Cell Dynamics Group
Frequency and duration of intracellular signaling are associated with distinct biological responses. A major focus of the Cell Dynamics Group is to understand how dynamic control of Ca2+ and PI3K signaling determine negative B-cell selection. We are using optogenetic approaches to examine the mechanisms by which B cells can interpret differences in: (i) frequency of Ca2+ oscillations; and (ii) duration of PI3K activation.
(ii) Central tolerance mechanisms sense pathological B cells based on abnormal signaling patterns
Normal antigen encounter of B cells results in a short transient PI3K signal, which is distinct from persistent activation of PI3K signaling in the context of pathological BCR signaling (autoreactive BCR or transforming oncogene). We test the hypothesis that central tolerance mechanisms sense and eliminate (pre-) malignant B-cells based on protracted activation of the PI3K pathway.
In collaboration with Derek Toomre (Yale), we engineered human B-ALL and mantle cell lymphoma (MCL) cells with Opto-PI3K consisting of the light-responsive Arabidopsis thaliana transcription factor CIB1 and cryptochrome 2 (CRY2) fused to the inner SH2 (iSH2) region of the p85α regulatory subunit of PI3K (Idevall-Hagren et al., 2012). Exposure to blue light pulse induces a conformational change of CRY2 and its interaction with the membrane anchored N-terminus of CIB1 (CIBN). This interaction results in membrane-recruitment of the CRY2-iSH2 that binds the endogenous p110α catalytic subunit of PI3K, and eventually transient PI3K-activation (Figure 3).