MEDIATION OF TRYPANOSOMA-CRUZI INVASION BY HEPARAN-SULFATE RECEPTORS ON HOST-CELLS AND PENETRIN COUNTER-RECEPTORS ON THE TRYPANOSOMES

Trypanosoma cruzi attaches and invades a large variety of mammalian ce lls by receptor-mediated interactions, one of them involving the bindi ng of parasite trans-sialidase to host sialyl receptors. Three proteog lycan-deficient mutants of Chinese hamster ovary (CHO) cells were used to probe the role of host heparin and heparan sulfate glycosaminoglyc ans (GAG) in T. cruzi invasion. All three mutants supported adhesion a nd infection to a much lower extent than the parental CHO cells. One o f the mutants, pgsD-677, did not express heparan sulfate while contain ing three- to four-fold excess chondroitin sulfate, yet the cell line was a poor substrate for T. cruzi adhesion. Proteoglycan-deficient cel ls obtained by inhibiting GAG synthesis in parental cells with p-nitro phenyi-beta-D-xyloside, were also poor hosts for T. cruzi invasion. Fu rthermore, digestion of parental cells with heparinase and heparitinas e, two lyases that specifically depolymerize heparin and heparan sulfa te, reduced the potential of the cells to support T. cruzi adhesion an d growth. Lyases that digested chondroitin sulfate and other GAGs did not affect T. cruzi invasion. These results suggest that heparin/hepar an sulfate epitopes are receptors for T. cruzi invasion. The correspon ding counter-receptor on T. cruzi appears to be penetrin, a heparin-bi nding protein that promotes trypanosome penetration into cells. Purifi ed penetrin caused agglutination of red blood cells, and the hemagglut ination was exquisitely sensitive to heparin and heparan sulfate. Howe ver, sialic acid and sialyl compounds did not inhibit penetrin-induced hemagglutination. Recombinant penetrin competitively inhibited T. cru zi invasion of proteoglycan-containing parental cells, but not of prot eoglycan-deficient mutants nor of heparitinase-treated cells. Furtherm ore, consistent with the sugar specificity of penetrin as a hemaggluti nin, recombinant penetrin competed for trypanosome invasion of a CHO c ell mutant (Lec2) that expresses heparan sulfate but not sialyl residu es. Given that the release of sialic acid from the proteoglycan-defici ent mutants further reduced T. cruzi invasion, as did the removal of h eparan sulfate from the Lec2 mutant, and given that penetrin does not bind to sialic acid with high affinity, the results indicate that the penetrin-heparan sulfate pathway for T. cruzi invasion is distinct fro m the trans-sialidase-sialic acid route.