Erik J. Peterson

Adaptor proteins in lymphocyte antigen-receptor signaling.

Adaptor molecules, proteins that possess no intrinsic enzymatic function, but which mediate protein-protein interactions, have a critical role in integrating signal transduction pathways following engagement of cell-surface receptors. Several newly described adaptor molecules have been shown to serve important functions in the regulation of signaling events initiated by lymphocyte antigen receptors. Understanding how these adaptor proteins function to modulate signaling cascades will provide important insights into the complex biology of lymphocyte activation.

Gene expression profiling in human autoimmunity

Summary:  Human autoimmune diseases are well suited for the application of gene expression profiling. Sampling of blood cells and target tissues has already revealed many important pathways contributing to this spectrum of disorders, and many commonalities are emerging. For instance, clinically distinct diseases such as systemic lupus erythematosus, Sjögrens syndrome, dermatomyositis, and psoriasis all show evidence for dysregulation of the type I interferon pathway. These data suggest that autoimmune diseases will eventually be categorized at the level of gene expression. This work has led to advances in our understanding of disease pathogenesis and in the future promises to facilitate assessments of disease activity and improve targeting of therapies. Here, we review the literature on gene profiling in human autoimmune diseases and provide perspective on the current state of the art.

Serum and urinary interleukin-6 in systemic lupus erythematosus

Dysregulation of IL-6 production has been proposed as a pathogenic mechanism in SLE. We asked if serum or urine IL-6 levels could serve as indicators of systemic lupus erythematosus (SLE) disease activity. Using a sensitive enzyme-linked immunosorbent assay (ELISA), we measured serum and urine IL-6 in 56 SLE patients. Disease activity was assessed using a standard clinical index, the Systemic Lupus Activity Measure (SLAM). Only seven of 56 SLE patients had elevated serum IL-6 levels, compared with 1 of 32 controls (NS). SLE disease activity did not correlate with serum IL-6 levels. Sixteen of 50 SLE patients in whom urine IL-6 was measured exhibited elevated urine IL-6 levels, compared with 1 of 17 controls (p = < 0.05). Urine IL-6 levels correlated with overall disease activity and with the presence of active urinary sediment. Our results indicate that serum IL-6 is not a predictor of disease activity in SLE, but that urine IL-6 may be a marker of active nephritis.

Tyrosine Phosphatase PTPN22: Multifunctional Regulator of Immune Signaling, Development, and Disease

Inheritance of a coding variant of the protein tyrosine phosphatase nonreceptor type 22 (PTPN22) gene is associated with increased susceptibility to autoimmunity and infection. Efforts to elucidate the mechanisms by which the PTPN22-C1858T variant modulates disease risk revealed that PTPN22 performs a signaling function in multiple biochemical pathways and cell types. Capable of both enzymatic activity and adaptor functions, PTPN22 modulates signaling through antigen and innate immune receptors. PTPN22 plays roles in lymphocyte development and activation, establishment of tolerance, and innate immune cell-mediated host defense and immunoregulation. The disease-associated PTPN22-R620W variant protein is likely involved in multiple stages of the pathogenesis of autoimmunity. Establishment of a tolerant B cell repertoire is disrupted by PTPN22-R620W action during immature B cell selection, and PTPN22-R620W alters mature T cell responsiveness. However, after autoimmune attack has initiated tissue injury, PTPN22-R620W may foster inflammation through modulating the balance of myeloid cell-produced cytokines.

Changes in Novel Biomarkers of Disease Activity in Juvenile and Adult Dermatomyositis are Sensitive Biomarkers of Disease Course

OBJECTIVE Muscle enzyme levels are insensitive markers of disease activity in juvenile and adult dermatomyositis (DM), especially during the active treatment phase. To improve our ability to monitor DM disease activity longitudinally, especially in the presence of immunomodulating agents, we prospectively evaluated whether interferon (IFN)-dependent peripheral blood gene and chemokine signatures could serve as sensitive and responsive biomarkers for change in disease activity in adult and juvenile DM. METHODS Peripheral blood and clinical data were collected from 51 patients with juvenile or adult DM prospectively over 2 study visits. We performed disease activity measurements and calculated whole-blood type I IFN gene and chemokine scores. We also measured serum levels of other proinflammatory cytokines, including interleukin-6 (IL-6). RESULTS Changes in juvenile and adult DM global disease activity correlated positively and significantly with changes in the type I IFN gene score before adjustment for medication use (r = 0.33, P = 0.023) and with changes in the IFN chemokine score before and after adjustment for medication use (r = 0.53, P < 0.001 and r = 0.50, P < 0.001, respectively). Changes in muscle and extramuscular visual analog scale (VAS) scores correlated positively with changes in IFN gene and chemokine scores (P = 0.002, P < 0.001, P = 0.095, P < 0.001). Serum levels of IL-6, IL-8, and tumor necrosis factor α (TNFα) correlated positively with changes in global, muscle, and extramuscular VAS scores (P < 0.05). CONCLUSION Our findings suggest that changes in type I IFN gene and chemokine scores as well as in levels of IL-6, IL-8, and TNFα may serve as sensitive and responsive longitudinal biomarkers of change in disease activity in juvenile and adult DM, even in the presence of immunomodulating agents.

NK CYTOKINE SECRETION AND CYTOTOXICITY OCCUR INDEPENDENTLY OF THE SLP-76 ADAPTOR PROTEIN

The adapter protein SLP‐76 is required for T cell development and TCR signal transduction. SLP‐76 is also expressed in NK cells, yet splenic populations of NK cells develop normally in SLP‐76‐deficient mice. We examined the effects of SLP‐76 deficiency upon cellular activation through studies of NK function in SLP‐76–/– mice. This study presents evidence that NK populations in both spleen and liver of SLP‐76–/– mice remain intact. Natural cytotoxic responses of SLP‐76–/– splenocytes proceed in a manner comparable to those of wild‐type control splenocytes. Similar to controls, SLP‐76–/– splenocytes exhibit enhanced survival and augmented cytotoxic capacity after in vitro culture with IL‐2. IL‐2‐stimulated SLP‐76–/– splenocytes also retain normal antibody‐dependent cellular cytotoxicity and the ability to secrete IFN‐γ in response to IL‐12 stimulation. These results indicate that, unlike events stimulated by TCR engagement, signaling cascades engaged by IL‐2 and IL‐12 receptors, by FcγRIIIA (which mediates antibody‐dependent cellular cytotoxicity), and by natural cytotoxicity‐associated receptors on murine NK cells can occur independently of SLP‐76.

Signaling by Fyn-ADAP via the Carma1-Bcl-10-MAP3K7 signalosome exclusively regulates inflammatory cytokine production in NK cells.

Inflammation is a critical component of the immune response. However, acute or chronic inflammation can be highly destructive. Uncontrolled inflammation forms the basis for allergy, asthma and various autoimmune disorders. Here we identified a signaling pathway that was exclusively responsible for the production of inflammatory cytokines but not for cytotoxicity. Recognition of tumor cells expressing the NK cell–activatory ligands H60 or CD137L by mouse natural killer (NK) cells led to efficient cytotoxicity and the production of inflammatory cytokines. Both of those effector functions required the kinases Lck, Fyn and PI(3)K (subunits p85α and p110δ) and the signaling protein PLC-γ2. However, a complex of Fyn and the adaptor ADAP exclusively regulated the production of inflammatory cytokines but not cytotoxicity in NK cells. That unique function of ADAP required a Carma1–Bcl-10–MAP3K7 signaling axis. Our results have identified molecules that can be targeted to regulate inflammation without compromising NK cell cytotoxicity.

Differential Requirement for Adapter Proteins Src Homology 2 Domain-Containing Leukocyte Phosphoprotein of 76 kDa and Adhesion- and Degranulation-Promoting Adapter Protein in FcεRI Signaling and Mast Cell Function

The adapter molecule Src homology 2 (SH2) domain-containing leukocyte phosphoprotein of 76 kDa (SLP-76) is essential for FcεRI-mediated signaling, degranulation and IL-6 production in mast cells. To test the structural requirements of SLP-76 in mast cell signaling and function, we have studied the functional responses of murine bone marrow-derived mast cells (BMMCs) expressing mutant forms of SLP-76. We found that the N-terminal tyrosines as well as the central proline-rich region of SLP-76 are required for participation of SLP-76 in FcεRI-mediated signaling and function. The C-terminal SH2 domain of SLP-76 also contributes to optimal function of SLP-76 in mast cells. Another adapter molecule, adhesion- and degranulation-promoting adapter protein (ADAP), is known to bind the SH2 domain of SLP-76, and cell line studies have implicated ADAP in mast cell adhesion and FcεRI-induced degranulation. Surprisingly, we found that mast cells lacking ADAP expression demonstrate no defects in FcεRI-induced adhesion, granule release, or IL-6 production, and that ADAP-deficient mice produce a normal passive systemic anaphylactic response. Thus, failure to bind ADAP does not underlie the functional defects exhibited by SLP-76 SH2 domain mutant-expressing mast cells.

The TCR ADAPts to integrin-mediated cell adhesion.

Summary: Adapter proteins regulate leukocyte signal transduction through recruitment of effector molecules to multiprotein complexes. Recent studies in Adhesion and Degranulation promoting Adapter Protein (ADAP)‐deficient mice have established that the cytoplasmic phosphoprotein ADAP is required for optimal, mature T‐cell proliferation. Furthermore, ADAP plays a key role in T‐cell antigen receptor (TCR)‐mediated ‘inside out’ signaling leading to integrin activation and to enhanced cellular adhesion to integrin ligands. ADAP associates physically with molecules known to play roles in the regulation of TCR‐stimulated actin polymerization. These associations support the hypothesis that ADAP functions in actin cytoskeletal reorganization leading to cellular adhesion and activation.

Adhesion and Degranulation-Promoting Adapter Protein (ADAP) Positively Regulates T Cell Sensitivity to Antigen and T Cell Survival

The hemopoietic specific adapter protein ADAP (adhesion and degranulation-promoting adapter protein) positively regulates TCR-dependent, integrin-mediated adhesion and participates in signaling pathways downstream of the TCR that result in T cell activation. The specific role of ADAP in regulating Ag-dependent T cell interactions with APCs and T cell activation following Ag stimulation is not known. We used ADAP−/− DO11.10 T cells to demonstrate that ADAP promotes T cell conjugation to Ag-laden APCs. Complementary in vitro and in vivo approaches reveal that ADAP controls optimal T cell proliferation, cytokine production, and expression of the prosurvival protein Bcl-xL in response to limiting Ag doses. Furthermore, ADAP is critical for clonal expansion in vivo independent of Ag concentration under conditions of low clonal abundance. These results suggest that ADAP regulates T cell activation by promoting Ag-dependent T cell-APC interactions, resulting in enhanced T cell sensitivity to Ag, and by participating in prosurvival signaling pathways initiated by Ag stimulation.