title: Activated K-RAS increases polyamine uptake in human colon cancer cells through modulation of caveolar endocytosis.
abstract: Endocytic pathways have been implicated in polyamine transport in mammalian cells, but specific mechanisms have not been described. We have shown that expression of a dominant negative (DN) form of the GTPase Dynamin, but not Eps15, diminished polyamine uptake in colon cancer cells indicating a caveolar and nonclathrin uptake mode. Polyamines co-sediment with lipid raft/caveolin-1 rich fractions, of the plasma membrane in a sucrose density gradient. Knock down of caveolin-1 significantly increased polyamine uptake. Conversely, ectopic expression of this protein resulted in diminished polyamine uptake. We also found that presence of an activated K-RAS oncogene significantly increased polyamine uptake by colon cancer cells. This effect is through an increase in caveolin-1 phosphorylation at tyrosine residue 14. Caveolin-1 is a negative regulator of caveolar endocytosis and phosphorylation in a K-RAS dependent manner leads to an increase in caveolar endocytosis. In cells expressing wild type K-RAS, addition of exogenous uPA was sufficient to stimulate caveolar endocytosis of polyamines. This effect was abrogated by the addition of a SRC kinase inhibitor. These data indicate that polyamine transport follows a dynamin-dependent and clathrin-independent endocytic uptake route, and this route is positively regulated by the oncogenic expression of K-RAS in a caveolin-1 dependent manner.
authors.affiliation: Biochemistry and Molecular and Cellular Biology Graduate Program, University of Arizona, Tucson, Arizona, USA.
authors.forename: Upal K Basu
authors.initials: UK
authors.lastname: Roy
authors.forename: Nathaniel S
authors.initials: NS
authors.lastname: Rial
authors.forename: Karen L
authors.initials: KL
authors.lastname: Kachel
authors.forename: Eugene W
authors.initials: EW
authors.lastname: Gerner
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D001692:Biological Transport; D015153:Blotting, Western; D002135:Calcium-Binding Proteins / Q000378:metabolism; D021941:Caveolae / Q000502:physiology*; D051242:Caveolin 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D003110:Colonic Neoplasms / Q000378:metabolism* / Q000473:pathology; D034281:Dynamins / Q000378:metabolism; D004705:Endocytosis; D011905:Genes, ras / Q000502:physiology*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D021962:Membrane Microdomains; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011073:Polyamines / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002135:Calcium-Binding Proteins; D051242:Caveolin 1; C486206:EPS15 protein, human; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; D011073:Polyamines; D014443:Tyrosine; D034281:Dynamins