LOCATION OF ALUMINUM AND GALLIUM IN HUMAN NEUROBLASTOMA-CELLS TREATEDWITH METAL-CHELATING AGENT COMPLEXES

The subcellular location of aluminium is unknown, probably because of difficulties in investigating aluminium biochemistry and the use of va ried experimental approaches of uncertain sensitivity. We have studied levels of uptake and the localization of gallium and of aluminium in cultured human neuroblastoma cells treated with soluble metal complexe s (mainly Al- or Ga-EDTA), radiolabeled with Al-26 Or Ga-67, respectiv ely. Crude nuclei and cytoplasm were obtained by two separate methods, and DNA, RNA, and proteins were prepared from the nuclei by centrifug ation in high salt; also, cytosol and noncytosol were separated using a nondissociating method, Levels of uptake were of similar order for t he two metals-on average about 50 pmol/10(6) cells for aluminium and 1 20 pmol/10(6) cells for gallium, after 4 to 8 days treatment at 250 mu M, and approximately 50 to 70% of the metal was found in the cytosol. About 20% of the aluminium and 10 to 25% of the gallium was associate d with nuclear protein. A lower proportion was bound to DNA and to nuc lear RNA. In cells treated with gallium-citrate/transferrin mixtures, 30 to 35% of the gallium in the cytosol was bound to protein, at least 3/5 being loosely bound; the main gallium-associated protein was prob ably intracellular transferrin. The remaining 65 to 70% of the metal i n the cytosol was in low-molecular-weight form, and we suggest that th e latter metal could affect structures such as the cytoskeleton and al so metabolic processes in the cytoplasm. The similarity in distributio n of the two metals supports the use of gallium as a ''surrogate'' for aluminium, at least in cell culture studies. (C) 1998 Academic Press.