Activation of c-Jun N-terminal kinase in the absence of NFkappaB function prior to induction of NK cell death triggered by a combination of anti-class I and anti-CD16 antibodies

Reverse Signaling by MHC-I Molecules in Immune and Non-Immune Cell Types

Major histocompatibility complex (MHC) molecules are well-known for their role in antigen (cross-) presentation, thereby functioning as key players in the communication between immune cells, for example dendritic cells (DCs) and T cells, or immune cells and their targets, such as T cells and virus-infected or tumor cells. However, much less appreciated is the fact that MHC molecules can also act as signaling receptors. In this process, here referred to as reverse MHC class I (MHC-I) signaling, ligation of MHC molecules can lead to signal-transduction and cell regulatory effects in the antigen presenting cell. In the case of MHC-I, reverse signaling can have several outcomes, including apoptosis, migration, induced or reduced proliferation and cytotoxicity towards target cells. Here, we provide an overview of studies showing the signaling pathways and cell outcomes upon MHC-I stimulation in various immune and non-immune cells. Signaling molecules like RAC-alpha serine/threonine-protein kinase (Akt1), extracellular signal-regulated kinases 1/2 (ERK1/2), and nuclear factor-κB (NF-κB) were common signaling molecules activated upon MHC-I ligation in multiple cell types. For endothelial and smooth muscle cells, the in vivo relevance of reverse MHC-I signaling has been established, namely in the context of adverse effects after tissue transplantation. For other cell types, the role of reverse MHC-I signaling is less clear, since aspects like the in vivo relevance, natural MHC-I ligands and the extended downstream pathways are not fully known.The existing evidence, however, suggests that reverse MHC-I signaling is involved in the regulation of the defense against bacterial and viral infections and against malignancies. Thereby, reverse MHC-I signaling is a potential target for therapies against viral and bacterial infections, cancer immunotherapies and management of organ transplantation outcomes.

Differentiation by NK cells is a prerequisite for effective targeting of cancer stem cells/poorly differentiated tumors by chemopreventive and chemotherapeutic drugs

Natural Killer (NK) cells target oral, pancreatic, lung, breast, glioblastoma and melanoma stem-like/poorly differentiated tumors. Differentiation of the abovementioned tumors with supernatants from split-anergized NK cells decreases their susceptibility to NK cells, but increases their sensitivity to cisplatin (CDDP)-mediated cell death. Breast and melanoma tumor cells with CD44 knockdown display enhanced susceptibility to NK cell-mediated lysis, potentially due to decreased differentiation. We also demonstrate that sulindac, a non-steroidal anti-inflammatory drug and a chemopreventive agent, not only limits the growth of oral tumor cells, but also aids in cancer cell elimination by NK cells. Treatment of oral tumors with sulindac, but not adriamycin inversely modulates the expression and function of NFκB and JNK, resulting in a significant down-regulation of IL-6, and VEGF secretion by oral tumor cells. In addition, increased secretion of IL-6 and VEGF is blocked by sulindac during interaction of oral tumors with NK cells. Sulindac treatment prevents synergistic induction of VEGF secretion by the tumor cells after their co-culture with untreated NK cells since non-activated NK cells lack the ability to efficiently kill tumor cells. Moreover, sulindac is able to profoundly reduce VEGF secretion by tumor cells cultured with IL-2 activated NK cells, which are able to significantly lyse the tumor cells. Based on the data presented in this study, we propose the following combinatorial approach for the treatment of stem-like/ poorly differentiated tumors in cancer patients with metastatic disease. Stem-like/ poorly differentiated tumor cells may in part undergo lysis or differentiation after NK cell immunotherapy, followed by treatment of differentiated tumors with chemotherapy and chemopreventive agents to eliminate the bulk of the tumor. This dual approach should limit tumor growth and prevent metastasis.

N-acetyl cysteine mediates protection from 2-hydroxyethyl methacrylate induced apoptosis via nuclear factor kappa B-dependent and independent pathways: potential involvement of JNK

The mechanisms by which resin based materials induce adverse effects in patients have not been completely elucidated. Here we show that 2-hydroxyethyl methacrylate (HEMA) induces apoptotic cell death in oral keratinocytes. Functional loss and cell death induced by HEMA was significantly inhibited in the presence of N-acetyl cysteine (NAC) treatment. NAC also prevented HEMA mediated decrease in vascular endothelial growth factor secretion. The protective effect of NAC was partly related to its ability to induce NF-kappaB in the cells, since HEMA mediated inhibition of nuclear NF-kappaB expression and function was significantly blocked in the presence of NAC treatment. Moreover, blocking of nuclear translocation of NF-kappaB in oral keratinocytes sensitized these cells to HEMA mediated apoptosis. In addition, since NAC was capable of rescuing close to 50% of NF-kappaB knockdown cells from HEMA mediated cell death, there is, therefore, an NF-kappaB independent pathway of protection from HEMA mediated cell death by NAC. NAC mediated prevention of HEMA induced cell death in NF-kappaB knockdown cells was correlated with a decreased induction of c-Jun N-terminal kinase (JNK) activity since NAC inhibited HEMA mediated increase in JNK levels. Furthermore, the addition of a pharmacologic JNK inhibitor to HEMA treated cells prevented cell death and restored NF-kappaB knockdown cell function significantly. Therefore, NAC protects oral keratinocytes from the toxic effects of HEMA through NF-kappaB dependent and independent pathways. Moreover, our data suggest the potential involvement of JNK pathway in NAC mediated protection.

Regulation of IGFBP6 gene and protein is mediated by the inverse expression and function of c-jun N-terminal kinase (JNK) and NFkappaB in a model of oral tumor cells

The aim of this study is to identify potential gene and protein targets when nuclear factor kappa B (NFkappaB) and c-jun N-terminal kinase (JNK) were inversely expressed in oral tumors. To determine which genes were regulated synergistically by the inverse expression of NFkappaB and JNK, a pathway specific microarray analysis was performed. While either inhibition of NFkappaB or activation of JNK alone was unable to affect the IGFBP6 gene expression in microarray analysis, concomitant increase in JNK activation in the presence of NFkappaB inhibition increased the expression of this gene significantly. Synergistic increase in IGFBP6 gene expression was also confirmed by RT-PCR and Northern blot analysis of transfected cells. Accordingly, the levels of IGFBP6 protein secretion rose synergistically when JNK was over-expressed in NFkappaB knock down cells. In addition, increased expression of JNK in the absence of NFkappaB resulted in a significant induction of cell death in oral tumors when either left untreated or treated with TNF-alpha and TPA. Moreover, when JNK was inhibited by dominant negative JNK (APF), a significant decrease in cell death could be observed in TNF-alpha and TPA treated NFkappaB knock down oral tumors. Therefore, increased induction of IGFBP6 gene or protein expression in oral tumors could be regarded as a potential predictive marker of tumor sensitivity and could be used for prognostic purposes, since a significant correlation could be observed between increased induction of apoptotic cell death and elevated levels of IGFBP6 in these tumors.

Rapid and potent induction of cell death and loss of NK cell cytotoxicity against oral tumors by F(ab')2 fragment of anti-CD16 antibody

Freshly isolated untreated NK cells undergo rapid apoptosis and lose their cytotoxic function upon the addition of F(ab')2 fragment of anti-CD16 antibodies. Loss of NK cell cytotoxic function after treatment with F(ab')2 fragment of anti-CD16 antibody can be seen against K562 and UCLA-2 oral tumor cells when either added immediately in the co-cultures of NK cells with the tumor cells or after pre-treatment of NK cells with the antibody before their addition to the tumor cells. Addition of Interleukin-2 (IL-2) in combination with anti-CD16 antibody to NK cells delayed the induction of DNA fragmentation in NK cells, and even though decreased cytotoxicity could still be observed against K562 and UCLA-2 oral tumors when compared to IL-2 alone treated NK cells, the cytotoxicity levels remained relatively higher and approached those obtained by untreated NK cells in the absence of antibody treatment. No increases in IFN-gamma, Granzymes A and B, Perforin and TRAIL genes could be seen in NK cells treated with anti-CD16 antibody. Neither secretion of IFN-gamma nor increased expression of CD69 activation antigen could be observed after the treatment of NK cells with anti-CD16 antibody. Furthermore, IL-2 mediated increase in CD69 surface antigens was down-modulated by anti-CD16 antibody. Finally, the addition of anti-CD16 antibody to co-cultures of NK cells with tumor target cells was not inhibitory for the secretion of VEGF by oral tumor cells, unlike those co-cultured with untreated or IL-2 treated NK cells. Thus, binding and triggering of CD16 receptor on NK cells may enhance oral tumor survival and growth by decreased ability of NK cells to suppress VEGF secretion or induce tumor cell death during the interaction of NK cells with oral tumor cells.

NKp30 ligation induces rapid activation of the canonical NF-kappaB pathway in NK cells

Studies of patients with congenital immunodeficiency due to mutation of the NF-kappaB essential modulator (NEMO) gene have demonstrated that NEMO integrity is required for NK cell cytotoxicity. Thus, we have studied the physiology of NF-kappaB activation in NK cells during the cytolytic program. In resting ex vivo human NK cells or cell lines, IkappaB was degraded after 10 min exposure to PMA and ionomycin, or TNF and was maximally degraded by 30 min. Ligation of several NK cell activation receptors including NKp30 induced a similar response and was blocked by pretreatment with the proteosome inhibitor MG132. There was no short-term effect on p100 processing, the signature of noncanonical NF-kappaB activation. NK cell IkappaB degradation corresponded to increases in nuclear NF-kappaB as detected by EMSA. Supershift of stimulated NK cells and fluorescence microscopy of individual NK cells in cytolytic conjugates demonstrated that the p65/p50 heterodimer was the primary NF-kappaB used. NF-kappaB function was evaluated in NK92 cells transduced with a kappaB GFP reporter, and their conjugation with K562 cells or ligation of NKp30 ligation resulted in rapid GFP accumulation. The latter was prevented by the Syk inhibitor piceatannol. Thus, NK cell activation signaling specifically induces transcriptional activation and synthesis of new NF-kappaB dependent proteins during the initiation of cytotoxicity.

Coengagement of CD16 and CD94 receptors mediates secretion of chemokines and induces apoptotic death of naive natural killer cells

Down-modulation of CD16 (FcgammaRIII) receptors and loss of natural killer (NK) cell function have been observed in oral cancer patients. However, neither the mechanisms nor the significance of the decrease in CD16 receptors have been fully understood. The cytotoxic activity and survival of NK cells are negatively regulated by antibodies directed against CD16 surface receptor. The addition of anti-CD94 antibody in combination with either F(ab')(2) fragment or intact anti-CD16 antibody to NK cells resulted in significant inhibition of NK cell cytotoxic function and induction of apoptosis in resting human peripheral blood NK cells. Addition of interleukin-2 to anti-CD16 and/or anti-CD94 antibody-treated NK cells significantly inhibited apoptosis and increased the function of NK cells. There was a significant increase in tumor necrosis factor-alpha (TNF-alpha) but not IFN-gamma secretion in NK cells treated either with anti-CD16 antibody alone or in combination with anti-CD94 antibodies. Consequently, the addition of anti-TNF-alpha antibody partially inhibited apoptosis of NK cells mediated by the combination of anti-CD94 and anti-CD16 antibodies. Increase in apoptotic death of NK cells also correlated with an increase in type 2 inflammatory cytokines and in the induction of chemokines. Thus, we conclude that binding of antibodies to CD16 and CD94 NK cell receptors induces death of the NK cells and signals for the release of chemokines.