cDNA microarray gene expression profiling of hydroxyurea, paclitaxel, and p-anisidine, genotoxic compounds with differing tumorigenicity results

The potential application of toxicogenomics to predictive toxicology has been discussed widely, but the utility of the approach remains largely unproven. Using cDNA microarrays, we compared the gene expression profiles produced in mouse lymphoma cells by three genotoxic compounds, hydroxyurea (a carcinogen), p-anisidine (a noncarcinogen), and paclitaxel (carcinogenicity unknown). To minimize the effect of biological variability and technological limitations, quadruplicate observations were made for each compound and a subset of genes yielding reproducible induction/repression was selected for comparison. A method was applied to attach normalized expression data to genes with a low false-discovery rate (<0.1) to yield more confidence regarding differential expression. This analysis identified genotoxicity-specific gene expression. Seven genes were consistently upregulated and 12 downregulated more than 2-fold by the three genotoxic compounds. Using additional genes, the expression pattern induced by the genotoxic noncarcinogen, p-anisidine, was readily distinguished from that associated with the genotoxic carcinogen, hydroxyurea. Comparison of paclitaxel-induced expression data to data for p-anisidine and hydroxyurea suggested that paclitaxel's profile is more similar to the genotoxic noncarcinogen. With further supporting evidence it may be possible to perform large-scale monitoring of gene expression during drug and chemical development that can provide an early warning of potential toxicological responses.

The NKR-P1B Gene Product Is an Inhibitory Receptor on SJL/J NK Cells

The mouse NKR-P1 family includes at least three genes: NKR-P1A, -B, -C. Neither surface expression nor function of the NKR-P1B gene product has previously been shown. Here, we demonstrate that the SJL/J allele of the NKR-P1B gene product is expressed on SJL/J NK cells, and is recognized by PK136 mAb. Interestingly, the same mAb does not recognize the NKR-P1B gene product of C57BL/6. We have also generated a novel mAb, 1C10, that recognizes an activation receptor on SJL/J NK cells. Activation of the NKR-P1B receptor-inhibited 1C10 mAb induced redirected lysis and recruited SHP-1, indicating that NKR-P1B is an inhibitory receptor. Therefore, the mouse NKR-P1 gene family, like the Ly49 family, includes both activation and inhibitory receptors.

Mouse NKR-P1B, a Novel NK1.1 Antigen with Inhibitory Function

The mouse NK1.1 Ag originally defined as NK cell receptor (NKR)-P1C (CD161) mediates NK cell activation. Here, we show that another member of the mouse CD161 family, NKR-P1B, represents a novel NK1.1 Ag. In contrast to NKR-P1C, which functions as an activating receptor, NKR-P1B inhibits NK cell activation. Association of NKR-P1B with Src homology 2-containing protein tyrosine phosphatase-1 provides a molecular mechanism for this inhibition. The existence of these two NK1.1 Ags with opposite functions suggests a potential role for NKR-P1 molecules, such as those of the Ly-49 gene family, in regulating NK cell function.

Natural Killer Cell Development and Function Precede αβ T Cell Differentiation in Mouse Fetal Thymic Ontogeny

Natural killer (NK) cells mediate MHC-unrestricted cytolysis of virus-infected cells and tumor cells. In the adult mouse, NK cells are bone marrow-derived lymphocytes that mature predominantly in extrathymic locations but have also been suggested to share a common intrathymic progenitor with T lymphocytes. However, mature NK cells are thought to be absent in mouse fetal ontogeny. We report the existence of thymocytes with a mature NK cell phenotype (NK1.1+/CD117−) as early as day 13 of gestation, approximately 3 days before the appearance of CD4+/CD8+ cells in T lymphocyte development. These mature fetal thymic NK cells express genes associated with NK cell effector function and, when freshly isolated, display MHC-unrestricted cytolytic activity in vitro. Moreover, the capacity of fetal thymic NK cells for sustained growth both in vitro and in vivo, in addition to their close phenotypic resemblance to early precursor thymocytes, confounds previous assessments of NK lineage precursor function. Thus, mature NK cells may have been inadvertently included in previous attempts to identify multipotent and bipotent precursor thymocytes. These results provide the first evidence of functional NK lymphocytes in mouse fetal ontogeny and demonstrate that NK cell maturation precedes αβ T cell development in the fetal thymus.