Trypanosome trans-sialidase targets TrkA tyrosine kinase receptor and induces receptor internalization and activation.

Trypanosome trans-sialidase (TS) is a sialic acid-transferring enzyme that hydrolyzes alpha2,3-linked sialic acids and transfers them to acceptor molecules. Here we show that a highly purified recombinant TS derived from T. cruzi parasites targets TrkA receptors on TrkA-expressing PC12 cells and colocalizes with TrkA internalization and phosphorylation (pTrkA). Maackia amurensis lectin II (MAL-II) and Sambucus nigra lectin (SNA) block TS binding to TrkA-PC12 cells in a dose-dependent manner with subsequent inhibition of TS colocalization with pTrkA. Cells treated with lectins alone do not express pTrkA. The catalytically inactive mutant TSDeltaAsp98-Glu also binds to TrkA-expressing cells, but is unable to induce pTrkA. TrkA-PC12 cells treated with a purified recombinant alpha2,3-neuraminidase (Streptococcus pneumoniae) express pTrkA. Wild-type TS but not the mutant TSDeltaAsp98-Glu promotes neurite outgrowth in TrkA-expressing PC12 cells. In contrast, these effects are not observed in TrkA deficient PC12nnr5 cells but are reestablished in PC12nnr5 cells stably transfected with TrkA and are significantly blocked by inhibitors of tyrosine kinase (K-252a) and MAP/MEK protein kinase (PD98059). Together these observations suggest for the first time that hydrolysis of sialyl alpha2,3-linked beta-galactosyl residues of TrkA receptors plays an important role in TrkA receptor activation, sufficient to promote cell differentiation (neurite outgrowth) independent of nerve growth factor.