Epidermal growth factor regulates topoisomerase II activity and drug sensitivity in human KB cells.

Because of its unique DNA-cleaving and strand-passing activities, topoisomerase II is involved in many aspects of DNA metabolism, including replication, transcription, recombination, and repair. The cytotoxic potential of topoisomerase II-targeted drugs, such as etoposide, is related to their ability to stabilize covalently linked enzyme-DNA complexes, which are intermediates in the enzyme's catalytic cycle. Epidermal growth factor receptor is expressed on the cell surface of the majority of squamous cell carcinomas, and epidermal growth factor binding is known to stimulate a number of cellular transduction pathways, including tyrosine kinase, protein kinase C, and phospholipase C.

Binding, uptake, and release of nicotine by human gingival fibroblasts.

Previous studies of the effects of nicotine on fibroblasts have reported an altered morphology and attachment of fibroblasts to substrates and disturbances in protein synthesis and secretion. This altered functional and attachment response may be associated with changes in the cell membrane resulting from binding of the nicotine, or to disturbances in cell metabolism as a result of high intracellular levels of nicotine. The purpose of the present study, therefore, was to 1) determine whether gingival fibroblasts bound nicotine and if any binding observed was specific or non-specific in nature; 2) determine whether gingival fibroblasts internalized nicotine, and if so, at what rate; 3) determine whether gingival fibroblasts also released nicotine back into the extracellular environment; and 4) if gingival fibroblasts release nicotine intact or as a metabolite.

Binding and uptake of N-nitrosonornicotine by oral epithelial cells.

N-nitrosonornicotine (NNN), a significant nitrosamine component of tobacco binds to and is taken up by cells prior to its activation by intracellular enzymes. A variety of factors may affect the binding of substances to a cell including the cell type, medium composition and the cell membrane lipid composition. This study examines the binding and uptake of NNN to various cell types and relates these to the cells' lipid composition.