterize the B cell defects in caspase-6 -/- mice and compare the survival of B cell subsets in wildtype vs. CD40 -/- or caspase-6 -/- mice. We predict that caspase-6 and CD40 are required for optimal B cell survival. We will also test if caspases selectively regulate homeostasis and expansion of B cell subsets. These studies will provide new insights into the mechanisms, which regulate the survival of normal B cells, malignant B cells and B cells contributing to autoimmune diseases
| Richards, Sabrina M; Clark, Edward A (2009) BCR-induced superoxide negatively regulates B-cell proliferation and T-cell-independent type 2 Ab responses. Eur J Immunol 39:3395-403 |
| Ma, Daphne Y; Clark, Edward A (2009) The role of CD40 and CD154/CD40L in dendritic cells. Semin Immunol 21:265-72 |
| Watanabe, Chie; Shu, Geraldine L; Zheng, Timothy S et al. (2008) Caspase 6 regulates B cell activation and differentiation into plasma cells. J Immunol 181:6810-9 |
| Richards, Sabrina; Watanabe, Chie; Santos, Lorna et al. (2008) Regulation of B-cell entry into the cell cycle. Immunol Rev 224:183-200 |
| Craxton, Andrew; Draves, Kevin E; Clark, Edward A (2007) Bim regulates BCR-induced entry of B cells into the cell cycle. Eur J Immunol 37:2715-22 |
| Acosta-Rodriguez, Eva V; Craxton, Andrew; Hendricks, Deborah W et al. (2007) BAFF and LPS cooperate to induce B cells to become susceptible to CD95/Fas-mediated cell death. Eur J Immunol 37:990-1000 |
| Paterson, Jennifer C; Tedoldi, Sara; Craxton, Andrew et al. (2006) The differential expression of LCK and BAFF-receptor and their role in apoptosis in human lymphomas. Haematologica 91:772-80 |
| Graves, Jonathan D; Craxton, Andrew; Clark, Edward A (2004) Modulation and function of caspase pathways in B lymphocytes. Immunol Rev 197:129-46 |
| Craxton, Andrew; Magaletti, Dario; Ryan, Elizabeth J et al. (2003) Macrophage- and dendritic cell--dependent regulation of human B-cell proliferation requires the TNF family ligand BAFF. Blood 101:4464-71 |
| Olson, N Eric; Graves, Jonathan D; Shu, Geraldine L et al. (2003) Caspase activity is required for stimulated B lymphocytes to enter the cell cycle. J Immunol 170:6065-72 |
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