Salivary Tick Cystatin OmC2 Targets Lysosomal Cathepsins S and C in Human Dendritic Cells

Abstract

To ensure successful feeding tick saliva contains a number of inhibitory proteins that interfere with the host immune response and help to create a permissive environment for pathogen transmission. Among the potential targets of the salivary cystatins are two host cysteine proteases, cathepsin S, which is essential for antigen- and invariant chain-processing, and cathepsin C (dipeptidyl peptidase 1, DPP1), which plays a critical role in processing and activation of the granule serine proteases. Here, the effect of salivary cystatin OmC2 from Ornithodoros moubata was studied using differentiated MUTZ-3 cells as a model of immature dendritic cells of the host skin. Following internalization, cystatin OmC2 was initially found to inhibit the activity of several cysteine cathepsins, as indicated by the decreased rates of degradation of fluorogenic peptide substrates. To identify targets, affinity chromatography was used to isolate His-tagged cystatin OmC2 together with the bound proteins from MUTZ-3 cells. Cathepsins S and C were identified in these complexes by mass spectrometry and confirmed by immunoblotting. Furthermore, reduced increase in the surface expression of MHC II and CD86, which are associated with the maturation of dendritic cells, was observed. In contrast, human inhibitor cystatin C, which is normally expressed and secreted by dendritic cells, did not affect the expression of CD86. It is proposed that internalization of salivary cystatin OmC2 by the host dendritic cells targets cathepsins S and C, thereby affecting their maturation.

Time-resolved proteomic profile of Amblyomma americanum tick saliva during feeding

“…In the soft tick Ornithodoros moubata, a cystatin was internalized by host dendritic cells and targeted cathepsin S and cathepsin C, affecting their maturation [77]. Cystatins from other tick species also have immunosuppressive functions [78][79][80]. Of the 12 cystatins identified in tick saliva from this study (S1B Fig, S1 Table), seven were secreted on or after 72 h of feeding, indicating that majority of cystatins might be involved in regulating tick feeding functions after the tick has initiated feeding.…”

Time-resolved proteomic profile ofAmblyomma americanumtick saliva during feeding

“…Several researchers have reported cystatins in other tick species indicated that they play important roles in tick feeding physiology (72). In the soft tick Ornithodoros moubata, a cystatin was internalized by host dendritic cells and targeted cathepsin S and cathepsin C, affecting their maturation (73). Cystatins from other tick species also have immunosuppressive functions (74–76).…”

The Anti-Angiogenic Activity of a Cystatin F Homologue from the Buccal Glands of Lampetra morii

“…The shortcomings of this method are that a lot of venom from the snakes is required to be collected and the relatively lower yield of the proteins, as well as the multiple steps. At present, the cystatins are usually expressed in the Pichia pastoris ( P. pastoris ) or insect cells probably due to the relatively complex structures, which might affect their expression and folding [13,16]. Actually, cystatins were usually expressed as inclusion bodies in the E. coli [33,34].…”

“…In bloodsucking animals, such as ticks, cystatins are usually expressed in their salivary glands or the midgut, which suggests that cystatins might participate in the feeding process of bloodsuckers [11,12,13,14,15]; while in snakes, the cystatins usually exist in their venom glands, which have been reported to suppress the growth, invasion, and metastasis of B16F10 cells and MHCC97H cells, as well as to inhibit tumor angiogenesis [16,17,18,19]. At present, more cystatins have been identified from venomous insects, snakes, fishes, or mollusks through gene cloning, and transcriptomic and proteomic approaches [20,21,22,23,24].…”