Transcription originating in the long terminal repeats of the endogenous mouse mammary tumor virus MTV-3 is activated in Stat5a-null mice and picks Up hitchhiking exons

APOBEC3 enzymes restrict marginal zone B cells

In general, a long-lasting immune response to viruses is achieved when they are infectious and replication competent. In the mouse, the neutralizing antibody response to Friend murine leukemia virus is contributed by an allelic form of the enzyme Apobec3 (abbreviated A3). This is counterintuitive because A3 directly controls viremia before the onset of adaptive antiviral immune responses. It suggests that A3 also affects the antibody response directly. Here, we studied the relative size of cell populations of the adaptive immune system as a function of A3 activity. We created a transgenic mouse that expresses all seven human A3 enzymes and compared it to WT and mouse A3-deficient mice. A3 enzymes decreased the number of marginal zone B cells, but not the number of follicular B or T cells. When mouse A3 was knocked out, the retroelement hitchhiker-1 and sialyl transferases encoded by genes close to it were overexpressed three and two orders of magnitude, respectively. We suggest that A3 shifts the balance, from the fast antibody response mediated by marginal zone B cells with little affinity maturation, to a more sustained germinal center B-cell response, which drives affinity maturation and, thereby, a better neutralizing response.

Targeting janus kinase 2 in Her2/neu-expressing mammary cancer: Implications for cancer prevention and therapy

The Janus kinase 2 (Jak2) is essential for normal mammary gland development, but this tyrosine kinase and its main effector, signal transducer and activator of transcription 5, are also active in a significant subset of human breast cancers. We have recently reported that Jak2 controls the expression and nuclear accumulation of cyclin D1. Because this particular D-type cyclin has been suggested to be a key mediator for ErbB2-associated mammary tumorigenesis, we deleted Jak2 from ErbB2-expressing mammary epithelial cells prior to tumor onset and in neoplastic cells to address whether this tyrosine kinase plays a role in the initiation as well as progression of mammary cancer. Similar to cyclin D1-deficient mice, the functional ablation of Jak2 protects against the onset of mammary tumorigenesis. In contrast, the deletion of Jak2 from neoplastic cells or the acute, ligand-inducible down-regulation of this tyrosine kinase in an orthotopic transplant model did not affect the growth and survival of cancer cells. The constitutive activation of ErbB2 signaling, which is an initial event in the formation of mammary cancer, was able to override the functional role of Jak2 in regulating the expression of Akt1 and cyclin D1. This might be a compensatory mechanism that explains why Jak2 is a relevant target for preventing the initiation but not the progression of ErbB2-associated mammary cancer.

A 5' distal palindrome within the mouse mammary tumor virus-long terminal repeat recruits a mammary gland-specific complex and is required for a synergistic response to progesterone plus prolactin

Progesterone (P) and prolactin (PRL) fulfill crucial roles during growth and differentiation of the mammary epithelium, and each has been implicated in the pathogenesis of mammary cancer. We previously identified that these hormones synergistically stimulate the proliferation of mouse mammary epithelial cells in vivo, although the mechanism(s) underlying their cooperative effect are unknown. We now report a novel pathway by which P and PRL synergize to activate transcription from the long terminal repeat (LTR) of the mouse mammary tumor virus-LTR (MMTV-LTR) in T47D breast cancer cells. Using serial 5' and 3' deletions of the MMTV-LTR, in addition to selective mutations, we identified that a previously uncharacterized inverted palindrome on the distal enhancer (-941/-930), in addition to a signal transducer and activator of transcription 5 site, was essential for the synergistic activation of transcription by P and PRL. Notably, hormone synergy occurred via a mechanism that was independent of the P receptor DNA-binding elements found in the proximal MMTV-LTR hormone-response element. The palindrome specifically recruited a protein complex (herein termed mammary gland-specific complex) that was almost exclusive to normal and cancerous mammary cells. The synergy between P and PRL occurred via a Janus kinase 2 and c-Src/Fyn-dependent signaling cascade downstream of P and PRL receptors. Combined, our data outline a novel pathway in T47D cells that may facilitate the action(s) of P and PRL during mammary development and breast cancer.

Representational difference analysis in a lupus-prone mouse strain results in the identification of an unstable region of the genome on chromosome 11

BXSB mice develop a lupus-like autoimmune syndrome. We have previously identified several intervals that were linked to disease and, in an attempt to characterise lupus susceptibility genes within these intervals, we have sought to isolate differentially expressed genes. Representational difference analysis was used to compare gene expression between BXSB and C57BL/10 mice using spleen and thymus as a source of mRNA. The majority of differentially expressed sequences identified were immunoglobulin and gp70-related sequences, overexpression of these being characteristic of the disease. Among other isolated sequences were a sialyltransferase gene, a mouse tumour virus superantigen gene (Mtv-3), and the virus-related sequence, hitchhiker. In BXSB the sialyltransferase gene not only overexpressed spliced transcripts, but also produced high levels of unspliced mRNA. Further analysis demonstrated that the copy number of the three linked sequences: sialyltransferase, Mtv-3 and hitchhiker, was amplified in BXSB and that the structural organisation of this locus varies in different mouse strains. This locus consists of three parts, Mtv-3-hitchhiker-sialyltransferase, hitchhiker-sialyltransferase, and sialyltransferase alone. Different combinations of the regions are present in different mouse strains. Linkage analysis demonstrated that this region at the distal end of chromosome 11 is weakly linked to phenotypic markers of disease.

The microarray explorer tool for data mining of cDNA microarrays: application for the mammary gland

The Microarray Explorer (MAExplorer) is a versatile Java-based data mining bioinformatic tool for analyzing quantitative cDNA expression profiles across multiple microarray platforms and DNA labeling systems. It may be run as either a stand-alone application or as a Web browser applet over the Internet. With this program it is possible to (i) analyze the expression of individual genes, (ii) analyze the expression of gene families and clusters, (iii) compare expression patterns and (iv) directly access other genomic databases for clones of interest. Data may be downloaded as required from a Web server or in the case of the stand-alone version, reside on the user's computer. Analyses are performed in real-time and may be viewed and directly manipulated in images, reports, scatter plots, histograms, expression profile plots and cluster analyses plots. A key feature is the clone data filter for constraining a working set of clones to those passing a variety of user-specified logical and statistical tests. Reports may be generated with hypertext Web access to UniGene, GenBank and other Internet databases for sets of clones found to be of interest. Users may save their explorations on the Web server or local computer and later recall or share them with other scientists in this groupware Web environment. The emphasis on direct manipulation of clones and sets of clones in graphics and tables provides a high level of interaction with the data, making it easier for investigators to test ideas when looking for patterns. We have used the MAExplorer to profile gene expression patterns of 1500 duplicated genes isolated from mouse mammary tissue. We have identified genes that are preferentially expressed during pregnancy and during lactation. One gene we identified, carbonic anhydrase III, is highly expressed in mammary tissue from virgin and pregnant mice and in gene knock-out mice with underdeveloped mammary epithelium. Other genes, which include those encoding milk proteins, are preferentially expressed during lactation.