The absence of Grb2-associated binder 2 (Gab2) does not disrupt NK cell development and functions

LncRNA NCAL1 potentiates natural killer cell cytotoxicity through the Gab2-PI3K-AKT pathway

Natural killer (NK) cells perform immune surveillance functions in tumors. The antitumor effects of NK cells are closely related to tumor occurrence and development. However, the molecular factors that determine NK cell antitumor activity remain to be characterized. In the present study, we identified a novel long noncoding RNA (lncRNA), NK cell activity-associated lncRNA 1 (NCAL1), and investigated its function in NK cells. NCAL1 was primarily located in NK cell nuclei, where it functioned by activating Gab2, a scaffold protein with an essential role in immune cells. Gab2 positively regulated the killing activity of NK cells. Mechanistically, NCAL1 upregulated Gab2 epigenetically by binding to the Gab2 promoter, which decreased methylation, recruited the transcription factor Sp1, and increased H3K4me3 and H3K27ac levels in the Gab2 promoter. Furthermore, NCAL1 enhanced the cytotoxicity of NK cells toward tumor cells through the Gab2-PI3K-AKT pathway. Thus, NCAL1 potentiates NK cell cytotoxicity and is a promising therapeutic target to improve NK cell therapy.

siRNA-Conjugated Nanoparticles to Treat Ovarian Cancer

Ovarian cancer is the fifth-most lethal cancer among women due to a lack of early detection and late-stage treatment options, and it is responsible for more than 14,000 deaths each year in the United States. Recently, there have been advances in RNA interference therapy, specifically with small interfering RNA (siRNA), to reduce tumor burden for ovarian cancer via gene down-regulation. However, delivery of siRNA poses its own challenges, as siRNA is unstable in circulation, is unable to be effectively internalized by cells, and may cause toxicity in off-target sites. To address such challenges, nanoparticle carriers have emerged as delivery platforms for the biocompatible, targeted delivery of siRNA-based therapies. Several preclinical studies have shown the promising effects of siRNA therapy to reduce chemotherapy resistance and proliferation of ovarian cancer cells. This review evaluates the recent advances, clinical applications, and future potential of nanoparticle-mediated delivery of siRNA therapeutics to target genes implicated in ovarian cancer.

Highly efficient Gab2 siRNA delivery to ovarian cancer cells mediated by chitosan–polyethyleneimine nanoparticles

Malignant bowel obstruction (MBO) is a serious complication which causes high death rate and low quality of life (QOL) for patients diagnosed at an advanced stage of ovarian cancer.

Function, regulation and pathological roles of the Gab/DOS docking proteins

Since their discovery a little more than a decade ago, the docking proteins of the Gab/DOS family have emerged as important signalling elements in metazoans. Gab/DOS proteins integrate and amplify signals from a wide variety of sources including growth factor, cytokine and antigen receptors as well as cell adhesion molecules. They also contribute to signal diversification by channelling the information from activated receptors into signalling pathways with distinct biological functions. Recent approaches in protein biochemistry and systems biology have revealed that Gab proteins are subject to complex regulation by feed-forward and feedback phosphorylation events as well as protein-protein interactions. Thus, Gab/DOS docking proteins are at the centre of entire signalling subsystems and fulfil an important if not essential role in many physiological processes. Furthermore, aberrant signalling by Gab proteins has been increasingly linked to human diseases from various forms of neoplasia to Alzheimer's disease.

In this review, we provide a detailed overview of the structure, effector functions, regulation and evolution of the Gab/DOS family. We also summarize recent findings implicating Gab proteins, in particular the Gab2 isoform, in leukaemia, solid tumours and other human diseases.

The GAB2 gene and the risk of Alzheimer's disease: replication and meta-analysis

BACKGROUND

Recently, GAB2 has been suggested to modify the risk of late-onset Alzheimer's disease (AD) among APOEepsilon4 carriers. However, replication data are inconsistent.

METHODS

In a population-based cohort study (n = 5507; age > 55) with 443 incident AD cases, we investigated the association between rs4945261 and AD. Because we used high-density genotyping, we also investigated other polymorphisms within and around GAB2 and performed a meta-analysis with published studies.

RESULTS

We found that rs4945261 was associated with AD among APOEepsilon4 carriers (p = .02) but not among noncarriers (p = .26). Fifteen of the 20 remaining polymorphisms within GAB2 and several polymorphisms in the 250kbp-region surrounding GAB2 were also associated with AD among carriers and only one among noncarriers. For rs2373115, meta-analysis yielded an odds ratio of 1.58 (1.17-2.14) with p = 3.0 * 10(-3) among carriers and 1.09 (.97-1.23) with p = .16 among noncarriers. For rs4945261, the pooled odds ratio was 1.75 (1.21-2.55) with p = 3.0 * 10(-3) among carriers and 1.20 (1.01-1.41) with p = .03 among noncarriers.

CONCLUSIONS

We found GAB2 to be associated with AD. Furthermore, the meta-analysis also suggests that GAB2 modifies the risk of AD in APOEepsilon4 carriers.

Grb2 associated binder 2 couples B-cell receptor to cell survival

B-cell fate during maturation and the germinal center reaction is regulated through the strength and the duration of the B-cell receptor signal. Signaling pathways discriminating between apoptosis and survival in B cells are keys in understanding adaptive immunity. Gab2 is a member of the Gab/Dos adaptor protein family. It has been shown in several model systems that Gab/Dos family members may regulate both the anti-apoptotic PI3-K/Akt and the mitogenic Ras/MAPK pathways, still their role in B-cells have not been investigated in detail. Here we studied the role of Gab2 in B-cell receptor mediated signaling. We have shown that BCR crosslinking induces the marked phosphorylation of Gab2 through both Lyn and Syk kinases. Subsequently Gab2 recruits p85 regulatory subunit of PI3-K, and SHP-2. Our results revealed that Ig-alpha/Ig-beta, signal transducing unit of the B-cell receptor, may function as scaffold recruiting Gab2 to the signalosome. Overexpression of Gab2 in A20 cells demonstrated that Gab2 is a regulator of the PI3-K/Akt but not that of the Ras/MAPK pathway in B cells. Accordingly to the elevated Akt phosphorylation, overexpression of wild-type Gab2 in A20 cells suppressed Fas-mediated apoptosis, and enhanced BCR-mediated rescue from Fas-induced cell death. Although PH-domain has only a stabilizing effect on membrane recruitment of Gab2, it is indispensable in mediating its anti-apoptotic effect.

The p110delta catalytic isoform of PI3K is a key player in NK-cell development and cytokine secretion

The signal transduction pathways that lead activated natural killer (NK) cells to produce cytokines, releases cytotoxic granules, or do both, are not clearly dissected. For example, phosphoinositide 3-kinases (PI3Ks) are key players in the execution of both functions, but the relative contribution of each isoform is unknown. We show here that the catalytic isoform p110δ, not p110γ, was required for interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), and granulocyte macrophage colony-stimulating factor (GM-CSF) secretion, whereas neither was necessary for cytotoxicity. Yet, when both p110δ and p110γ isoforms were inactivated by a combination of genetic and biochemical approaches, cytotoxicity was decreased. NK-cell numbers were also affected by the lack of p110δ but not p110γ and more severely so in mice lacking both subunits. These results provide genetic evidence that p110δ is the dominant PI3K isoform for cytokine secretion by NK cells and suggest that PI3Ks cooperate during NK-cell development and cytotoxicity.

GAB2 alleles modify Alzheimer's risk in APOE epsilon4 carriers

The apolipoprotein E (APOE) epsilon4 allele is the best established genetic risk factor for late-onset Alzheimer's disease (LOAD). We conducted genome-wide surveys of 502,627 single-nucleotide polymorphisms (SNPs) to characterize and confirm other LOAD susceptibility genes. In epsilon4 carriers from neuropathologically verified discovery, neuropathologically verified replication, and clinically characterized replication cohorts of 1411 cases and controls, LOAD was associated with six SNPs from the GRB-associated binding protein 2 (GAB2) gene and a common haplotype encompassing the entire GAB2 gene. SNP rs2373115 (p = 9 x 10(-11)) was associated with an odds ratio of 4.06 (confidence interval 2.81-14.69), which interacts with APOE epsilon4 to further modify risk. GAB2 was overexpressed in pathologically vulnerable neurons; the Gab2 protein was detected in neurons, tangle-bearing neurons, and dystrophic neuritis; and interference with GAB2 gene expression increased tau phosphorylation. Our findings suggest that GAB2 modifies LOAD risk in APOE epsilon4 carriers and influences Alzheimer's neuropathology.

Gab2 requires membrane targeting and the met binding motif to promote lamellipodia, cell scatter, and epithelial morphogenesis downstream from the met receptor

Gab1 and Gab2 are conserved scaffolding proteins that amplify and integrate signals stimulated by many growth factor receptors including the Met receptor. Gab1 acts to diversify the signal downstream from Met through the recruitment of multiple signaling proteins, and is essential for epithelial morphogenesis. However, whereas Gab1 and Gab2 are both expressed in epithelial cells, Gab2 fails to support a morphogenic response. We demonstrate that Gab1 and Gab2 are divergent in their function whereby Gab1, but not Gab2, promotes lamellipodia formation, and is localized to the membrane of lamellipodia upon Met activation. We have identified activation of ERK1/2 as a requirement for lamellipodia formation. Moreover, activated ERK1/2 are localized to lamellipodia in Gab1 expressing cells but not in cells that overexpress Gab2. By structure-function studies, we identify that enhanced membrane localization conferred through the addition of a myristoylation signal, together with the addition of the direct Met binding motif (MBM) from Gab1, are required to promote lamellipodia and confer a morphogenic signaling response to Gab2. Moreover, the morphogenesis competent myristoylated Gab2MBM promotes localization of activated ERK1/2 to the leading edge of lamellipodia in a similar manner to Gab1. Hence, subcellular localization of the Gab scaffold, as well as the ability of Gab to interact directly with the Met receptor, are both essential components of the morphogenic signaling response which involves lamellipodia formation and the localization of ERK1/2 activation in membrane ruffles.

Strategies of natural killer cell recognition and signaling

The participation of natural killer (NK) cells in multiple aspects of innate and adaptive immune responses is supported by the wide array of stimulatory and inhibitory receptors they bear. Here we review the receptor-ligand interactions and subsequent signaling events that culminate in NK effector responses. Whereas some receptor-ligand interactions result in activation of both NK cytotoxicity and cytokine production, others have more subtle effects, selectively activating only one pathway or having distinct context-dependent effects. Recent approaches offer ways to unravel how the integration of complex signaling networks directs the NK response.

Anatomy of a murder—signal transduction pathways leading to activation of natural killer cells

Natural killer (NK) cells control the early phases of viral infections, modulate antigen-specific immune responses, and participate in the rejection of tumours and bone marrow grafts. A fine balance between inhibitory and activating receptors tightly regulates NK cell activation. Biochemical studies in human cell lines and primary cells have revealed some of the activating NK cell signalling pathways, however animal models are instrumental to understand the physiological implications of these findings for immune responses in vivo. Gene targeting in mice and biochemical studies in cells are helping to dissect out the various signal transduction pathways that control NK cell activation. A clearer view of these pathways may eventually help designing more effective immune therapies based on the use of NK cells.