Phosphatases for and against: Trichuris vs. Leishmania

Posted by Kasra

Trichuris trichiura adult male

Trichuris trichiura adult male – Image taken from DPDx

Trichuris, is an intestinal roundworm, also known as whipworm, that can be transmitted through ingestion of food contaminated with its eggs. The larvae hatch inside the small intestine and complete their life cycle to adults in the cecum. After maturation, which can take about 3 months, the female worm lays thousands of eggs per day. The parasite can stay in the intetine between 1-5 years. Trichuris trichiura is a parasite of humans, while Trichuris muris is a mouse parasite, used usually as the animal model to study its infection.

In contrast to intracellular pathogens, a Th1 response is non-protective in infection with large extracellular pathogens such as intestinal helminths. For instance, during infection with Trichuris muris, a Th2 response comprising IL-4 and Ig-E production leads to resolution of infection, while a Th1 response comprising IFN-gamma, IL-12 and IL-18 is not protective.

S Hadidi et al. look at regulation of the immune response to T. muris and focus on the importance of the macrophage lipid phosphatase Ship1. Ship1 or Sh-2 containing inositol 5′ phosphatase 1 is a regulator of the PI3K pathway. Hadidi et al. show that Ship1 expression is upregulated steadily following T. muris infection. Ship1-/- mice have higher parasite burden and IFN-gamma while lower levels of IL-13. Also, Ship1-/- macrophages produce more IL-12. Blocking IL-12 or IFN-gamma by blocking antibodies rescued the phenotype by reducing worm burden and increase in IL-13. Thus, they found how activity of this phosphatase can direct the immune response against T. muris infection. It would be very interesting now to see what stimuli induce upregulation of Ship1 and also what are this enzyme’s substrates, which are so important for production of IL-12 by macrophages.

Similar to this story, a few years ago, Abu-Dayyeh et al. and Gomez et al. showed that activating phosphatases is important for Leishmania to establish its infection. Being an intracellular parasite, a Th1 response, with large amounts of IFN-gamma would be protective against Leishmania. So in this context, Leishmania-mediated activation of many phosphatases (most importantly SHP-1) leading to inhibition of IL-12 production leads to disease progression, because it skews the immune response towards Th2. In this situation, Leishmania takes advantage of the phosphatase’s function.

Hadidi S, Antignano F, Hughes MR, Wang SK, Snyder K, Sammis GM, Kerr WG, McNagny KM, & Zaph C (2012). Myeloid cell-specific expression of Ship1 regulates IL-12 production and immunity to helminth infection. Mucosal immunology, 5 (5), 535-43 PMID: 22535180

Abu-Dayyeh I, Shio MT, Sato S, Akira S, Cousineau B, & Olivier M (2008). Leishmania-induced IRAK-1 inactivation is mediated by SHP-1 interacting with an evolutionarily conserved KTIM motif. PLoS neglected tropical diseases, 2 (12) PMID: 19104650
Gomez MA, Contreras I, Hallé M, Tremblay ML, McMaster RW, & Olivier M (2009). Leishmania GP63 alters host signaling through cleavage-activated protein tyrosine phosphatases. Science signaling, 2 (90) PMID: 19797268
ResearchBlogging.org

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Can KTIM be a regulatory site widely used by cytosolic kinases?

Identification of Key Cytosolic Kinases Containing Evolutionarily Conserved Kinase Tyrosine-based Inhibitory Motifs (KTIMs).

Posted by: Issa Abu-Dayyeh

I have posted an earlier article to talk about our PLoS NTD paper where we have described a novel strategy by which Leishmania was able to inhibit TLR-mediated macrophage activation through its ability to inhibit IRAK-1 kinase activity by activating the protein tyrosine phosphatase  (PTP) SHP-1.

We have identified the site of binding between SHP-1 and IRAK-1 to be an evolutionarily conserved ITIM-like motif, which we called a kinase tyrosine-based inhibitory motif (KTIM). In this newly-published paper in Developmental and Comparative Immunology, Abu-Dayyeh et al. present evolutinary as well as experimental data that propose that KTIMs could potentially represent a novel regulatory site involved in the control of the kinase activity of many key kinases involved in siganlling pathways of immune cells. Although this work awaits to be further explored by other researches, I believe this work could open various doors towards many important discoveries in the field of immunology.

Here is the abstract of the paper:

We previously reported that SHP-1 regulates IRAK-1 activity by binding to an ITIM-like motif found within its kinase domain, which we named Kinase Tyrosine-based Inhibitory Motif (KTIM). Herein, we further investigated the presence, number, location, and evolutionary time of emergence of potential KTIMs in many cytosolic kinases, all known to play important roles in the signalling and function of immune cells. We unveil that several kinases contain potential KTIMs, mostly located within their kinase domain and appearing predominantly at the level of early vertebrates becoming highly conserved thereafter. Regarding the KTIMs that were found conserved in both vertebrates and invertebrates, we provide experimental data suggesting that such motifs may have constituted readily-available sites that performed new regulatory functions as soon as their binding partners (e.g. SHP-1) appeared in vertebrates. We thus propose KTIMs as novel regulatory motifs in kinases that function through binding to SH2 domain-containing proteins such as SHP-1. Copyright © 2009. Published by Elsevier Ltd.

PMID: 20043942

doi:10.1016/j.dci.2009.12.012

We know Nirtic Oxide is produced when SHP-1 is absent, but why??

Posted by: Issa Abu-Dayyeh

The exact role played by the protein tyrosine phosphatase (SHP-1) in the negative regulation of macrophage functions has been an active area of research for many years. In fact, SHP-1 deficient mice are hyper-inflammatory. They lose their hair “for God’s sake” due to exaggerated inflammatory responses in the skin area! (hence their name motheaten). But what does this tell us? It tells us a lot of pathways are simply “on fire”. To dissect every single pathway controlled by this PTP is a humongous job, and the best approach in my opinion is to try to focus, and dissect a pathway at a time and a function at a time. So, what did we attempt to do in our most recent publication (Blanchette, J. et al.) in Immunology (2008)?

The paper explores the signaling pathways that seem to be major contributors to NO production in SHP-1 deficient macrophages. NO production is driven by a gene known as iNOS whose expression is driven by several transcription factors, most importantly: Nf-kB, STAT, and AP-1. One of those transcription factors “AP-1” is activated by a MAP kinase called JNK.

This work utilizes inhibitors of many of these members to see which of them will be able to suppress that excess NO production observed in SHP-1 deficient macrophages in an effort to understand how SHP-1 causes this increased NO production.

To save you the dull experimental details…Results showed that the exaggerated NO production in SHP-1-/- macrophages seems to be due to an increased JNK/AP-1 and not NF-kB activity.

And so what? some people might ask!

Well…I agree a finding like this might not find a cure to leishmaniasis. Nevertheless, bearing in mind that NF-kB translocation is increased in the absence of SHP-1, this paper then suggests something rather important. This increased NF-kB activity is not contributing to iNOS transcription. What is it doing then? and how can iNOS be differentially regulated? These are questions that await answers. (If somebody has answers, I will be glad to hear from them).

This work simply broadens our knowledge about where SHP-1 exerts its effects, and by knowing how, we can probably try to eventually revert some of those actions during the course of a Leishmania infection and help find an effective drug against leishmaniasis that is not as toxic as the ones available nowadays…

A block added to the wall. that is how I see it.

If you are interested in viewing the paper, please visit it here

Enjoy,

Issa