Characterization of baboon NK cells and their xenogeneic activity.

BACKGROUND: Baboons are commonly used as models for transplantation and preclinical testing of various types of therapeutic agents. For proper assessment of information gathered from these models, differences between the baboon and human immune systems need to be characterized. Natural killer (NK) cells are the first line of defense against many infectious agents and cancer and are important mediators of transplantation rejection reactions, particularly during xenotransplantation. In this study, we examined baboon NK cell function and developed methods for purifying and expanding these cells. METHODS: Baboon NK cells were analyzed using a combination of extracellular and intracellular cell staining, cell sorting, interleukin (IL)-2 mediated stimulation and expansion, and 4 h cytotoxicity assays with human and pig target cell lines. RESULTS: Baboon peripheral blood mononuclear cell (PBMC) exert very low but detectable cytolytic activity against both human (K562) and pig (PAEC, J2) target cells, and this activity is enhanced within 4 h of treatment with IL-2. Like human NK cells, many baboon PBMC express the lytic enzymes granzyme A, granzyme B, and perforin. Based on these markers, we identified a subpopulation of CD3(-) baboon lymphocytes that are CD8(dim) and CD16(bright) that likely represents the baboon NK cells. These cells also are characterized by expression of the natural cytotoxicity receptor NKp46. Baboon CD3(-)NKp46(+) cells purified by flow cytometric cell sorting have high cytolytic capacity that can be further enhanced by IL-2 stimulation. These baboon NK cells can be expanded in vitro and retain extremely high cytolytic capacity. While fresh baboon lymphocytes express very little CD56, the expanded baboon NK cells are predominantly CD56(+); approximately 10% of the expanded NK cells are CD56(dim), and the remainder are CD56(bright). CONCLUSIONS: Baboon NK cells that are IL-2 responsive can be identified on the basis of a CD3(-)NKp46(+)CD8(dim)CD16(+/-) or CD3(-)CD8(dim)CD16(bright) phenotype and can be isolated and expanded in culture. These results may allow for a more accurate representation of the human innate immune system in baboon models and more accurate analyses of the role of the baboon innate immune system cells in preclinical models.

Osmotic stress-dependent repression is mediated by histone H3 phosphorylation and chromatin structure.

Histone H3 phosphorylation has been linked to various environmental stress responses and specific chromatin structure. The role of H3 phosphorylation in the osmotic stress response was investigated on the mouse mammary tumor virus (MMTV) promoter in different chromatin configurations. Hormone-dependent transcription from the MMTV promoter is repressed by osmotic stress when the promoter is integrated and has a normal chromatin structure. However, when the MMTV promoter is transiently transfected, the chromatin structure is less organized, and hormone induction is not affected by osmotic stress. On the integrated MMTV promoter, phosphorylation of histone H3 serine 10 and 28 increases in response to osmotic stress, but the transient promoter shows no change. Hormone-dependent glucocorticoid receptor binding is reduced on the repressed promoter, and elevated H3 phosphorylation is temporally correlated with maximal MMTV repression Additionally, the protein kinase C inhibitor rottlerin, but not other kinase inhibitors, blocks both histone H3 phosphorylation and osmotic repression of MMTV transcription. Glucocorticoid receptor binding is inversely correlated with H3 phosphorylation, suggesting that displacement of the glucocorticoid receptor from the promoter is due to H3 phosphorylation and is the mechanism for the osmotic repression of hormone-dependent transcription.

15S-Lipoxygenase-2 mediates arachidonic acid-stimulated adhesion of human breast carcinoma cells through the activation of TAK1, MKK6, and p38 MAPK.

The dietary cis-polyunsaturated fatty acid, arachidonic acid, stimulates adhesion of metastatic human breast carcinoma cells (MDA-MB-435) to the extracellular matrix, but the molecular mechanisms by which fatty acids modify the behavior of these cells are unclear. Exposure to arachidonic acid activates multiple signaling pathways. Activation of p38 mitogen-activated protein kinase (p38 MAPK) is required for increased cell adhesion to type IV collagen, and this activation is sensitive to inhibitors of lipoxygenases, suggesting a requirement for arachidonic acid metabolism. The goals of the current study were to identify the one or more key metabolites of arachidonic acid that are responsible for activation of p38 MAPK and to elucidate the upstream kinases that lead to p38 MAPK activation. High performance liquid chromatographic analysis revealed that MDA-MB-435 cells metabolize exogenous arachidonic acid predominantly to 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE). Immunoblot analysis with antibodies specific to 15(S)-lipoxygenase-1 (LOX-1) and 15(S)-lipoxygenase-2 (LOX-2) demonstrated the expression of 15-LOX-2, but not 15-LOX-1, in these tumor cells. A LOX inhibitor, nordihydroguaiaretic acid, attenuated production of 15(S)-HETE and inhibited the phosphorylation of p38 MAPK following exposure to arachidonic acid. In contrast, overexpression of LOX-2 sensitized the cells to the addition of arachidonic acid, leading to increased activation of p38 MAPK. Addition of exogenous 15(S)-HETE to MDA-MB-435 cells stimulated cell adhesion to type IV collagen and activated the p38 MAPK pathway, including the upstream kinases transforming growth factor-beta1-activated protein kinase-1 (TAK1) and MAPK kinase 6. Transfection of these cells with a dominant negative form of TAK1 blocked arachidonic acid-stimulated p38 MAPK phosphorylation. These data demonstrate that 15(S)-LOX-2 generation of 15(S)-HETE activates specific growth factor receptor-related signaling pathways, thereby initiating signal transduction events leading to increased cell adhesion to the extracellular matrix.

Sumoylation of internally initiated Sp3 isoforms regulates transcriptional repression via a Trichostatin A-insensitive mechanism.

Sp3 is a ubiquitously expressed member of the Sp family of transcription factors that encodes three proteins, Sp3, M1 and M2, with differing capacities to stimulate or repress transcription. As part of ongoing efforts to study the functions of Sp3 isoforms, we employed a yeast "two-hybrid" screen to identify Sp3-binding proteins. This screen resulted in the identification of Ubc9, a SUMO-1 conjugating enzyme, as an M2-binding protein, and consistent with these results sequence analyses identified consensus sumoylation motifs within several Sp family members. Western blots probed with anti-Sp3 detected a high molecular weight Sp3 isoform that is stabilized by a SUMO-1 hydrolase inhibitor, and this protein is also bound by anti-SUMO-1 antiserum. Transient transfection assays with epitope-tagged-SUMO-1 and GFP-SUMO-1 fusion proteins confirmed that Sp3, M1 and M2 proteins are sumoylated in vivo. Substitution of arginine for lysine at one putative site of sumoylation, lysine(551), blocked sumoylation of all Sp3 isoforms in vivo and led to a marginal increase in Sp3-mediated trans-activation in insect and mammalian cells. In contrast, introduction of this amino acid substitution within M1 converted it into a potent transcriptional trans-activator. We conclude that Sp3 isoforms are sumoylated in vivo and this post-translational modification plays an important role in the regulation of Sp3-mediated transcription.

Requirement of protein kinase C micro activation and calpain-mediated proteolysis for arachidonic acid-stimulated adhesion of MDA-MB-435 human mammary carcinoma cells to collagen type IV.

Arachidonic acid (AA) stimulation of adhesion of human metastatic breast carcinoma cells to collagen type IV depends on the protein kinase C (PKC) pathway(s) and is associated with the translocation of PKC mu from the cytoplasm to the membrane. In the present study, we have further explored the role of PKC mu in AA-stimulated adhesion. PKC mu activation site serines 738/742 and autophosphorylation site serine 910 are rapidly phosphorylated, and in vitro PKC mu kinase activity is enhanced in response to AA treatment. Inhibition of PKC mu activation blocks AA-stimulated adhesion. A phosphorylated, truncated species of PKC mu was detected in AA-treated cells. This 77-kDa protein contains the kinase domain but lacks a significant portion of the regulatory domains. Inhibition of calpain protease activity blocks generation of the truncated protein, promotes accumulation of the activated, full-length protein in the membrane, and blocks the AA-mediated increase in adhesion. p38 MAPK activity is also required for AA-stimulated adhesion. Activation of PKC mu and p38 are independent events. However, inhibition of p38 activity reduces calpain-mediated proteolysis of PKC mu and in vivo calpain activity, suggesting a role for p38 in regulation of calpain activity and a point for cross-talk between the PKC and MAPK pathways. These results support the hypothesis that AA stimulates activation of PKC mu, which is cleaved by calpain at the cell membrane. The resulting truncated kinase, as well as the full-length kinase, may be required for increased cell adhesion to collagen type IV. Additionally, these studies present the first evidence for calpain cleavage of a non-structural protein leading to the promotion of tumor cell adhesion.

Sp3 represses gene expression via the titration of promoter-specific transcription factors.

We have determined previously that Sp3 encodes three distinct gene products as follows: a full-length protein (Sp3) that is an activator of transcription and two isoforms (M1 and M2) derived via internal translational initiation that function as transcriptional repressors. To identify amino acids and functions required for transcriptional repression, we employed PCR-directed mutagenesis to create a panel of mutated M2 proteins. Biochemical and functional analyses of these mutated proteins indicate that functions encoded by the M2 carboxyl terminus, such as DNA binding activity and the capacity to form multimeric complexes, are not required or sufficient for transcriptional repression. Instead, a 93-amino acid portion of the trans-activation domain was shown to be the minimal portion of M2 required to block Sp-dependent gene expression. Transcriptional analysis of three Sp-dependent promoters showed that mutations sustained by many M2 proteins result in promoter-specific effects. Regions of M2 required for physical interactions with five TATA box-associated factors (TAF(II)s) were mapped, and mutations that disrupt the interaction of M2 with two of these proteins, TAF(II)70 and TAF(II)40, were identified. We conclude that Sp3- mediated transcriptional repression is due, at least in part, to competition for promoter-specific transcription factors.