title: Enhancement of ricin cytotoxicity in Chinese hamster ovary cells by depletion of intracellular K+: evidence for an Na+/H+ exchange system in Chinese hamster ovary cells.
abstract: Depletion of intracellular K+ has been reported to result in an arrest of the formation of coated pits in human fibroblasts (Larkin, J.M., M.S. Brown, J.L. Goldstein, and R.G.W. Anderson, 1983, Cell, 33:273-285). We have studied the effects of K+ depletion on the cytotoxicities of ricin, Pseudomonas exotoxin A, and diphtheria toxin in Chinese hamster ovary (CHO) cells. The cytotoxicities of ricin and Pseudomonas toxin were enhanced in K+-depleted CHO cells whereas the cytotoxicity of diphtheria toxin was reduced by K+ depletion. The effects of NH4Cl on the cytotoxicities of ricin, Pseudomonas toxin, and diphtheria toxin were found to be similar to those of K+ depletion, and there were no additive or synergistic effects on ricin cytotoxicity by NH4Cl in K+-depleted medium. The enhancement of ricin cytotoxicity by K+ depletion could be completely reversed by the addition of K+, Rb+, and partially by the addition of Cs+, before the ricin treatment, whereas Li+ was ineffective. These protective effects of K+ or Rb+ requires a functional Na+/K+ ATPase. CHO cells grown in K+-depleted media were found to contain 6.3-fold increase in intracellular Na+ level, concomitant with a 10-fold reduction in intracellular K+ level. The enhanced cytotoxicity of ricin in K+-free medium and the increased uptake of Na+ could be abolished by amiloride or amiloride analogues, which are known to be potent inhibitors of the Na+/H+ antiport system. Our results suggest that a depletion of intracellular K+ results in an influx of Na+, which is accompanied by the extrusion of H+. Consequently, there is an alkalinization of the cytosol and the ricin-containing endosomes. As a result, ricin is more efficiently released from the endosomes in-K+-depleted cells. Results from the studies of the binding, internalization, and degradation of 125I-ricin, and the kinetics of inhibition of protein synthesis by ricin in K+-depleted cells are consistent with this working hypothesis.
authors.forename: P C
authors.initials: PC
authors.lastname: Ghosh
authors.forename: R B
authors.initials: RB
authors.lastname: Wellner
authors.forename: E J
authors.initials: EJ
authors.lastname: Cragoe
authors.forename: H C
authors.initials: HC
authors.lastname: Wu
mesh_terms: D036002:ADP Ribose Transferases; D000584:Amiloride / Q000494:pharmacology; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D001427:Bacterial Toxins; D001665:Binding Sites; D002460:Cell Line; D006224:Cricetinae; D003470:Culture Media; D003603:Cytotoxins / Q000633:toxicity*; D004167:Diphtheria Toxin / Q000494:pharmacology; D005098:Exotoxins / Q000494:pharmacology; D005260:Female; D007700:Kinetics; D009550:Nigericin / Q000494:pharmacology; D010053:Ovary / Q000166:cytology* / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D011522:Protons; D011550:Pseudomonas aeruginosa; D012276:Ricin / Q000378:metabolism / Q000633:toxicity*; D012964:Sodium / Q000378:metabolism*; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A
chemical_list: D036002:ADP Ribose Transferases; D000584:Amiloride; D000643:Ammonium Chloride; D001427:Bacterial Toxins; D003470:Culture Media; D003603:Cytotoxins; D004167:Diphtheria Toxin; D005098:Exotoxins; D009550:Nigericin; D011188:Potassium; D011522:Protons; D012276:Ricin; D012964:Sodium; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A