title: Mechanisms involved in the cellular uptake of hematoporphyrin by rat hepatoma cells.
abstract: To clarify the mechanisms involved in the specific uptake of hematoporphyrin by cancer cells, we investigated the interaction of the heme- and/or hematoporphyrin-hemopexin complexes with rat hepatoma dRLh-84 cells. Hemopexin bound to the cells in a saturable, time- and temperature-dependent manner. The cells exhibited 0.55 nmol of binding sites/mg of protein for the heme-hemopexin complex and 0.38 nmol for the hematoporphyrin-hemopexin complex. The dissociation constants (Kd) for the heme-hemopexin and hematoporphyrin-hemopexin complexes were 0.57 and 0.54 microM, respectively. Specific binding of the labeled hemopexin was inhibited by the unlabeled heme- and hematoporphyrin-hemopexin complexes but was unaffected by albumin or neoglycoprotein. Hematoporphyrin bound to hemopexin was incorporated into the cells at 37 degrees C, but not at 4 degrees C. These results indicate that hematoporphyrin bound hemopexin was taken up by dRLh-84 cells, via the hemopexin receptors. When the hematoporphyrin-albumin complex was incubated with the cells, the hematoporphyrin-[125I]albumin complex bound to the cells in a time and temperature-dependent manner. Here the binding was not saturated up to 100 micrograms/ml of albumin. The binding of hematoporphyrin-[125I]albumin was partially inhibited by unlabeled albumin and hemopexin. Hematoporphyrin bound to albumin was taken up by the cells at 37 degrees C. Thus, the albumin-dependent uptake of hematoporphyrin by rat hepatoma dRL-84 cells could be differentiated from the hemopexin-mediated uptake of hematoporphyrin.
authors.affiliation: Third Department of Internal Medicine, Kansai Medical University, Osaka.
authors.forename: Y
authors.initials: Y
authors.lastname: Naitoh
authors.forename: S
authors.initials: S
authors.lastname: Taketani
authors.forename: R
authors.initials: R
authors.lastname: Tokunaga
authors.forename: Y
authors.initials: Y
authors.lastname: Sameshima
mesh_terms: D000418:Albumins / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D002462:Cell Membrane / Q000378:metabolism; D006415:Hematoporphyrins / Q000378:metabolism*; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism; D018000:Receptors, Peptide; D013696:Temperature; D014407:Tumor Cells, Cultured
chemical_list: D000418:Albumins; D006415:Hematoporphyrins; D011956:Receptors, Cell Surface; D018000:Receptors, Peptide; C047453:hemopexin receptor