The epidermal growth factor/cAMP-inducible ectoCa(2+)-ATPase of human hepatoma Li-7A cells is similar to rat liver ectoATPase/hepatocyte cell adhesion molecule (cell-CAM 105).
Human hepatoma Li-7A cells exhibit two cell surface ATPase (ectoATPase) activities distinguishable by their different biochemical properties. The activity of the minor ectoATPase, ectoCa(2+)-ATPase, is enhanced severalfold when Li-7A cells are treated simultaneously by epidermal growth factor (EGF) and cAMP elevating agents (Knowles, A. F., 1990, Arch. Biochem. Biophys. 283, 114-119). Here we report that the human ectoCa(2+)-ATPase is biochemically similar to the major rat hepatocyte ectoATPase/cell adhesion molecule (cell-CAM 105) with respect to response to divalent ions and sulfhydryl reagents. Furthermore, the binding of rat liver ectoATPase antibody increased markedly in EGF/cholera toxin/hydrocortisone-treated Li-7A cells compared to untreated cells. Western blot analysis revealed cross-reactivity of the antibody with a 125-kDa protein. Partial purification of ectoCa(2+)-ATPase from EGF/cholera toxin/hydrocortisone-treated Li-7A cells confirmed that enrichment of the 125-kDa protein correlated with an increase in ATPase activity. We conclude that EGF and increased levels of cAMP lead to increased synthesis of the ectoCa(2+)-ATPase in Li-7A cells. The present demonstration of similarity between the ectoCa(2+)-ATPase and a rat liver cell adhesion molecule, cell-CAM 105, contributes significantly to an understanding of the implication of down-regulation of ectoCa(2+)-ATPase during hepatocyte-hepatoma transformation.
Department of Biology, Northeastern University, Boston, Massachusetts 02115.
J P
JP
Gao
A F
AF
Knowles
D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000737:chemistry*; D006528:Carcinoma, Hepatocellular / Q000201:enzymology*; D002462:Cell Membrane / Q000201:enzymology; D002772:Cholera Toxin / Q000494:pharmacology; D003429:Cross Reactions; D000242:Cyclic AMP / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005110:Extracellular Space / Q000201:enzymology; D006801:Humans; D006854:Hydrocortisone / Q000494:pharmacology; D066298:In Vitro Techniques; D008099:Liver / Q000201:enzymology*; D008113:Liver Neoplasms / Q000201:enzymology*; D008274:Magnesium / Q000494:pharmacology; D008970:Molecular Weight; D051381:Rats; D014407:Tumor Cells, Cultured
D004815:Epidermal Growth Factor; D002772:Cholera Toxin; D000242:Cyclic AMP; D000251:Adenosine Triphosphatases; C027201:ectoATPase; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium; D006854:Hydrocortisone