S. M. Shahjahan Miah

Point mutations of 3BP2 identified in human‐inherited disease cherubism result in the loss of function

Adaptor protein 3BP2 positively regulates the high affinity IgE receptor (FcɛRI)‐mediated activation of degranulation in mast cells. Genetic study identified the point mutations of 3BP2 gene in human‐inherited disease cherubism. The multiple cysts in cherubism lesion of jaw bones are filled with the activated osteoclasts and stromal cells, including mast cells. By over‐expression study using rat basophilic leukaemia RBL‐2H3 mast cells, we have analysed the effect of the point mutations on the function of 3BP2 protein, which plays a positive regulatory role on FcɛRI‐mediated mast cell activation. Over‐expression of 3BP2 mutants suppressed the antigen‐induced degranulation and cytokine gene transcription. Antigen‐induced phosphorylation of Vav1, activation of Rac1, extracellular signal regulated kinase (ERK), c‐Jun N‐terminal kinase (JNK), p38 mitogen activated protein kinase (MAPK), inhibitor of nuclear factor κB kinase (IKK) and nuclear factor of activated T cells (NFAT) were all impaired in the cells over‐expressing the cherubism mutants of 3BP2. Furthermore, cherubism mutations of 3BP2 may abrogate the binding ability to interact with chaperone protein 14‐3‐3. These results demonstrate that over‐expression of the mutant form of 3BP2 inhibits the antigen‐induced mast cell activation. It suggests that point mutations of 3BP2 gene cause the dysfunction of 3BP2 in vivo.

Negative regulation of Lyn protein-tyrosine kinase by c-Cbl ubiquitin-protein ligase in FcεRI-mediated mast cell activation

Background: Recent studies have demonstrated that c‐Cbl functions as a ubiquitin‐protein ligase toward immune receptors and non‐receptor protein‐tyrosine kinase Syk by facilitating their ubiquitination and subsequent targeting to proteasomes. However, it was not clear whether Src family kinase Lyn is regulated by the Cbl family of ubiquitin‐protein ligases.

Activation of Syk Protein Tyrosine Kinase in Response to Osmotic Stress Requires Interaction with p21-Activated Protein Kinase Pak2/γ-PAK

ABSTRACT The p21-activated serine/threonine protein kinase Pak2/γ-PAK and the nonreceptor type of protein tyrosine kinase Syk are known to be activated when the cells are exposed to osmotic stress. The purpose of the present study was to examine whether Pak2 and Syk functionally cooperate in cellular signaling. Cotransfection studies revealed that Pak2 associates with Syk in COS cells. The constitutively active form of Cdc42 increases the association of Pak2 with Syk. Pak2 coexpressed with an inactive form of Cdc42 or kinase-inactive Pak2 interacts to a lesser extent with Syk, suggesting that Pak2-Syk association is enhanced by Pak2 activation. Interaction with Pak2 enhances the intrinsic kinase activity of Syk. This is supported by in vitro studies showing that Pak2 phosphorylates and activates Syk. Treatment of cells with sorbitol to induce hyperosmolarity results in the translocation of Pak2 and Syk to the region surrounding the nucleus and in dramatic enhancement of their association. Furthermore, cotransfection of Pak2 and Syk leads to the activation of c-Jun N-terminal kinase (JNK) under hyperosmotic conditions. Pak2 short interfering RNA suppresses sorbitol-mediated activation of endogenous Syk and JNK, thus identifying a novel pathway for JNK activation by Cdc42. These results demonstrate that Pak2 and Syk positively cooperate to regulate cellular responses to stress.

Role of Type I Interferon Receptor Signaling on NK Cell Development and Functions

Type I interferons (IFN) are unique cytokines transcribed from intronless genes. They have been extensively studied because of their anti-viral functions. The anti-viral effects of type I IFN are mediated in part by natural killer (NK) cells. However, the exact contribution of type I IFN on NK cell development, maturation and activation has been somewhat difficult to assess. In this study, we used a variety of approaches to define the consequences of the lack of type I interferon receptor (IFNAR) signaling on NK cells. Using IFNAR deficient mice, we found that type I IFN affect NK cell development at the pre-pro NK stage. We also found that systemic absence of IFNAR signaling impacts NK cell maturation with a significant increase in the CD27+CD11b+ double positive (DP) compartment in all organs. However, there is tissue specificity, and only in liver and bone marrow is the maturation defect strictly dependent on cell intrinsic IFNAR signaling. Finally, using adoptive transfer and mixed bone marrow approaches, we also show that cell intrinsic IFNAR signaling is not required for NK cell IFN-γ production in the context of MCMV infection. Taken together, our studies provide novel insights on how type I IFN receptor signaling regulates NK cell development and functions.

Ptpn11 Deletion in CD4+ Cells Does Not Affect T Cell Development and Functions but Causes Cartilage Tumors in a T Cell-Independent Manner

The ubiquitously expressed tyrosine phosphatase Src homology region 2 domain-containing phosphatase-2 (SHP-2, encoded by Ptpn11) is required for constitutive cellular processes including proliferation, differentiation, and the regulation of immune responses. During development and maturation, subsets of T cells express a variety of inhibitory receptors known to associate with phosphatases, which in turn, dephosphorylate key players of activating receptor signaling pathways. We hypothesized that SHP-2 deletion would have major effects on T cell development by altering the thresholds for activation, as well as positive and negative selection. Surprisingly, using mice conditionally deficient for SHP-2 in the T cell lineage, we show that the development of these lymphocytes is globally intact. In addition, our data demonstrate that SHP-2 absence does not compromise T cell effector functions, suggesting that SHP-2 is dispensable in these cells. Unexpectedly, in aging mice, Ptpn11 gene deletion driven by CD4 Cre recombinase leads to cartilage tumors in wrist bones in a T cell-independent manner. These tumors resemble miniature cartilaginous growth plates and contain CD4-lineage positive chondrocyte-like cells. Altogether these results indicate that SHP-2 is a cartilage tumor suppressor during aging.