Expression of pro form of prostate-specific antigen by mammalian cells and its conversion to mature, active form by human kallikrein 2

To study the expression, biosynthesis, and processing of prostate-specific antigen (PSA) in mammalian cells, recombinant PSA was expressed in Syrian hamster tumor cell line AV12-664 (AV12-PSA). Expression of PSA was monitored by the Tandem-MP PSA assay. PSA was secreted into the medium during the logarithmic phase of cell growth at >9 microg/ml and was stable. The PSA purified from spent medium of AV12-PSA cells did not exhibit any enzymatic activity and did not complex with the protease inhibitor, alpha-1-antichymotrypsin. These findings indicated that an inactive form of PSA was expressed by AV12-PSA cells. NH2-terminal sequencing confirmed the identity of the PSA purified from the spent medium of AV12-PSA cells to be pro-PSA. This demonstrates that PSA is expressed as pro-PSA by mammalian cells and suggests that pro-PSA may be present in biological fluids. Human kallikrein 2 (hK2), another member of the hK family, is also expressed predominantly in prostate epithelium. Although hK2 has been shown to exhibit trypsin-like activity, little is known about its natural substrates. Using purified proteins, we show that hK2 can convert pro-PSA to mature, enzymatically active PSA, thus establishing a physiological connection between hK2 and PSA. These findings imply that hK2 may be regulating PSA activity in vivo.     

Thymic alterations in feline GM1 gangliosidosis

GM1 gangliosidosis is an inherited metabolic disease characterized by progressive neurological deterioration with premature death seen in children and numerous animals, including cats. We have observed that thymuses from affected cats greater than seven months of age (GM1 mutant cats) show marked thymic reduction compared to age-matched normal cats. The studies reported here were done to describe alterations in the thymus prior to (less then 90 days of age) and during the development of mild (90 to 210 days of age) to severe (greater than 210 days of age) progressive neurologic disease and to explore the pathogenesis of the thymic abnormality. Although histologic examination of the thymus from GM1 affected cats less than 210 days of age showed no significant differences from age-matched control cats, thymuses from GM1 mutant cats greater than 210 days of age were significantly reduced in size (approximately 3-fold). Histologic sections of lymph nodes, adrenal glands, and spleens from GM1 gangliosidosis-affected cats showed no significant differences. Flow cytometric analyses showed a marked decrease in the percentage of immature CD4+CD8+ thymocytes (p < 0.001) and significantly increased CD4-CD8+ cells (p < 0.01) in GM1 mutant cats greater than 210 days of age when compared to normal age matched cats. Co-labelling with CD4, CD8, and CD5 indicated an increase in the percentage of GM1 mutant cat thymocytes at this age which were CD5high, suggesting the presence of more mature cells. Cytometric analyses of subpopulations of peripheral lymphocytes indicated an increase in CD4-CD8+ cells (p < 0.05) with concurrent decreases in CD4+CD8- and CD4-CD8- cells (which were not significant). Similar analyses of thymocyte and lymphocyte subpopulations from cats < 210 days of age showed no significant differences between GM1 mutant and normal cells. GM1 mutant cats at all ages had increased surface binding of Cholera toxin B on thymocytes, indicating increased surface GM1 ganglioside expression. Increases were highly significant in GM1 mutant cats greater than 210 days of age. In situ labelling for apoptosis was increased in GM1 mutant cats between 90 to 200 days of age when thymic masses were within normal limits. In GM1 mutant cats over 200 days of age, decreased labelling was observed when thymic mass was reduced and the CD4+CD8+ subpopulation, known to be very susceptible to apoptosis, was significantly decreased. These data describe premature thymic involution in feline GM1 gangliosidosis and suggest that increased surface GM1 gangliosides alters thymocyte development in these cats.     

Immunohistochemical and morphological characterization of spontaneously occurring pheochromocytomas in the aging mouse

Pheochromocytomas in mice are rare tumors, and their expression of functional markers has not previously been assessed. In this study, 29 spontaneously occurring mouse pheochromocytomas were characterized morphologically and immunohistochemically to determine whether there are functional correlates to previously described morphological features and to provide a database for comparison with tumors that arise in genetically engineered animals. The tumors were derived from 28 mice 828-1,489 days old, of three genotypes. Considerable cytological and architectural polymorphism was observed both within and between tumors. Most of the tumor cells were comparable in size to normal chromaffin cells or were larger. Small basophilic cells, which are the predominant cell type in rat pheochromocytomas, were usually in the minority. All of the tumors and most of the cells within individual tumors expressed immunoreactive tyrosine hydroxylase (TH). The tumors were variably positive for phenylethanolamine-N-methyltransferase (PNMT) and chromogranin A (CGA). There did not appear to be a global association of specific cytological features with expression of TH, PNMT, or CGA, although cells of similar appearance often shared similar immunoreactivities within individual tumors. Small basophilic cells could be either PNMT-positive or PNMT-negative. The frequency, morphology, and immunophenotype of mouse pheochromocytomas suggest that the mouse may be more appropriate than the rat as a model for human adrenal medullary pathology. In addition, the expression of immunoreactive PNMT by mouse pheochromocytomas suggests that these tumors are a potential source of epinephrine-producing cell lines, for which adequate models currently do not exist.     

Rate of HIV-1 decline following antiretroviral therapy is related to viral load at baseline and drug regimen

OBJECTIVES AND DESIGN: The dynamics uf viral decline following the initiation of antiretroviral treatment were studied in 29 HIV-1-infected patients participating in a two-arm trial comparing immediate (group A: ritonavir, zidovudine and lamivudine) and delayed (group B: ritonavir supplemented by zidovudine and lamivudine on day 21) triple therapy. Parameters underlying viral dynamics were estimated using mathematical models tailored to these treatment protocols. RESULTS: The decline in plasma HIV-1 density between day 0 and 21 was steeper in group A (-2.27+/- 0.46 log10) than group B (-1.87+/-0.56 log10). In a subset of patients amenable to full mathematical analysis, a short-lived productively infected cell compartment (producing approximately 97% of total virions) decayed with a half-life of 1.0-2.5 days, whereas a long-lived infected cell compartment decayed with a half-life of 18.8-32.8 days. Estimates for the time for the elimination of virus from these two cell populations ranged from 474 to 802 days. The rate of loss of productively infected CD4+ T cells was positively correlated with baseline viral load in group A and in the combined dataset. CONCLUSIONS: These results suggest that HIV-infected cell populations may have a faster turnover in patients with higher viral loads due to higher infection rate parameters, higher rates of virus production, or lower virus clearance rates.