The 5'¯anking region of the C3(1) component of the rat prostate steroid binding protein (PSBP) has been used to successfully target the expression of the SV40 large Tantigen (Tag) to the epithelium of both the mammary and prostate glands resulting in models of mammary and prostate cancers which histologically resemble the human diseases. Atypia of the mammary ductal epithelium develops at about 8 weeks of age, progressing to mammary intraepithelial neoplasia (resembling human ductal carcinoma in situ [DCIS]) at about 12 weeks of age with the development of invasive carcinomas at about 16 weeks of age in 100% of female mice. The carcinomas share features to what has been classi®ed in human breast cancer as in®ltrating ductal carcinomas. All FVB/N female mice carrying the transgene develop mammary cancer with about a 15% incidence of lung metastases. Approximately 10% of older male mice develop anaplastic mammary carcinomas. Unlike many other transgenic models in which hormones and pregnancy are used to induce a mammary phenotype, C3(1)/Tag mice develop mammary tumors in the mammary epithelium of virgin animals without hormone supplementation or pregnancy. Although mammary tumor development appears hormone-responsive at early stages, invasive carcinomas are hormone-independent, which corresponds to the loss of estrogen receptor-a expression during tumor progression. Molecular and biologic factors related to mammary tumor progression can be studied in this model since lesions evolve over a predictable time course. Genomic alterations have been identi®ed during tumor progression, including an ampli®cation of the distal portion of chromosome 6 containing ki-ras and loss of heterozygosity (LOH) in other chromosomal regions. We have demonstrated that stage speci®c alterations in the expression of genes which are critical regulators of the cell cycle and apoptosis are functionally important in vivo. C3(1)/Tag mice appear useful for testing particular therapies since growth of the mammary tumors can be reduced using chemopreventive agents, cytokines, and an anti-angiogenesis agent.

Effects of the lipid mediator lysophosphatidic acid (LPA) were studied on the cerebral circulation of newborn pigs using closed cranial windows. Topical application of synthetic LPA caused dose-dependent vasoconstriction and inhibited vasodilation to hypercapnia and isoproterenol. These vasodilators elicited a rise in the adenosine 3',5'-cyclic monophosphate (cAMP) content of the cerebrospinal fluid, which was inhibited dose dependently by LPA. Pertussis toxin (1 microgram/ml) completely abolished LPA-induced vasoconstriction and the altered vascular reactivity, and LPA no longer decreased cAMP. Electrophysiological recording of currents evoked by LPA-like lipids in Xenopus oocytes showed that cerebrospinal fluid is normally devoid of LPA-like factors. In contrast, the amount of LPA-like factors generated 4 days after intrathecal injection of autologous blood was in the range of 1-10 microM LPA equivalents. The data indicate that LPA-like bioactive mediators were generated in an intracranial hematoma model and that these phospholipids might play a role in the pathophysiology of altered vascular reactivity often found in posthemorrhagic conditions and could also contribute to the development of posthemorrhagic vasoconstriction.

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The dramatic increase in apoptosis observed during the development of preneoplastic mammary lesions is associated with a significant elevation in Bax expression in C3(1)/SV40 large T antigen (TAg) transgenic mice. The significance of Bax expression during tumor progression in vivo was studied by generating double-transgenic mice carrying the C3(1)/TAg transgene and mutant alleles for bax. C3(1)/TAg transgenic mice carrying mutant bax alleles exhibited accelerated rates of tumor growth, increased tumor numbers, larger tumor mass and decreased survival rates compared with mice carrying wild-type bax. Accelerated tumorigenesis associated with the bax+/- genotype did not require the loss of function of the second bax allele. Thus, haploid insufficiency of bax is enough to accelerate tumor progression, suggesting that the protective effect of Bax is dose-dependent. While levels of apoptosis in the preneoplastic lesions, but not carcinomas, were reduced in bax+/- or bax-/- mice compared with bax+/+ mice, rates of cellular proliferation in mammary lesions were similar among all bax genotypes. These data demonstrate that bax is a critical suppressor of mammary tumor progression at the stage of preneoplastic mammary lesion development through the upregulation of apoptosis, but that this protective effect is lost during the transition from preneoplasia to invasive carcinoma.