Iron is suspected to be involved in the induction and/or progression of various human tumors. More particularly, iron may be involved in the pathogenesis of Kaposi's sarcoma, a tumor of probable vascular origin. This study was designed to investigate the effect of iron deprivation on Kaposi's sarcoma. The effects of iron chelators and iron deprivation associated with serum withdrawal were investigated on Kaposi's sarcoma-derived spindle cells, on a transformed Kaposi's sarcoma cell line (Kaposi's sarcoma Y-1) and on endothelial cells, which are the probable progenitors of Kaposi's sarcoma cells. Desferrioxamine and deferiprone, two chemically unrelated iron chelators, induced a time- and concentration-dependent inhibition of endothelial and Kaposi's sarcoma cell growth. The inhibition of cell growth was associated with a decrease in Ki-67 and in both stable and total proliferating cell nuclear antigen expression. Inhibition of the progression through the G1-phase of the cell cycle was further evidenced by decreased expression of cyclin D1 and of p34 cyclin-dependent kinase 4. Terminal deoxynucleotidyl transferase-mediated desoxyuridinetriphosphate nick end labeling assay, flow cytometry with annexin-V-fluorescein and morphologic analysis indicated that iron chelation also induced a time- and concentration-dependent apoptosis. This apoptotic effect was prevented by the addition of exogenous iron. Induction of iron deprivation in the culture medium by serum withdrawal led to similar cell cycle effects, which, however, could only be partly reverted by the addition of exogenous iron. In conclusion, these results show that iron deprivation inhibits the growth and induces the apoptosis of Kaposi's sarcoma cells and of their putative endothelial precursors. This suggests that iron chelators may represent a potential therapeutic approach for the treatment of Kaposi's sarcoma.

Monoclonal antibodies specific to human T lymphocyte receptors are currently being used to define the biochemical structure of these proteins as well as of functionally distinct cell subsets. Since one of the antibodies (OKT3) recognizing the T3 (CD3) receptor mimics vital physiological processes involved in the activation of the immune system and has been successfully used as a therapeutical agent, we investigated one of the mechanisms underlying this antibody-receptor interaction. Our results show that after binding of OKT3, the complex (OKT3-T3) disappears rapidly from the cell surface. Using electron microscopy, we found that this down-regulation is due to the internalization of the complex. Parallel experiments performed on the T11 (CD2) and T4 (CD4)/AIDS retrovirus receptor indicate that the same mechanism applies for the down-regulation of those molecules. These data suggest that the T3, T11 and T4 receptors have a behavior comparable to other well characterized, hormonal and viral receptors; they provide information on the metabolization pathway of surface receptors and on the possible intracellular penetration of ligands like the HTLV-III/LAV agent in human T lymphocytes.

MCF-7 cells were co-transfected with the human HSP27 antisense cDNA and the neomycin resistance gene, included in the constitutive expression vector pSVL, and the phenotypical changes associated with decreased expression of the HSP27 protein were analysed. Three out of 10 neomycin-resistant clones obtained proliferated normally and showed a normal HSP27 content (Western blot). The seven other clones (designated as alpha HSP27 clones) were characterized by a dramatic growth inhibition associated with alterations in cellular morphology. Cells became progressively hypertrophied, exhibited lamellar protrusions and tended to lose contact with each other. They also acquired characteristics of secretory cells, namely the presence of numerous refractile granules and secretory canaliculi. Among the alpha HSP27 clones, two were immunocytochemically analysed for HSP27 content. Both clones were immunonegative for HSP27, contrary to parental cells and neo-transfectants. Actin immunostaining in one of these HSP27 negative clones revealed that microfilament organization changed from diffuse to punctate distribution. Our data support the current concept of a role for HSP27 in cell growth and differentiation and further suggests that this might occur through a control on actin polymerization-depolymerization.

Primary monolayer cultures were obtained in 60-mm petri dishes by incubating 3 X 10(6) isolated hepatocytes at 37 degrees C in Dulbecco's medium supplemented with 17% fetal calf serum. The ultrastructure of monolayer cells was examined after various incubation periods. Within 4 h of plating, the isolated spherical cells adhere to the plastic surface, establish their first contacts by numerous intertwined microvilli, and form new hemidesmosomes. After 12 h of culture, wide branched trabeculae of flattened polyhedral cells extend in all directions. Finally, after 24 h of culture, bile canaliculi are reconstituted, and a biliary polarity is recovered: the Golgi elements, which are scattered throughout the cytoplasm in the isolated cells, are reassembled in front of the newly formed bile canalculi, symmetrically in the adjacent cells; lysosomes are concentrated in that region, and microtubules reappear. Concomitantly, plasma membrane differentiations, namely desmosomes and tight junctions, develop. Tight junctions sealing the bile ducts constitute a barrier to the passage of ruthenium red and horseradish peroxidase. De novo formation of these junctions was studied by the freeze-etching technique: 10-nm particles compose a network of anastomosed linear arrays in the vicinity of the bile canaliculi; in the next step of differentiation, the particles fuse, form short ridge segments and finally continuous branched smooth strands, characteristic of the mature tight junction.

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