title: KP4 fungal toxin inhibits growth in Ustilago maydis by blocking calcium uptake.
abstract: KP4 is a virally encoded fungal toxin secreted by the P4 killer strain of Ustilago maydis. From our previous structural studies, it seemed unlikely that KP4 acts by forming channels in the target cell membrane. Instead, KP4 was proposed to act by blocking fungal calcium channels, as KP4 was shown to inhibit voltage-gated calcium channels in rat neuronal cells, and its effects on fungal cells were abrogated by exogenously added calcium. Here, we extend these studies and demonstrate that KP4 acts in a reversible manner on the cell membrane and does not kill the cells, but rather inhibits cell division. This action is mimicked by EGTA and is abrogated specifically by low concentrations of calcium or non-specifically by high ionic strength buffers. We also demonstrate that KP4 affects (45)Ca uptake in U. maydis. Finally, we show that cAMP and a cAMP analogue, N 6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate, both abrogate KP4 effects. These results suggest that KP4 may inhibit cell growth and division by blocking calcium-regulated signal transduction pathways.
authors.affiliation: Donald Danforth Plant Science Center, 7425 Forsyth Boulevard, Box 1098, St Louis, MO 63105, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Gage
authors.forename: J
authors.initials: J
authors.lastname: Bruenn
authors.forename: M
authors.initials: M
authors.lastname: Fischer
authors.forename: D
authors.initials: D
authors.lastname: Sanders
authors.forename: T J
authors.initials: TJ
authors.lastname: Smith
mesh_terms: D000935:Antifungal Agents / Q000737:chemistry / Q000494:pharmacology; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000737:chemistry / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D002413:Cations, Divalent / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D002473:Cell Wall / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D008670:Metals / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D008958:Models, Molecular; D009154:Mutation; D009183:Mycotoxins / Q000737:chemistry / Q000235:genetics / Q000494:pharmacology*; D014588:Ustilago / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000494:pharmacology*
chemical_list: D000935:Antifungal Agents; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D002413:Cations, Divalent; D008670:Metals; D009183:Mycotoxins; D014764:Viral Proteins; C086592:Ustilago maydis viral toxin KP4; D004533:Egtazic Acid; D000242:Cyclic AMP; D002118:Calcium