Jean S. Oak

Sjögren's syndrome-like disease in mice with T cells lacking class 1A phosphoinositide-3-kinase

Sjögrens syndrome (SS) is an autoimmune disease that is characterized by infiltration of exocrine tissues, resulting in xerostomia (dry mouth) and keratoconjunctivitis sicca (dry eyes). Here, we show that mice with T cell-specific loss of class IA phosphoinositide 3-kinase function develop organ-specific autoimmunity that resembles the human disease SS. Most mutant mice aged 3–8 months develop corneal opacity and eye lesions due to irritation and constant scratching. These mice display cardinal signs of primary SS such as marked lymphocytic infiltration of the lacrimal glands, antinuclear antibodies in the serum, and elevated titer of anti-SS-A antibody, in the absence of kidney pathology. Immunofluorescence studies show the presence of numerous CD4+ T cells with a smaller number of CD8+ T cells and B cells in the lacrimal glands. CD4+ T cells from these mice exhibit aberrant differentiation in vitro. These results indicate that aberrant T cells with impaired class IA phosphoinositide 3-kinase signaling can lead to organ-specific autoimmunity. In addition, the mouse model described here represents a tool to study the pathogenesis and treatment of SS.

Selective inhibition of phosphoinositide 3-kinase p110α preserves lymphocyte function

Background: The class IA PI3K isoform p110α is a promising drug target in cancer therapy yet its role in lymphocytes is not known. Results: Lymphocyte function was minimally affected by p110α inhibition both in vitro and in vivo. Conclusion: Selective inhibition of p110α preserves lymphocyte function. Significance: The study raises confidence that selective p110α inhibitors in cancer therapy will not be immunosuppressive. Class IA phosphoinositide 3-kinase (PI3K) is essential for clonal expansion, differentiation, and effector function of B and T lymphocytes. The p110δ catalytic isoform of PI3K is highly expressed in lymphocytes and plays a prominent role in B and T cell responses. Another class IA PI3K catalytic isoform, p110α, is a promising drug target in cancer but little is known about its function in lymphocytes. Here we used highly selective inhibitors to probe the function of p110α in lymphocyte responses in vitro and in vivo. p110α inhibition partially reduced B cell receptor (BCR)-dependent AKT activation and proliferation, and diminished survival supported by the cytokines BAFF and IL-4. Selective p110δ inhibition suppressed B cell responses much more strongly, yet maximal suppression was achieved by targeting multiple PI3K isoforms. In mouse and human T cells, inhibition of single class IA isoforms had little effect on proliferation, whereas pan-class I inhibition did suppress T cell expansion. In mice, selective p110α inhibition using the investigational agent MLN1117 (previously known as INK1117) did not disrupt the marginal zone B cell compartment and did not block T cell-dependent germinal center formation. In contrast, the selective p110δ inhibitor IC87114 strongly suppressed germinal center formation and reduced marginal zone B cell numbers, similar to a pan-class I inhibitor. These findings show that although acute p110α inhibition partially diminishes AKT activation, selective p110α inhibitors are likely to be less immunosuppressive in vivo compared with p110δ or pan-class I inhibitors.

T Cell Ig and Mucin Domain-1-Mediated T Cell Activation Requires Recruitment and Activation of Phosphoinositide 3-Kinase

Ligation of the transmembrane protein T cell Ig and mucin domain (Tim)-1 can costimulate T cell activation. Agonistic Abs to Tim-1 are also capable of inducing T cell activation without additional stimuli. However, little is known about the biochemical mechanisms underlying T cell stimulation or costimulation through Tim-1. We show that a tyrosine in Tim-1 becomes phosphorylated in a lck-dependent manner, whereupon it can directly recruit p85 adaptor subunits of PI3K. This results in PI3K activation, which is required for Tim-1 function. We also provide genetic evidence that p85 expression is required for optimal Tim-1 function. Thus, we describe a pathway from Tim-1 tyrosine phosphorylation to the PI3K signaling pathway, which appears to be a major effector of Tim-1-mediated T cell activation.

Epstein–Barr virus-induced gene 3 negatively regulates neuroinflammation and T cell activation following coronavirus-induced encephalomyelitis

Abstract Epstein–Barr virus-induced gene 3 (EBI3) associates with p28 and p35 to form the immunomodulatory cytokines IL-27 and IL-35, respectively. Infection of EBI3−/− mice with the neuroadapted JHM strain of mouse hepatitis virus (JHMV) resulted in increased mortality that was not associated with impaired ability to control viral replication but enhanced T cell and macrophage infiltration into the CNS. IFN-γ secretion from virus-specific CD4+ and CD8+ T cells isolated from infected EBI3−/− mice was augmented while IL-10 expression muted in comparison to infected WT mice. These data demonstrate a regulatory role for EBI3-associated cytokines in controlling host responses following CNS viral infection.

Frontline: The p85α isoform of phosphoinositide 3-kinase is essential for a subset of B cell receptor-initiated signaling responses

Phosphoinositide 3‐kinase (PI3K) is a ubiquitously expressed signaling enzyme that plays an integral role in development and activation of B cells. B cell receptor (BCR)‐driven proliferation is completely blocked either in cells lacking the p85α regulatory isoform of PI3K or in wild‐type cells treated with pharmacological PI3K inhibitors. However, the contribution of p85α to early signaling events has not been fully investigated. Here we show that B cells lacking p85α have signaling impairments that are both quantitatively and qualitatively different from those in cells treated with PI3K inhibitors. Loss of p85α results in partial reductions in Ca2+ mobilization and IκB phosphorylation, whereas ERK phosphorylation is not diminished. Moreover, although Akt phosphorylation is partially reduced, phosphorylation of several proteins downstream of Akt is preserved. These partial impairments suggest that there are other routes to PI3K activation in B cells apart from p85α‐associated catalytic subunits. Notably, addition of phorbol ester restores BCR‐mediated proliferation in p85α‐deficient cells but not wild‐type cells treated with PI3K inhibitors. These findings suggest that the primary BCR signaling defect in B cells lacking p85α is a failure to activate diacylglycerol‐regulated signaling enzymes, most likely protein kinase C.

Link between inflammation and aquaporin‐5 distribution in submandibular gland in sjögren’s syndrome?

OBJECTIVE To determine whether a link exists between inflammation and aquaporin-5 distribution in submandibular glands from three animal models for Sjögrens syndrome: IQI/JIC, r1ΔT/r2n and non-obese diabetic mice. METHODS Mice of different ages were used. Inflammatory infiltrates were quantified using the focus score. Acinar aquaporin-5 subcellular distribution was determined by immunohistochemistry and quantified using labelling indices. RESULTS   Minor inflammatory infiltrates were present in r1f/r2n mice. Massive inflammatory infiltrates and acinar destruction were observed in 24-week-old non-obese diabetic mice, 10-and 13-month-old IQI/JIC mice and some r1ΔT/r2n mice. Aquaporin-5 immunoreactivity was primarily apical in submandibular glands from 8- and 24-week-old Balb/C mice, 8-week-old non-obese diabetic mice, 2-, 4- and 7-month-old IQI/JIC mice and r1f/r2n mice. In contrast, decreased apical aquaporin-5 labelling index with concomitant increased apical-basolateral, apical-cytoplasmic and/or apical-basolateral-cytoplasmic aquaporin-5 labelling indices was observed in 24-week-old non-obese diabetic, 10- and 13-month-old IQI/JIC and r1ΔT/r2n mice with a focus score≥1. CONCLUSIONS   Altered aquaporin-5 distribution in submandibular acinar cells from IQI/JIC, non-obese diabetic and r1ΔT/r2n mice with a focus score≥1 appears to be concomitant to the presence of inflammatory infiltrates and acinar destruction.

Lymphocyte cell motility: the twisting, turning tale of phosphoinositide 3-kinase.

The PI3K (phosphoinositide 3-kinase) family of lipid kinases regulate cell motility in diverse organisms and cell types. In mammals, the main PI3K enzyme activated by chemokine receptor signalling is the class IB isoform, p110gamma. Studies of p110gamma-knockout mice have shown an essential function for this isoform in chemotaxis of neutrophils and macrophages both in vitro and in vivo. However, the roles of p110gamma and other PI3K enzymes and regulatory subunits in lymphocyte motility have been more difficult to discern. Recent studies of adoptively transferred, fluorescently labelled lymphocytes have revealed complex and unexpected functions for PI3K in lymphocyte migration in vivo. In this review we highlight cell-type-specific roles for PI3K catalytic and regulatory subunits in the homing and basal motility of lymphocytes in the intact lymph node.

The p85β regulatory subunit of phosphoinositide 3-kinase has unique and redundant functions in B cells

Phosphoinositide kinase (PI3K) is activated by various receptors on lymphocytes and regulates development, activation, and tolerance. Genetic ablation of PI3K function in T cells leads to the appearance of autoimmune disorders. In B cells, loss of the class IA regulatory subunit p85α causes a partial defect in B cell development and proliferation, whereas loss of p85β alone causes no apparent changes in B cell function. Here we investigate further the consequences of p85β deletion in B cells, in the presence or absence of p85α. We demonstrate that p85β partially compensates for loss of p85α in B cell development and peripheral survival, with greater defects observed when both isoforms are absent. BCR-mediated AKT phosphorylation is partially reduced in p85α-deficient B cells and further diminished with concomitant loss of p85β. Unexpectedly, loss of p85β results in increased BCR-mediated proliferation and ERK phosphorylation. These results indicate that the p85β regulatory isoform has partially overlapping functions with p85α in B cells as well as a unique role in opposing BCR responses.

Role of phosphoinositide 3-kinase signaling in autoimmunity

Activation of the phosphoinositide 3-kinase (PI3K) pathway promotes proliferation and survival in many different cell types of the immune system. PI3K acts downstream of receptors that mediate proliferation and survival in T cells, and required roles for individual class I PI3K catalytic isoforms have been established. Interestingly, mice with either augmented or diminished PI3K activity in T cells develop lymphoproliferation and signs of autoimmunity. Here, we summarize our current knowledge of mouse strains with hyperactive or reduced PI3K, different isoforms of class I PI3K in T cell-mediated immunity and autoimmunity, and the therapeutic implications for modulating this pathway for treatment of various autoimmune diseases.