Generation and characterization of a monoclonal antibody against canine tissue factor.

Tissue factor (TF, coagulation factor III) has recently identified roles in innate immunity and cancer. We generated a murine mAb against canine TF (cTF) cloned from Madin-Darby canine kidney cells and expressed in Chinese Hamster Ovarian (CHO) cells, with an equine IL-4 tag. One clone was selected for purification based on initial screening of CHO cell supernatants. The mAb was further characterized with flow cytometry, immunofluorescent microscopy, immunoblotting and immunohistochemical staining of normal and neoplastic canine tissue. The mAb labeled high, but not low, TF-expressing canine breast cancer (CMT25) and osteosarcoma (HMPOS) cells with flow cytometry and immunofluorescent microscopy. Immunoblotting revealed a 42kDa protein with homogenized canine brain and CMT25, but not HMPOS, lysates. The mAb labeled renal tubules and glomeruli, intestinal and dermal epithelium, and arteriolar adventitial cells in frozen tissues. Using immunofluorescent microscopy, increased numbers of labeled PBMCs were observed after LPS stimulation. Our results indicate that the anti-cTF mAb detects a protein with the expected tissue distribution and molecular weight of TF in normal, LPS-stimulated and neoplastic canine cells. This mAb may prove useful for exploring the role of TF in neoplastic and infectious disorders in dogs.

Effect of recombinant canine interleukin-6 and interleukin-8 on tissue factor procoagulant activity in canine peripheral blood mononuclear cells and purified canine monocytes.

BACKGROUND: Inflammation is a major cause of disseminated intravascular coagulation (DIC) in dogs, but underlying mechanisms for its initiation are unknown. We hypothesized that pro-inflammatory cytokines, interleukin (IL)-6 and IL-8, induce tissue factor (TF) expression on canine monocyte surfaces, which may contribute to DIC initiation. OBJECTIVES: The objectives of this study were to determine if (1) IL-6 and IL-8 would induce TF activity on canine monocytes, (2) fetal bovine serum or autologous plasma was required for IL-6- or IL-8-induced TF responses in canine monocytes, and (3) these pro-inflammatory cytokines would enhance TF activity on canine monocytes in response to low concentrations of lipopolysaccharide (LPS). METHODS: Canine monocytes were isolated from EDTA-anticoagulated blood as peripheral blood mononuclear cells (PBMC) by double-density gradient centrifugation and adhesion to plastic. Adherent cells were stimulated for 4 hours with recombinant canine (rc)-IL-6 or rc-IL-8 (10-5000 pg/mL) with or without 10% heat-inactivated (HI) fetal bovine serum, untreated autologous canine plasma (ACP), or HI-ACP. Lipopolysaccharide (100 ng/mL) served as a positive control. Cells were also costimulated with either cytokine (100 pg/mL) or low concentrations of LPS (0.1 and 1 ng/mL). Monocytes immunopurified from PBMC with anti-CD14 antibodies were also stimulated with both cytokines (100 and 5000 pg/mL). TF activity on cell surfaces was measured by a 2-stage amidolytic assay, based on activated factor X generation. RESULTS: Neither rc-IL-6 nor rc-IL-8 consistently stimulated TF procoagulant activity in canine PBMC or purified monocytes after 4 hours. Serum, plasma, or low concentrations of LPS did not enhance the TF response to these cytokines. CONCLUSIONS: IL-6 or IL-8 at evaluated concentrations may not play major roles in coagulation activation by induction of TF expression on monocytes in dogs with inflammation.

Evaluation of tissue factor expression in canine tumor cells.

OBJECTIVE: To determine whether canine tumor cell lines express functional tissue factor and shed tissue factor-containing microparticles. SAMPLE: Cell lines derived from tumors of the canine mammary gland (CMT12 and CMT25), pancreas (P404), lung (BACA), prostate gland (Ace-1), bone (HMPOS, D-17, and OS2.4), and soft tissue (A72); from normal canine renal epithelium (MDCK); and from a malignant human mammary tumor (MDA-MB-231). PROCEDURES: Tissue factor mRNA and antigen expression were evaluated in cells by use of canine-specific primers in a reverse transcriptase PCR assay and a rabbit polyclonal anti-human tissue factor antibody in flow cytometric and immunofluorescent microscopic assays, respectively. Tissue factor procoagulant activity on cell surfaces, in whole cell lysates, and in microparticle pellets was measured by use of an activated factor X-dependent chromogenic assay. RESULTS: Canine tissue factor mRNA was identified in all canine tumor cells. All canine tumor cells expressed intracellular tissue factor; however, the HMPOS and D-17 osteosarcoma cells lacked surface tissue factor expression and activity. The highest tissue factor expression and activity were observed in canine mammary tumor cells and pulmonary carcinoma cells (BACA). These 3 tumors also shed tissue factor-bearing microparticles into tissue culture supernatants. CONCLUSIONS AND CLINICAL RELEVANCE: Tissue factor was constitutively highly expressed in canine tumor cell lines, particularly those derived from epithelial tumors. Because tumor-associated tissue factor can promote tumor growth and metastasis in human patients, high tissue factor expression could affect the in vivo biological behavior of these tumors in dogs.

Evaluation of tissue factor procoagulant activity on the surface of feline leukocytes in response to treatment with lipopolysaccharide and heat-inactivated fetal bovine serum.

OBJECTIVE: To use a chromogenic assay to measure tissue factor (TF) activity on the cell surface and in whole cell lysates of feline monocytes in response to treatment with lipopolysaccharide (LPS) and fetal bovine serum (FBS). ANIMALS: 14 healthy cats. PROCEDURES: Peripheral blood monocytes were isolated via density gradient centrifugation followed by adhesion to plastic. Tissue factor procoagulant activity was measured by use of an assay that detects TF-activated factor X, on the basis of cleavage of a chromogenic TF-activated factor X-dependent substrate. Activity was quantified by comparison with a serially diluted human recombinant TF-activated factor x curve. RESULTS: The TF procoagulant activity assay was sensitive and specific for TF. Treatment with LPS stimulated TF procoagulant activity on the surface and in whole cell lysates of isolated feline leukocytes. The LPS response in intact cells was dose dependent and cell number dependent and was inhibited by FBS. Monocyte isolation was inefficient, with monocytes comprising a mean of 22% of the isolated cells. CONCLUSIONS AND CLINICAL RELEVANCE: A TF-activated factor X-dependent chromogenic assay that uses human reagents successfully measured surface-expressed and intracellular TF activity of feline monocytes. Treatment with LPS induced TF expression on feline monocytes, but this response was inhibited by FBS. The chromogenic assay was a useful method for measuring TF procoagulant activity in feline cells in vitro and can be used as a research tool to investigate the role of cell-associated TF in thrombotic disorders in cats.

The Rac1 C-terminal polybasic region regulates the nuclear localization and protein degradation of Rac1.

We observed evolutionary conservation of canonical nuclear localization signal sequences (K(K/R)X(K/R)) in the C-terminal polybasic regions (PBRs) of some Rac and Rho isoforms. Canonical D-box sequences (RXXL), which target proteins for proteasome-mediated degradation, are also evolutionarily conserved near the PBRs of these small GTPases. We show that the Rac1 PBR (PVKKRKRK) promotes Rac1 nuclear accumulation, whereas the RhoA PBR (RRGKKKSG) keeps RhoA in the cytoplasm. A mutant Rac1 protein named Rac1 (pbrRhoA), in which the RhoA PBR replaces the Rac1 PBR, has greater cytoplasmic localization, enhanced resistance to proteasome-mediated degradation, and higher protein levels than Rac1. Mutating the D-box by substituting alanines at amino acids 174 and 177 significantly increases the protein levels of Rac1 but not Rac1(pbrRhoA). These results suggest that Rac1 (pbrRhoA) is more resistant than Rac1 to proteasome-mediated degradative pathways involving the D-box. The cytoplasmic localization of Rac1(pbrRhoA) provides the most obvious reason for its resistance to proteasome-mediated degradation, because we show that Rac1(pbrRhoA) does not greatly differ from Rac1 in its ability to stimulate membrane ruffling or to interact with SmgGDS and IQGAP1-calmodulin complexes. These findings support the model that nuclear localization signal sequences in the PBR direct Rac1 to the nucleus, where Rac1 participates in signaling pathways that ultimately target it for degradation.