Temperature-induced protein secretion by Leishmania mexicana modulates macrophage signalling and function.

Protozoan parasites of genus Leishmania are the causative agents of leishmaniasis. These digenetic microorganisms undergo a marked environmental temperature shift (TS) during transmission from the sandfly vector (ambient temperature, 25-26°C) to the mammalian host (37°C). We have observed that this TS induces a rapid and dramatic increase in protein release from Leishmania mexicana (cutaneous leishmaniasis) within 4 h. Proteomic identification of the TS-induced secreted proteins revealed 72 proteins, the majority of which lack a signal peptide and are thus thought to be secreted via nonconventional mechanisms. Interestingly, this protein release is accompanied by alterations in parasite morphology including an augmentation in the budding of exovesicles from its surface. Here we show that the exoproteome of L. mexicana upon TS induces cleavage and activation of the host protein tyrosine phosphatases, specifically SHP-1 and PTP1-B, in a murine bone-marrow-derived macrophage cell line. Furthermore, translocation of prominent inflammatory transcription factors, namely NF-κB and AP-1 is altered. The exoproteome also caused inhibition of nitric oxide production, a crucial leishmanicidal function of the macrophage. Overall, our results provide strong evidence that within early moments of interaction with the mammalian host, L. mexicana rapidly releases proteins and exovesicles that modulate signalling and function of the macrophage. These modulations can result in attenuation of the inflammatory response and deactivation of the macrophage aiding the parasite in the establishment of infection.

Comparative study of the ability of Leishmania mexicana promastigotes and amastigotes to alter macrophage signaling and functions.

Leishmania alternates between two morphologically different stages, promastigotes and amastigotes. While the majority of reports focused on how the promastigote form can alter macrophage (Mphi) signaling and function, fewer reports investigated signaling alterations mediated by amastigotes, and there is a lack of comparative studies. In this study, we performed a comparison between the ability of both forms of the parasite to alter Mphi signaling and functions. Here, we show that both promastigotes and amastigotes were able to rapidly activate host protein tyrosine phosphatases (PTPs), importantly the Src homology 2 domain-containing PTP (SHP-1). However, we found that PTP-1B is specifically activated by promastigote but not amastigote infection and that lmcpb(-/-) promastigotes were no longer able to activate PTP-1B. We also show a similarity in the way promastigotes and amastigotes inactivate the transcription factors (TFs) STAT-1alpha and AP-1, but we show differences in the modulation of NF-kappaB, with promastigotes cleaving the p65 subunit, generating a smaller p35 subunit, and amastigotes fully degrading the p65 subunit with no p35 production. Importantly, we show that the cysteine proteinase LmCPb plays a key role in the alteration of NF-kappaB, STAT-1alpha, and AP-1 by promastigote and amastigote infections, ultimately leading to the inability of these TFs to translocate to the nucleus in response to gamma interferon (IFN-gamma) stimulation and thus contributing to the ability of both parasite forms to effectively block IFN-gamma-mediated nitric oxide (NO) production in Mphis.