Phosphoinositide 3-kinase knockout mice: role of p85alpha in B cell development and proliferation

PI3K-p110α mediates the oncogenic activity induced by loss of the novel tumor suppressor PI3K-p85α

Mutation or loss of the p85 regulatory subunit of phosphatidylinositol 3-kinase (PI3K) is emerging as a transforming factor in cancer, but the mechanism of transformation has been controversial. Here we find that hemizygous deletion of the PIK3R1 gene encoding p85α is a frequent event in breast cancer, with PIK3R1 expression significantly reduced in breast tumors. PIK3R1 knockdown transforms human mammary epithelial cells, and genetic ablation of Pik3r1 accelerates a mouse model of HER2/neu-driven breast cancer. We demonstrate that partial loss of p85α increases the amount of p110α-p85 heterodimers bound to active receptors, augmenting PI3K signaling and oncogenic transformation. Pan-PI3K and p110α-selective pharmacological inhibition effectively blocks transformation driven by partial p85α loss both in vitro and in vivo. Together, our data suggest that p85α plays a tumor-suppressive role in transformation, and suggest that p110α-selective therapeutics may be effective in the treatment of breast cancer patients with PIK3R1 loss.

Signaling in Effector Lymphocytes: Insights toward Safer Immunotherapy

Receptors on T and NK cells systematically propagate highly complex signaling cascades that direct immune effector functions, leading to protective immunity. While extensive studies have delineated hundreds of signaling events that take place upon receptor engagement, the precise molecular mechanism that differentially regulates the induction or repression of a unique effector function is yet to be fully defined. Such knowledge can potentiate the tailoring of signal transductions and transform cancer immunotherapies. Targeted manipulations of signaling cascades can augment one effector function such as antitumor cytotoxicity while contain the overt generation of pro-inflammatory cytokines that contribute to treatment-related toxicity such as “cytokine storm” and “cytokine-release syndrome” or lead to autoimmune diseases. Here, we summarize how individual signaling molecules or nodes may be optimally targeted to permit selective ablation of toxic immune side effects.

Mal, more than a bridge to MyD88

The family of type 1 transmembrane proteins known as Toll-like receptors (TLRs) provide early immune system recognition and response to infection. In order to transmit their signal to the nucleus and initiate activation of pro-inflammatory and anti-microbial genes, TLRs must initiate a cytoplasmic signalling cascade, which is alternately controlled by 6 known signalling adaptors. These signaling adaptors are crucial for activating the correct immune response to any given TLR / pathogen interaction. This review will focus on one of those adaptors, MyD88 adaptor-like (Mal), also known as TIRAP. Mal is critical for signalling by the best studied of the TLRs, the Gram negative bacterial lipopolysaccharide (LPS) sensor, TLR4. Mal's role in TLR2 signalling in response to activation of the bacterial lipopeptide receptor, TLR2, is more contentious. Mal is a component of the so-called 'MyD88-dependent pathway' in TLR4 signalling. Recent advances in our understanding of the signalling pathways downstream of Mal highlight MyD88-indpendent roles, thus positioning Mal as multifunctional and integral for the molecular control of bacterial infections as well as inflammatory diseases. Here we describe the sequence of molecular events involved in the signalling pathways controlled by Mal, and the importance of Mal in driving host protection against a variety of bacteria, with specific attention to the evidence for Mal's role in TLR2 signalling, recent structural findings that have altered our understanding of Mal signalling, and evidence that single nucleotide polymorphisms (SNPs) of Mal are responsible for variations in population level resistance and susceptibility to bacterial infection.

New frontiers of primary antibody deficiencies

Primary antibody deficiencies (PAD) form the largest group of inherited disorders of the immune system. They are characterized by a marked reduction or absence of serum immunoglobulins (Ig) due to disturbed B cell differentiation and by a poor response to vaccination. PAD can be divided into agammaglobulinemia, Ig class switch recombination deficiencies, and idiopathic hypogammaglobulinemia. Over the past 20 years, defects have been identified in 18 different genes, but in many PAD patients the underlying gene defects have not been found. Diagnosis of known PAD and discovery of new PAD is important for good patient care. In this review, we present the effects of genetic defects in the context of normal B cell differentiation, and we discuss how new technical developments can support understanding and discovering new genetic defects in PAD.

Inositol pyrophosphates inhibit Akt signaling, thereby regulating insulin sensitivity and weight gain

The inositol pyrophosphate IP7 (5-diphosphoinositolpentakisphosphate), formed by a family of three inositol hexakisphosphate kinases (IP6Ks), modulates diverse cellular activities. We now report that IP7 is a physiologic inhibitor of Akt, a serine/threonine kinase that regulates glucose homeostasis and protein translation, respectively, via the GSK3β and mTOR pathways. Thus, Akt and mTOR signaling are dramatically augmented and GSK3β signaling reduced in skeletal muscle, white adipose tissue, and liver of mice with targeted deletion of IP6K1. IP7 affects this pathway by potently inhibiting the PDK1 phosphorylation of Akt, preventing its activation and thereby affecting insulin signaling. IP6K1 knockout mice manifest insulin sensitivity and are resistant to obesity elicited by high-fat diet or aging. Inhibition of IP6K1 may afford a therapeutic approach to obesity and diabetes.

Polysaccharides from the root of Angelica sinensis promotes hematopoiesis and thrombopoiesis through the PI3K/AKT pathway

Background

Dozens of Traditional Chinese Medicine (TCM) formulas have been used for promotion of "blood production" for centuries, and we are interested in developing novel thrombopoietic medicines from these TCMs. Our previous studies have demonstrated the hematopoietic effects of DangGui BuXue Tong (DBT), a formula composed of Radix Angelicae Sinensis and Radix Astragali in animal and cellular models. As a step further to identify and characterize the active chemical components of DBT, we tested the hematopoietic and particularly, thrombopoietic effects of polysaccharide-enriched fractions from the root of Radix Angelicae Sinensis (APS) in this study.

Methods

A myelosuppression mouse model was treated with APS (10 mg/kg/day). Peripheral blood cells from APS, thrombopoietin and vehicle-treated samples were then counted at different time-points. Using the colony-forming unit (CFU) assays, we determined the effects of APS on the proliferation and differentiation of hematopoietic stem/progenitor cells and megakaryocytic lineages. Using a megakaryocytic cell line M-07e as model, we analyzed the cellular apoptosis progression with and without APS treatment by Annexin V, Mitochondrial Membrane Potential and Caspase 3 assays. Last, the anti-apoptotic effect of APS on cells treated with Ly294002, a Phosphatidylinositol 3-Kinse inhibitor (PI3K) was also tested.

Results

In animal models, APS significantly enhanced not only the recovery of platelets, other blood cells and their progenitor cells, but also the formation of Colony Forming Unit (CFU). In M-07e cells, we observed the anti-apoptotic effect of APS. Treatment by Ly294002 alone increased the percentage of cells undergoing apoptosis. However, addition of APS to Ly294002-treated cells significantly reduced the percentage of cells undergoing apoptosis.

Conclusions

APS promotes hematopoiesis and thrombopoiesis in the mouse model. This effect likely resulted from the anti-apoptosis activity of APS and is likely to involve the PI3K/AKT pathway.

Nf1-/- Schwann cell-conditioned medium modulates mast cell degranulation by c-Kit-mediated hyperactivation of phosphatidylinositol 3-kinase

Neurofibromatosis type 1 (NF1) is a common genetic disorder and is characterized by both malignant and nonmalignant neurofibromas, which are composed of Schwann cells, degranulating mast cells, fibroblasts, and extracellular matrix. We and others have previously shown that hyperactivation of the c-Kit pathway in an Nf1 haploinsufficient microenvironment is required for both tumor formation and progression. Mast cells play a key role in both tumorigenesis and neoangiogenesis via the production of matrix metalloproteinases, heparin, and a range of different growth factors. In the present study, we show that tumorigenic Schwann cells derived from Nf1(-/-) embryos promote increased degranulation of Nf1(+/-) mast cells compared with wild-type mast cells via the secretion of the Kit ligand. Furthermore, we used genetic intercrosses as well as pharmacological agents to link the hyperactivation of the p21(Ras)-phosphatidylinositol 3-kinase (PI3K) pathway to the increased degranulation of Nf1(+/-) mast cells both in vitro and in vivo. These studies identify the p21(Ras)-PI3K pathway as a major regulator of the gain in Nf1(+/-) mast cell degranulation in neurofibromas. Collectively, these studies identify both c-Kit and PI3K as molecular targets that modulate mast cell functions in cases of NF1.

Myc stimulates B lymphocyte differentiation and amplifies calcium signaling

Deregulated expression of the Myc family of transcription factors (c-, N-, and L-myc) contributes to the development of many cancers by a mechanism believed to involve the stimulation of cell proliferation and inhibition of differentiation. However, using B cell-specific c-/N-myc double-knockout mice and E(mu)-myc transgenic mice bred onto genetic backgrounds (recombinase-activating gene 2-/- and Btk-/- Tec-/-) whereby B cell development is arrested, we show that Myc is necessary to stimulate both proliferation and differentiation in primary B cells. Moreover, Myc expression results in sustained increases in intracellular Ca2+ ([Ca2+]i), which is required for Myc to stimulate B cell proliferation and differentiation. The increase in [Ca2+]i correlates with constitutive nuclear factor of activated T cells (NFAT) nuclear translocation, reduced Ca2+ efflux, and decreased expression of the plasma membrane Ca2+-adenosine triphosphatase (PMCA) efflux pump. Our findings demonstrate a revised model whereby Myc promotes both proliferation and differentiation, in part by a remarkable mechanism whereby Myc amplifies Ca2+ signals, thereby enabling the concurrent expression of Myc- and Ca2+-regulated target genes.

Cell target genes of Epstein-Barr virus transcription factor EBNA-2: induction of the p55alpha regulatory subunit of PI3-kinase and its role in survival of EREB2.5 cells

Microarray analysis covering most of the annotated RNAs in the human genome identified a panel of genes induced by the Epstein-Barr virus (EBV) EBNA-2 transcription factor in the EREB2.5 human B-lymphoblastoid cell line without the need for any intermediate protein synthesis. Previous data indicating that PIK3R1 RNA (the alpha regulatory subunit of PI3-kinase) was induced were confirmed, but it is now shown that it is the p55alpha regulatory subunit that is induced. Several EBV-immortalized lymphoblastoid cell lines were shown to express p55alpha. Expression of PI3-kinase p85 regulatory and p110 catalytic subunits was not regulated by EBNA-2. Proliferation of EREB2.5 lymphoblastoid cells was inhibited by RNAi knock-down of p55alpha protein expression, loss of p55alpha being accompanied by an increase in apoptosis. p55alpha is thus a functional target of EBNA2 in EREB2.5 cells and the specific regulation of p55alpha by EBV will provide an opportunity to investigate the physiological function of p55alpha in this human cell line.

Mouse paneth cell secretory responses to cell surface glycolipids of virulent and attenuated pathogenic bacteria

Mouse Paneth cells respond to bacteria and bacterial cell surface antigens by discharging secretory granules into the lumen of small intestinal crypts (T. Ayabe et al., Nat. Immunol. 1:113-118, 2000). To investigate mechanisms regulating these responses, purified surface glycolipid molecules with known acyl chain modifications and attenuated properties were tested for the ability to stimulate Paneth cell secretion. The antigens included lipopolysaccharide (LPS) from wild-type and msbB-null Escherichia coli and phoP-null and phoP-constitutive Salmonella enterica serovar Typhimurium strains, as well as LPS, lipid A, and lipoteichoic acid from Pseudomonas aeruginosa and Listeria monocytogenes grown in Mg2+-limited media. Measurements of total secreted protein, secreted lysozyme, and the bactericidal peptide activities of collected secretions showed that the purified antigens elicited similar secretory responses from Paneth cells in mouse crypts ex vivo, regardless of glycolipid acyl chain modification. Despite their impaired Tlr4 pathway, Paneth cells in ex vivo C3H/HeJ mouse crypts released equivalent amounts of bactericidal peptide activity in response to purified bacterial antigens, including lipid A. Thus, mouse Paneth cells respond equivalently to purified bacterial cell envelope glycolipids, regardless of functional Tlr4, the structural properties of glycolipid acyl chains, or their association with virulence in humans.

JAK/STAT, Raf/MEK/ERK, PI3K/Akt and BCR-ABL in cell cycle progression and leukemogenesis

The roles of the JAK/STAT, Raf/MEK/ERK and PI3K/Akt signal transduction pathways and the BCR-ABL oncoprotein in leukemogenesis and their importance in the regulation of cell cycle progression and apoptosis are discussed in this review. These pathways have evolved regulatory proteins, which serve to limit their proliferative and antiapoptotic effects. Small molecular weight cell membrane-permeable drugs that target these pathways have been developed for leukemia therapy. One such example is imatinib mesylate, which targets the BCR-ABL kinase as well as a few structurally related kinases. This drug has proven to be effective in the treatment of CML patients. However, leukemic cells have evolved mechanisms to become resistant to this drug. A means to combat drug resistance is to target other prominent signaling components involved in the pathway or to inhibit BCR-ABL by other mechanisms. Treatment of imatinib-resistant leukemia cells with drugs that target Ras (farnysyl transferase inhibitors) or with the protein destabilizer geldanamycin has proven to be a means to inhibit the growth of resistant cells. This review will tie together three important signal transduction pathways involved in the regulation of hematopoietic cell growth and indicate how their expression is dysregulated by the BCR-ABL oncoprotein.

The B cell SH2/PH domain-containing adaptor Bam32/DAPP1 is required for T cell-independent II antigen responses

BACKGROUND

Bam32/DAPP1 is a B cell adaptor composed of both a PH and an SH2 domain. Previous studies in cell culture and chicken DT40 cells have indicated that Bam32 is critical for normal signaling downstream of the B cell receptor (BCR).

RESULTS

We now study the function of Bam32 in mice in which Bam32 has been disrupted by a viral gene trap approach. Although B and T cell development is normal in Bam32(-/-) mice, B cell proliferation is reduced by about 50% after BCR crosslinking when compared with Bam32(+/+) mice. Differences in the activation of Erk, Jnk and p38 Map kinases, PLCgamma, and Ca(2+) flux do not account for the defect in proliferation as activation was similar in Bam32(+/+) and Bam32(-/-) B cells. Interestingly, whereas antibody response to T-dependent (TD) and T-independent (TI)-I antigens was similar between Bam32(+/+) and Bam32(-/-) mice, TI-II responses were defective in Bam32(-/-) mice; Bam32(-/-) mice failed to undergo isotype class switch recombination (CSR) to produce IgG3 antibodies due to a cell-autonomous defect in generation of IgG3 germline transcripts. The defect in TI-II antigen response led to an impaired antibody response to immunization with type 3 Streptococcus pneumoniae capsular polyschaccharide (PS), resulting in a markedly increased susceptibility to infection by Streptococcus pneumoniae.

CONCLUSIONS

These findings indicate that Bam32 specifically couples an upstream signal to the IgG3 isotype heavy chain CSR and suggest that defects in Bam32 may account for the increased susceptibility to encapusulated organisms in a subset of immunodeficient patients.

Reciprocal modulation of Toll-like receptor-4 signaling pathways involving MyD88 and phosphatidylinositol 3-kinase/AKT by saturated and polyunsaturated fatty acids

Toll-like receptor-4 (TLR4) can be activated by nonbacterial agonists, including saturated fatty acids. However, downstream signaling pathways activated by nonbacterial agonists are not known. Thus, we determined the downstream signaling pathways derived from saturated fatty acid-induced TLR4 activation. Saturated fatty acid (lauric acid)-induced NFkappaB activation was inhibited by a dominant-negative mutant of TLR4, MyD88, IRAK-1, TRAF6, or IkappaBalpha in macrophages (RAW264.7) and 293T cells transfected with TLR4 and MD2. Lauric acid induced the transient phosphorylation of AKT. LY294002, dominant-negative (DN) phosphatidylinositol 3-kinase (PI3K), or AKT(DN) inhibited NFkappaB activation, p65 transactivation, and cyclooxygenase-2 (COX-2) expression induced by lauric acid or constitutively active (CA) TLR4. AKT(DN) blocked MyD88-induced NFkappaB activation, suggesting that AKT is a MyD88-dependent downstream signaling component of TLR4. AKT(CA) was sufficient to induce NFkappaB activation and COX-2 expression. These results demonstrate that NFkappaB activation and COX-2 expression induced by lauric acid are at least partly mediated through the TLR4/PI3K/AKT signaling pathway. In contrast, docosahexaenoic acid (DHA) inhibited the phosphorylation of AKT induced by lipopolysaccharide or lauric acid. DHA also suppressed NFkappaB activation induced by TLR4(CA), but not MyD88(CA) or AKT(CA), suggesting that the molecular targets of DHA are signaling components upstream of MyD88 and AKT. Together, these results suggest that saturated and polyunsaturated fatty acids reciprocally modulate the activation of TLR4 and its downstream signaling pathways involving MyD88/IRAK/TRAF6 and PI3K/AKT and further suggest the possibility that TLR4-mediated target gene expression and cellular responses are also differentially modulated by saturated and unsaturated fatty acids.

Distinctions between c-Rel and other NF-kappaB proteins in immunity and disease

c-Rel is a proto-oncogene first identified as the cellular counterpart of the v-Rel oncogene derived from the avian reticuloendotheliosis retrovirus (REV-T). It was subsequently discovered that c-Rel belongs to the NF-kappaB/Rel transcription factor family whose members share a common DNA recognition motif and similar signaling pathways. Despite the similarities, however, each NF-kappaB/Rel member possesses unique properties with regard to tissue expression pattern, response to receptor signals and target gene specificity. These differences are fairly evident from the non-redundant phenotypes exhibited by individual NF-kappaB/Rel knockout mice. Hence the work described in this review will compare and contrast the various physiological functions of c-Rel to those of other NF-kappaB members, particularly with respect to the regulation of proliferation, survival and effector functions in multiple hematopoietic and immunological cell types. The study of c-Rel knockout mice in several disease models will also be discussed as they reveal an important role for c-Rel in response to allergens, auto-antigens, allo-antigens and pathogenic infection.

Epstein-Barr virus latent membrane protein 1 (LMP1) activates the phosphatidylinositol 3-kinase/Akt pathway to promote cell survival and induce actin filament remodeling

The Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) is an integral membrane protein that functions as a constitutively activated member of the tumor necrosis factor receptor family. Whereas LMP1 has been shown to activate the NF-kappaB and mitogen-activated protein kinase pathways, these effects alone are unable to account for the profound oncogenic properties of LMP1. Here we show that LMP1 can activate phosphatidylinositol 3-kinase (PI3K), a lipid kinase responsible for activating a diverse range of cellular processes in response to extracellular stimuli. LMP1 was found to stimulate PI3K activity inducing phosphorylation and subsequent activation of Akt, a downstream target of PI3K responsible for promoting cell survival. Treatment of LMP1-expressing cells with the PI3K inhibitor LY294002 resulted in decreased cell survival. The tumor necrosis factor receptor-associated factor-binding domain of LMP1 was found to be responsible for PI3K activation. The ability of LMP1 to induce actin stress-fiber formation, a Rho GTPase-mediated phenomenon, was also dependent on PI3K activation. These data implicate PI3K activation in many of the LMP1-induced phenotypic effects associated with transformation and suggests that this pathway contributes both to the oncogenicity of this molecule and its role in the establishment of persistent EBV infection.

BCR signal through alpha 4 is involved in S6 kinase activation and required for B cell maturation including isotype switching and V region somatic hypermutation

alpha 4 potentially mediates BCR signals through a rapamycin-sensitive TOR pathway. To investigate a potential role for alpha 4 in B cell activation, the alpha 4 gene was disrupted conditionally in B cells by mating male CD19-Cre mice with female alpha 4-floxed mice. CD19-Cre+/alpha 4flox mice showed loss of alpha 4 protein in B lineage cells and a decreased number of phenotypically normal mature B cells. Compared to normal B cells, alpha 4(-) B cells showed a decreased proliferation in response to the B cell stimulants (anti-IgM antibody plus IL-4, anti-CD40 mAb and lipopolysaccharide), and a reduced S6 kinase activation and rapamycin sensitivity. While CD19-Cre+/alpha 4flox mice showed impaired antibody responses to both T cell-independent and T cell-dependent (TD) antigens, the TD antigen response was markedly impaired as demonstrated by reduced isotype switching, reduced germinal center formation and reduced V region somatic hypermutation. These results show that alpha 4 plays a pivotal role in antigen-specific signal transduction during B cell activation and differentiation in vivo.

Expression of the splice variants of the p85alpha regulatory subunit of phosphoinositide 3-kinase in muscle and adipose tissue of healthy subjects and type 2 diabetic patients

The regulation by insulin of the expression of the p85alpha regulatory subunit of phosphoinositide 3-kinase (PI 3-kinase) is impaired in skeletal muscle and adipose tissue of type 2 diabetic patients. The gene encoding p85alpha (named grb-1) can generate several variants by alternative splicing, all being able to activate the p110 catalytic subunits of PI 3-kinase. Our aims were (i) to determine the mRNA expression profiles of these variants in human skeletal muscle and adipose tissue; (ii) to investigate the effect of insulin on their expression in vivo and in vitro in muscle and (iii) to verify whether this regulation is defective in type 2 diabetes. We determined the human genomic organization of grb-1 and set up reverse transcriptase competitive PCR assays for the quantification of each mRNA variant. In muscle, p85alpha and p50alpha mRNAs were the most abundant, and p55alpha represented less than 20% of all grb-1-derived mRNAs. In adipose tissue, p85alpha was expressed predominantly and p55alpha mRNA was not detectable. These expression profiles were not different in type 2 diabetics. During a 3 h hyperinsulinaemic clamp, insulin increased the mRNA expression of the three variants in muscle of control subjects. In diabetic patients, the effect of insulin on p85alpha and p50alpha mRNAs was blunted, and largely reduced on p55alpha transcripts. In cultured human myotubes, up-regulation of p85alpha, p55alpha and p50alpha mRNAs by insulin was abolished by LY294002 (10 microM) and by rapamycin (50 nM), suggesting that the PI 3-kinase/protein kinase B/p70 S6 kinase pathway could be involved in the stimulation of grb-1 gene expression by insulin in human muscle cells.

Antigen-receptor cross-linking and lipopolysaccharide trigger distinct phosphoinositide 3-kinase-dependent pathways to NF-kappa B activation in primary B cells

The NF-kappaB/Rel transcription factors play an important role in the expression of genes involved in B cell development, differentiation and function. Nuclear NF-kappaB is induced in B cells by engagement of either the BCR or CD40 or by stimulation with lipopolysaccharide (LPS). Despite the importance of NF-kappaB to B cell function, little is known about the signaling pathways leading to NF-kappaB activation. In this report we address the role of phosphoinositide 3'-kinase (PI 3-kinase) in BCR- and LPS-induced NF-kappaB activation using populations of primary murine resting B cells. Using the specific pharmacological inhibitors of PI 3-kinase, Wortmannin and LY294002, we demonstrate that PI 3-kinase activity is vital for BCR-induced NF-kappaB DNA-binding activity. Furthermore, we show that this is achieved via protein kinase C-dependent degradation of IkappaBalpha. Similar analyses reveal that PI 3-kinase is also critical in triggering NF-kappaB DNA-binding activity and IkappaBalpha degradation following LPS stimulation. Interestingly, a PKC inhibitor which blocked the BCR-induced IkappaBalpha degradation had no effect on the degradation of IkappaBalpha after LPS stimulation. Taken together, our results indicate the involvement of PI 3-kinase in at least two distinct signaling pathways leading to activation of NF-kappaB in B cells.

B cell development and activation defects resulting in xid-like immunodeficiency in BLNK/SLP-65-deficient mice

Engagement of the B cell receptor (BCR) leads to the activation of tyrosine kinases and other signaling molecules that ultimately determine the type and magnitude of the B lymphocyte's cellular response. The adaptor protein BLNK/SLP-65 plays a pivotal role in BCR signal transduction by coupling Syk activation to downstream elements such as Grb2, phospholipase C-gamma, Vav and Nck. We have generated BLNK(-/-) mice to determine the physiological role of this protein in B cell development and activation. BLNK(-/-) mice exhibit an incomplete block in B cell development with a severe inhibition of pro-B to pre-B cell differentiation. BLNK(-/-) sIgM(+) cells can develop, seed the peripheral lymphoid tissues and accumulate in numbers overtime. However, these mutant B cells failed to mature and are non-responsive to BCR cross-linking in terms of proliferation and up-regulation of activation markers such as CD69 and CD86 (B7-2). In addition, the CD5(+) subset of B cells is absent. The immune response to T cell-independent antigen but not T cell-dependent antigen is also impaired. Overall, the phenotype of BLNK(-/-) mice bears a striking resemblance to that of xid mice which is the murine model of human XLA that has a mutation in Bruton's tyrosine kinase. This raises the interesting possibility that mutation in BLNK/SLP-65 may be responsible for certain human immunodeficiencies.

Janus kinase 3 (Jak3) is essential for common cytokine receptor gamma chain (gamma(c))-dependent signaling: comparative analysis of gamma(c), Jak3, and gamma(c) and Jak3 double-deficient mice

The common cytokine receptor gamma chain (gamma(c)) is an essential receptor component for IL-2, IL-4, IL-7, IL-9 and IL-15, and thereby gamma(c)-deficient mice exhibit impaired T cell and B cell development. The Janus family tyrosine kinase 3 (Jak3) is known to be associated with gamma(c), and the reported phenotypes of gamma(c)-deficient (gamma(c)(-)) and Jak3-deficient (Jak3(-)) mice are similar, indicating that Jak3 is an essential transducer of gamma(c)-dependent signals. Nevertheless, certain differences have been suggested related to the range of actions of gamma(c) and Jak3. To clarify whether gamma(c)-dependent cytokines can partially transduce their signals without Jak3, we compared lymphocyte development in gamma(c)(-), Jak3(-), and gamma(c) and Jak3 double-deficient (gamma(c)(-)Jak3(-)) mice in the same genetic background. With the exception that T and B cells in Jak3(-) mice express high levels of gamma(c), the defects in thymocyte and peripheral T cell and B cell development are indistinguishable among gamma(c)(-), Jak3(-) and gamma(c)(-)Jak3(-) mice. Interestingly, although Bcl-2 induction was previously suggested to be Jak3-independent, IL-7 cannot induce Bcl-2 expression in CD4 single-positive (SP) thymocytes in either gamma(c)(-) or Jak3(-) mice nor can IL-7 rescue CD4 SP thymocytes from dexamethasone-induced cell death in gamma(c)(-) or Jak3(-) mice. These results indicate that Jak3 is absolutely essential for gamma(c)-dependent T cell and B cell development, and for gamma(c)-dependent prevention of thymocyte apoptosis.