Dok proteins are recruited to the phagosome and degraded in a GP63-dependent manner during Leishmania major infection

Introduction to DOK2 and its potential role in cancer

Cancer is a complex, multifactorial disease that modern medicine ultimately aims to overcome. Downstream of tyrosine kinase 2 (DOK2) is a well-known tumor suppressor gene, and a member of the downstream protein DOK family of tyrosine kinases. Through a search of original literature indexed in PubMed and other databases, the present review aims to extricate the mechanisms by which DOK2 acts on cancer, thereby identifying more reliable and effective therapeutic targets to promote enhanced methods of cancer prevention and treatment. The review focuses on the role of DOK2 in multiple tumor types in the lungs, intestines, liver, and breast. Additionally, we discuss the potential mechanisms of action of DOK2 and the downstream consequences via the Ras/MPAK/ERK or PI3K/AKT/mTOR signaling pathways.

Construction of PX-LmGP63 Using CRISPR-Cas9 as Primary Goal for GP63 gene Knockout in Leishmania major and Leishmanization

Background: Leishmania is an intracellular protozoan parasite that uses complex methods for destroying the innate immune response in mammalian host macrophage cells. Many factors have been identified that play a role in the severity of the parasite’s pathogenicity. One of the factors is the GP63, which is a group of metalloproteinases that disrupts the signaling mechanism of the host cell. Objectives: The aim of this study was to construct PX-LMGP63 vector through CRISPR-Cas9 for GP63 gene knockout in Leishmania major as a potential method for leishmanization. Methods: A pair of gRNAs were designed based on the mRNA sequence of the GP63. Then annealing primers were cloned into the linearized vector PX-459 and transformed into the DH5ɑ competent cells. Then, PCR assay was performed with gene-specific and vector primers to confirm the colonies. In addition, the constructed plasmid was sequenced for final confirmation. Results: The expected size band of 270 was confirmed by PCR. The plasmid sequence showed that the gRNA789 was ligated in the vector. The created structure was named PX-LMGP63 and will be transfected into the promastigote cell in the next step. Conclusions: Owing to the prevalence of cutaneous Leishman as a public health problem in most countries and the lack of an effective vaccine for leishmaniasis, the use of the CRISPR method may make it possible to achieve an effective vaccine in the future.

Leishmania Hijacks Myeloid Cells for Immune Escape

Protozoan parasites of the Leishmania genus are the causative agents of leishmaniasis, a group of neglected tropical diseases whose clinical manifestations vary depending on the infectious Leishmania species but also on host factors. Recognition of the parasite by host myeloid immune cells is a key to trigger an effective Leishmania-specific immunity. However, the parasite is able to persist in host myeloid cells by evading, delaying and manipulating host immunity in order to escape host resistance and ensure its transmission. Neutrophils are first in infiltrating infection sites and could act either favoring or protecting against infection, depending on factors such as the genetic background of the host or the parasite species. Macrophages are the main host cells where the parasites grow and divide. However, macrophages are also the main effector population involved in parasite clearance. Parasite elimination by macrophages requires the priming and development of an effector Th1 adaptive immunity driven by specific subtypes of dendritic cells. Herein, we will provide a comprehensive outline of how myeloid cells regulate innate and adaptive immunity against Leishmania, and the mechanisms used by the parasites to promote their evasion and sabotage. Understanding the interactions between Leishmania and the host myeloid cells may lead to the development of new therapeutic approaches and improved vaccination to leishmaniases, an important worldwide health problem in which current therapeutic or preventive approaches are limited.

Moesin and myosin IIA modulate phagolysosomal biogenesis in macrophages

Biogenesis of phagolysosomes is central to the elimination of pathogens by macrophages. We previously showed that Src homology region 2 domain-containing phosphatase 1 (SHP-1) participates in the regulation of phagosome maturation. Through proteomics, we identified moesin and the non-muscle myosin-IIA as proteins interacting with SHP-1 during phagocytosis. Silencing of either moesin or myosin IIA with small interfering RNA inhibited phagosomal acidification and recruitment of LAMP-1. Moreover, the intraphagosomal oxidative burst was impaired in the absence of either SHP-1 or myosin IIA but not moesin. Finally, absence of either SHP-1, moesin, or myosin IIA ablated the capacity of macrophages to clear bacterial infection. Collectively, these results implicate both moesin and myosin IIA in the regulation of phagolysosome biogenesis and in host defense against infections.

Dok-1 and Dok-2 Are Required To Maintain Herpes Simplex Virus 1-Specific CD8+ T Cells in a Murine Model of Ocular Infection

Dok-1 and Dok-2 negatively regulate responses downstream of several immune receptors in lymphoid and myeloid cells. Recent evidence showed that Dok proteins are essential in the formation of memory CD8⁺ T cells to an exogenous epitope expressed by vaccinia virus; however, the importance of Dok-1 and Dok-2 in the control of viral infection is unknown. Here, we investigated the role of Dok proteins in modulating the immune response against herpes simplex virus 1 (HSV-1) in a mouse model of ocular infection. During acute infection, viral titers in the eye were similar in wild-type (WT) and Dok-1 and Dok-2 double-knockout (DKO) mice, and the percentages of infiltrating leukocytes were similar in DKO and WT corneas and trigeminal ganglia (TG). DKO mice exhibited a diminished CD8⁺ T cell response to the immunodominant HSV-1 glycoprotein B (gB) epitope in the spleen and draining lymph nodes compared to WT mice during acute infection. Remarkably, gB-specific CD8⁺ T cells almost completely disappeared in the spleens of DKO mice during latency, and the reduction of CD8⁺ effector memory T (Tem) cells was more severe than that of CD8⁺ central memory T (Tcm) cells. The percentage of gB-specific CD8⁺ T cells in TG during latency was also dramatically reduced in DKO mice; however, they were phenotypically similar to those from WT mice. In ex vivo assays, reactivation was detected earlier in TG cultures from infected DKO versus WT mice. Thus, Dok-1 and Dok-2 promote survival of gB-specific CD8⁺ T cells in TG latently infected with HSV-1.IMPORTANCE HSV-1 establishes lifelong latency in sensory neurons of trigeminal ganglia (TG). In humans, HSV-1 is able to sporadically reactivate from latently infected neurons and establish a lytic infection at a site to which the neurons project. Most herpetic disease in humans is due to reactivation of HSV-1 from latency rather than to primary acute infection. CD8⁺ T cells are thought to play an important role in controlling recurrent infections. In this study, we examined the involvement of Dok-1 and Dok-2 signaling proteins in the control of HSV-1 infection. We provide evidence that Dok proteins are required to maintain a CD8⁺ T cell response against HSV-1 during latency-especially CD8⁺ Tem cells-and that they negatively affect HSV-1 reactivation from latency. Elucidating Dok-mediated mechanisms involved in the control of HSV-1 reactivation from latency might contribute to the development of therapeutic strategies to prevent recurrent HSV-1-induced pathology.

Leishmania major Promastigotes Evade LC3-Associated Phagocytosis through the Action of GP63

The protozoan Leishmania parasitizes macrophages and evades the microbicidal consequences of phagocytosis through the inhibition of phagolysosome biogenesis. In this study, we investigated the impact of this parasite on LC3-associated phagocytosis, a non-canonical autophagic process that enhances phagosome maturation and functions. We show that whereas internalization of L. major promastigotes by macrophages promoted LC3 lipidation, recruitment of LC3 to phagosomes was inhibited through the action of the parasite surface metalloprotease GP63. Reactive oxygen species generated by the NOX2 NADPH oxidase are necessary for LC3-associated phagocytosis. We found that L. major promastigotes prevented, in a GP63-dependent manner, the recruitment of NOX2 to phagosomes through a mechanism that does not involve NOX2 cleavage. Moreover, we found that the SNARE protein VAMP8, which regulates phagosomal assembly of the NADPH oxidase NOX2, was down-modulated by GP63. In the absence of VAMP8, recruitment of LC3 to phagosomes containing GP63-deficient parasites was inhibited, indicating that VAMP8 is involved in the phagosomal recruitment of LC3. These findings reveal a role for VAMP8 in LC3-associated phagocytosis and highlight a novel mechanism exploited by L. major promastigotes to interfere with the host antimicrobial machinery.

The early events surrounding and following the phagocytosis of pathogens largely determine whether internalization will lead to efficient killing of the microbe or successful establishment of an intracellular infection. Growing evidence supports the notion that the autophagy machinery lends a hand to phagocytosis in eliminating intracellular pathogens, in a process known as LC3-associated phagocytosis (LAP). Protozoan parasites of the Leishmania genus use surface virulence factors such as lipophosphoglycan and the metalloprotease GP63 to interfere with phagolysosome biogenesis and sabotage macrophage antimicrobial functions. Here, we provide the first evidence that L. major promastigotes evade LAP in a GP63-dependent manner and uncover a novel role for the membrane fusion mediator VAMP8 in LAP. Our findings offer a better understanding of Leishmania pathogenesis and of the mechanism behind LAP.

Leishmania hijacking of the macrophage intracellular compartments

Leishmania spp., transmitted to humans by the bite of the sandfly vector, are responsible for the three major forms of leishmaniasis, cutaneous, diffuse mucocutaneous and visceral. Leishmania spp. interact with membrane receptors of neutrophils and macrophages. In macrophages, the parasite is internalized within a parasitophorous vacuole and engages in a particular intracellular lifestyle in which the flagellated, motile Leishmania promastigote metacyclic form differentiates into non-motile, metacyclic amastigote form. This phenomenon is induced by Leishmania-triggered events leading to the fusion of the parasitophorous vacuole with vesicular members of the host cell endocytic pathway including recycling endosomes, late endosomes and the endoplasmic reticulum. Maturation of the parasitophorous vacuole leads to the intracellular proliferation of the Leishmania amastigote forms by acquisition of host cell nutrients while escaping host defense responses.

Leishmania survival in the macrophage: where the ends justify the means

Macrophages are cells of the immune system that mediate processes ranging from phagocytosis to tissue homeostasis. Leishmania has evolved ingenious ways to adapt to life in the macrophage. The GP63 metalloprotease, which disables key microbicidal pathways, has recently been found to disrupt processes ranging from antigen cross-presentation to nuclear pore dynamics. New studies have also revealed that Leishmania sabotages key metabolic and signaling pathways to fuel parasite growth. Leishmania has also been found to induce DNA methylation to turn off genes controlling microbicidal pathways. These novel findings highlight the multipronged attack employed by Leishmania to subvert macrophage function.