Role of leishmanial acidocalcisomal pyrophosphatase in the cAMP homeostasis in phagolysosome conditions required for intra-macrophage survival

Comparative phosphoproteomic analysis unravels MAPK1 regulated phosphoproteins in Leishmania donovani

Mitogen Activated Protein Kinase1 (MAPK1) of Leishmania donovani functions as key regulators of various cellular activities, which seem to be imperative for parasite survival, infectivity, drug resistance and post-translational modification of chaperones/co-chaperones. However, very less is known about LdMAPK1 target proteins. With recent advancements in proteomics, we aimed to identify phosphoproteins which were differentially expressed in LdMAPK1 overexpressing (Dd8++/++) and single replacement mutants (Dd8+/) as compared to wild type (Dd8+/+) parasites, utilizing LC-MS/MS approach. An in-depth label-free phospoproteomic analysis revealed that modulation of LdMAPK1 expression significantly modulates expression levels of miscellaneous phosphoproteins which may act as its targets/substrates. Out of 1974 quantified phosphoproteins in parasite, 140 were significantly differentially expressed in MAPK1 overexpressing and single replacement mutants. These differentially expressed phosphoproteins are majorly associated with metabolism, signal transduction, replication, transcription, translation, transporters and cytoskeleton/motor proteins, hence suggested that MAPK1 may act in concert to modulate global biological processes. The study further implicated possible role of LdMAPK1 in regulation and management of stress machinery in parasite through post translational modifications. Precisely, comparative phosphoproteomics study has elucidated significant role of LdMAPK1 in regulating various pathways contributing in parasite biology with relevance to future drug development. SIGNIFICANCE: MAPKinase1, the downstream kinase of MAPK signal transduction pathway, has drawn much attention as potential therapeutic drug target due to their indispensable role in survival and infectivity of Leishmania donovani. However, limited information is available about its downstream effector proteins/signaling networks. Utilizing label free LC-MS/MS analysis, phosphoproteome of LdMAPK1 over-expressing (Dd8++/++) and LdMAPK1 single replacement mutants (Dd8+/-) with wild type (Dd8+/+) parasites was compared and identified 140 LdMAPK1 modulated phosphoproteins, mainly involved in pathways like signal transduction, metabolism, transcriptional, translational, post-translational modification and regulation of heat shock proteins. Interestingly, LdMAPK1 interacts directly with only six phosphoproteins i.e. casein kinase, casein kinase II, HSP83/HSP90, LACK, protein kinase and serine/threonine protein kinase. Thus, the study elucidates significant role of LdMAPK1 in Leishmania biology which may drive drug-discovery efforts against visceral leishmaniasis.

Evaluation of Modulators of cAMP-Response in Terms of Their Impact on Cell Cycle and Mitochondrial Activity of Leishmania donovani

With the identification of novel cAMP binding effector molecules in Trypanosoma, the role of cAMP in kinetoplastida parasites gained an intriguing breakthrough. Despite earlier demonstrations of the role of cAMP in the survival of Leishmania during macrophage infection, there is essential need to specifically clarify the involvement of cAMP in various cellular processes in the parasite. In this context, we sought to gain a comprehensive understanding of the effect of cAMP analogs and cAMP-cyclic nucleotide phosphodiesterase (PDE) inhibitors on proliferation of log phase parasites. Administration of both hydrolyzable (8-pCPT-cAMP) and nonhydrolyzable analogs (Sp-8-pCPT-cAMPS) of cAMP resulted in a significant decrease of Leishmania proliferation. Among the various PDE inhibitors, etazolate was found to be potently antiproliferative. BrdU cell proliferation and K/N/F-enumeration microscopic study revealed that both cAMP analogs and selective PDE inhibitors resulted in significant cell cycle arrest at G1 phase with reduced S-phase population. Furthermore, careful examination of the flagellar motility patterns revealed significantly reduced coordinated forward flagellar movement of the promastigotes with a concomitant decrease in cellular ATP levels. Alongside, 8-pCPT-cAMP and PDE inhibitors etazolate and trequinsin showed marked reduction in mitochondrial membrane potential. Treatment of etazolate at subcytotoxic concentration to infected macrophages significantly reduced parasite burden, and administration of etazolate to Leishmania-infected BALB/c mice showed reduced liver and spleen parasite burden. Collectively, these results imply involvement of cAMP in various crucial processes paving the avenue for developing potent antileishmanial agent.