ENTAMOEBA-HISTOLYTICA - INCREASE OF ENTEROTOXICITY AND OF 53-KDA AND 75-KDA CYSTEINE PROTEINASES IN A CLONE OF HIGHER VIRULENCE

We compared the enterotoxicity and cysteine proteinases (CP) of the lo w-virulence Entamoeba histolytica HM1 strain with the highly virulent 1659 clone, derived from HM1 by hamster liver passages. Enterotoxicity of 50,000 freeze-thawed trophozoites was determined on 0.28-cm(2) int estinal segments mounted in Ussing chambers; CP activity of Nonidet-P4 0 amebal lysates was assayed by gelatin-sodium dodecyl sulfate-polyacr ylamide gel electrophoresis and carbobenzoxy-L-arginine-L-arginyl-p-ni troaniline, a CP-specific substrate. Treatment of gerbil cecum segment s with amebal lysates caused an immediate fall of their electrophysiol ogic properties (potential difference, short-circuit current, and tran smural resistance) whose decay rates were clearly faster with 1659 tha n with HM1 lysates. Nonimmune and immune antiamebic human sera and the CP-specific inhibitor E-64 ns-epoxysuccinyl-L-leucylamido(4-guanidino )butane) prevented the fall of the electophysiologic properties. Gelat inases, less active in HM1 than in 1659 trophozoites, were better pres erved in lysates containing 10 mM p-hydroxymercuribenzoate (pHMB) to p revent autoproteolysis: in lysates without pHMB nearly no gelatinase b ands were observed in HMI samples, whereas intense 30K, 35K, 44K, and 75K bands were seen in 1659 samples; in lysates with pHMB only 53K and 75K bands were found that were much more intense in 1659 samples, 75K being barely visible in HM1 samples. The overall CP activity was 17 t imes higher in 1659 than in HM1 lysates, was inhibited by E-64 (mean i nhibitory dose, 20 mu m), was stimulated by 2-mercaptoethanol (ME) 3.7 times in HMI and 2.4 times in 1659 lysates, and was reactivated by ME in lysates containing pHMB. Most of the CP activity in HM1 lysates se dimented at 15,600g but predominated in 1659 supernatants. The increas e of E. histolytica virulence thus correlates with a remarkable increa se both of in vitro enterotoxicity and of two CPs (53K and 75K), sugge sting that these proteinases are significant pathogenicity factors. (C ) 1995 Academic Press, Inc.