Rat pheochromocytoma PC12 cells were permanently transfected with a plasmid vector, containing the gene of human immunodeficiency virus type 1 (HIV-1). Various clones were obtained showing the production of different levels of bioactive Tat protein (Tat) after transient contransfection with an HIV-1 long terminal repeat-chloramphenicol acetyltransferase reporter plasmid. Under conditions of serum starvation, -positive PC12 clones expressing high levels of Tat showed a significantly ( < 0.05) higher proliferation rate with respect to both mock-transfected PC12 cells and -positive PC12 cells expressing lower levels of Tat. Moreover, all -positive PC12 cell clones showed a partial morphological differentiation into sympathetic-like neurons, when seeded in low density (5 × 10 cells/cm) cultures. On the other hand, mock-transfected PC12 cells showed the round shaped morphology typical of untreated PC12 cells and displayed signs of neuronal differentiation only after treatment with 100 ng/ml of nerve growth factor. The addition of 5 µg/ml of anti-Tat monoclonal antibody to the culture medium of -positive PC12 cell clones almost completely blocked their increased proliferation rate ( < 0.05), but did not affect neuronal differentiation. A significant ( < 0.05) increase in cell proliferation was consistently observed in PC12 cells supplemented with low concentrations of Tat (5 to 25 ng/ml), whereas neuronal differentiation was hardly affected by exogenous Tat. Our data strongly suggest that Tat exerts a complex influence on the proliferation and differentiation of PC12 cells, and this might help in increasing understanding of the pathogenesis of the frequent neurological disorders observed in AIDS patients.


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