Transforming growth factor-alpha expression in peritoneal macrophages elicited from SENCAR and B6C3F1 mice: responses to lipopolysaccharide and 12-O-tetradecanoylphorbol-13-acetate

Transforming growth factor alpha binds to Trypanosoma cruzi amastigotes to induce signaling and cellular proliferation

Macrophages secrete transforming growth factor alpha (TGF-alpha) to trigger proliferation of cancer cells. Here, we report a new role for TGF-alpha in modulating the direct cellular proliferation of a parasitic protozoan, Trypanosoma cruzi. Amastigotes present two classes of receptors for TGF-alpha with different binding affinities. (125)I-TGF-alpha binding was competed by an excess of cold epidermal growth factor and TGF-alpha but not by an irrelevant molecule. Upon binding of TGF-alpha to amastigotes, the ligand is internalized, inducing trypanosome tyrosine phosphorylation of 90- and 87-kDa proteins and increasing DNA synthesis and proliferation of amastigotes. Furthermore, exposure of macrophages to TGF-alpha induced increased amastigote proliferation. These results describe a novel mechanism used by amastigotes to regulate their proliferation mediated by a TGF-alpha-dependent signal transduction pathway.

Effect of low dietary calcium on bone metabolism in the SENCAR mouse

The SENCAR (sensitive to carcinogenesis) mouse is a unique tool for investigating the interaction between a specific defect in intracellular signaling, dietary calcium, and metabolic bone disease. The SENCAR mouse was developed by selective breeding for enhanced sensitivity to two-stage carcinogenesis. Its major genetic defect, which renders it exquisitely sensitive to stimulation with diacylglycerol or phorbol esters, is in the regulatory domain of protein kinase C, one of the primary intracellular mediators of hormonal effects. At sexual maturity, SENCAR mice are large and have big bones, but our previous pharmacokinetic studies showed that they accumulate less calcium under normal conditions and lose more calcium under adverse conditions than do other, standard strains of mice. To histologically define the effect of low dietary calcium on bone metabolism, we performed histomorphometric analysis of tetracycline-labeled sections of femoral bone from male SENCAR mice maintained on calcium-sufficient and calcium-deficient diets during the critical period from 10 to 14 weeks of age. The bone volume, absolute osteoid volume, and mineral apposition rate were lower at 14 than at 10 weeks of age in SENCAR mice fed 0.02 or 0.6% calcium diets. Calcium deficiency increased the architectural disarray and the probability of observing focal discontinuities in the growth plate. Thus, characteristic features of impaired bone metabolism (low bone volume and apposition rate) develop early in SENCAR mice and are exacerbated by low dietary calcium. Detailed examinations of the histology and biochemistry of SENCAR mouse bone will provide insights into the mechanisms by which specific defects in the signal transduction of protein kinase C contribute to impaired bone metabolism.

HIV-1 envelope glycoprotein 120 regulates brain IL-1beta system and TNF-alpha mRNAs in vivo

Human immunodeficiency virus type I (HIV-1)-derived envelope glycoprotein 120 (gp120) is proposed to play an important role in HIV-1 neuropathology. Gp120 may act through mediators including proinflammatory cytokines. Here, we investigated the regulation of the IL-1beta system [IL-1beta, IL-1 receptor type I (IL-1RI), IL-1 receptor antagonist (IL-1Ra)], TNF-alpha and TGF-alpha mRNAs in the rat central nervous system (CNS) in response to the constant intracerebroventricular (ICV) microinfusion of HIV-1 gp120 for 72 h and 144 h. The results show that gp120: (1) increased IL-1beta and IL-1Ra mRNAs levels in the same samples from the cerebellum, hypothalamus and midbrain, with the largest increase in the hypothalamus; (2) induced profiles of IL-1beta mRNA and IL-1Ra mRNA that were highly intercorrelated; (3) increased the hypothalamic TNF-alpha mRNA levels; and (4) did not affect the IL-1RI mRNA and TGF-alpha mRNA levels in any brain region. A dysregulation in the IL-1beta/IL-1Ra CNS balance and a mutual induction and synergistic activity of IL-1beta and TNF-alpha could result in a deleterious amplification cycle of cellular activation and cytotoxicity with implications to HIV-1-associated encephalitis, encephalopathy, and neurological manifestations.