The caspase recruitment domain family member 11 (CARD11 or CARMA1)—B cell CLL/lymphoma 10 (BCL10)—MALT1 paracaspase (MALT1) [CBM] signalosome complex serves as a molecular bridge between cell surface antigen receptor signaling and the activation of the NF-κB, JNK, and mTORC1 signaling axes. This positions the CBM complex as a critical regulator of lymphocyte activation, proliferation, survival, and metabolism. Inborn errors in each of the CBM components have now been linked to a diverse group of human primary immunodeficiency diseases termed “CBM-opathies.” Clinical manifestations range from severe combined immunodeficiency to selective B cell lymphocytosis, atopic disease, and specific humoral defects. This surprisingly broad spectrum of phenotypes underscores the importance of “tuning” CBM signaling to preserve immune homeostasis. Here, we review the distinct clinical and immunological phenotypes associated with human CBM complex mutations and introduce new avenues for targeted therapeutic intervention.

Lyn kinase functions as a regulator of imatinib sensitivity in chronic myelogenous leukemia (CML) cells through an unknown mechanism. In patients who fail imatinib therapy but have no detectable BCR-ABL kinase mutation, we detected persistently activated Lyn kinase. In imatinib-resistant CML cells and patients, Lyn activation is BCR-ABL independent, it is complexed with the Gab2 and c-Cbl adapter/scaffold proteins, and it mediates persistent Gab2 and BCR-ABL tyrosine phosphorylation in the presence or absence of imatinib. Lyn silencing or inhibition is necessary to suppress Gab2 and BCR-ABL phosphorylation and to recover imatinib activity. Lyn also negatively regulates c-Cbl stability, whereas c-Cbl ty- IntroductionBCR-ABL is a constitutively active tyrosine kinase expressed as a consequence of 9:22 chromosomal translocation (Philadelphia chromosome) in a majority of chronic myelogenous leukemia (CML) patients and a subset of patients with acute lymphocytic leukemia (ALL). 1 The role for BCR-ABL in these diseases has been well established by both molecular and animal models 2 and is the basis for target-specific therapy by the tyrosine kinase inhibitor, imatinib (Gleevec, STI-571; Novartis AG, Basel, Switzerland). Imatinib provides very effective control of BCR-ABL-positive leukemias, especially in newly diagnosed patients in whom hematologic and cytogenetic responses are common. 3 Patients with more advanced disease (accelerated phase or blast crisis) have a lower response rate and frequently progress on therapy. 4,5 Reduction in imatinib activity has been linked to changes in BCR-ABL structure and expression (through mutations, deletions, or amplification), [6][7][8] although recent observations have demonstrated that these changes alone do not account for all imatinib failures. [9][10][11][12][13] Other mechanisms, such as engagement of other signaling cascades, loss of tumor suppressor function, acquisition of stem cell-like characteristics, or cellular pharmacology may also play a role in disease progression and imatinib activity. [14][15][16][17][18] CML cell model studies have shown that expression or activation of Src-family kinases (SFKs) may also play a role in imatinib resistance. [19][20][21] Resistance to imatinib in K562 cells occurs in the absence of BCR-ABL point mutations or gene amplification, but correlates with overexpression of Lyn kinase, a SFK whose activity is unaffected by imatinib. 19 Lyn kinase activation increases BCR-ABL phosphorylation, and may prevent BCR-ABL from adopting the inactive conformation that is a prerequisite for imatinib binding. [22][23][24][25] Lyn overexpression is also reported to increase expression of survival genes and suppress apoptosis through a BCR-ABL-independent mechanism. 21 Analysis of clinical specimens demonstrated that Lyn and other SFKs (Hck) are highly activated in blasts from CML patients in a BCR-ABL kinaseindependent fashion, suggesting that persistent Lyn (or other SFK) activation or overexpression may play a role in imatinib resistance. 19 Howe...

Single-particle tracking (SPT) is a powerful method for exploring single-molecule dynamics in living cells with nanoscale spatiotemporal resolution. Photostability and bright fluorescence make quantum dots (Qdots) a popular choice for SPT. However, their large size could potentially alter the mobility of the molecule of interest. To test this, we labelled B cell receptors on the surface of B-lymphocytes with monovalent Fab fragments of antibodies that were either linked to Qdots via streptavidin or directly conjugated to the small organic fluorophore Cy3. Imaging of receptor mobility by total internal reflection fluorescence microscopy (TIRFM), followed by quantitative single-molecule diffusion and confinement analysis, definitively showed that Qdots sterically hinder lateral mobility regardless of the substrate to which the cells were adhered. Qdot labelling also drastically altered the frequency with which receptors transitioned between apparent slow- and fast-moving states and reduced the size of apparent confinement zones. Although we show that Qdot-labelled probes can detect large differences in receptor mobility, they fail to resolve subtle differences in lateral diffusion that are readily detectable using Cy3-labelled Fabs. Our findings highlight the utility and limitations of using Qdots for TIRFM and wide-field-based SPT, and have significant implications for interpreting SPT data.

Caspase recruitment domain (CARD) protein-B cell CLL/lymphoma 10 (BCL10)-MALT1 paracaspase (MALT1) [CBM] complexes are critical signaling adaptors that facilitate immune and inflammatory responses downstream of both cell surface and intracellular receptors. Germline mutations that alter the function of members of this complex (termed CBMopathies) cause a broad array of clinical phenotypes, ranging from profound combined immunodeficiency to B-cell lymphocytosis. With an increasing number of patients being described in recent years, the clinical spectrum of diseases associated with CBM-opathies is rapidly expanding and becoming unexpectedly heterogeneous. Here we review major discoveries that have shaped our understanding of CBM complex biology, and we provide an overview of the clinical presentation, diagnostic approach, and treatment options for those carrying germline mutations affecting CARD9,