The role of microsporidian polar tube protein 4 (PTP4) in host cell infection

Abstract

Microsporidia have been identified as pathogens that have important effects on our health, food security and economy. A key to the success of these obligate intracellular pathogens is their unique invasion organelle, the polar tube, which delivers the nucleus containing sporoplasm into host cells during invasion. Due to the size of the polar tube, the rapidity of polar tube discharge and sporoplasm passage, and the absence of genetic techniques for the manipulation of microsporidia, study of this organelle has been difficult and there is relatively little known regarding polar tube formation and the function of the proteins making up this structure. Herein, we have characterized polar tube protein 4 (PTP4) from the microsporidium Encephalitozoon hellem and found that a monoclonal antibody to PTP4 labels the tip of the polar tube suggesting that PTP4 might be involved in a direct interaction with host cell proteins during invasion. Further analyses employing indirect immunofluorescence (IFA), enzyme-linked immunosorbent (ELISA) and fluorescence-activated cell sorting (FACS) assays confirmed that PTP4 binds to mammalian cells. The addition of either recombinant PTP4 protein or anti-PTP4 antibody reduced microsporidian infection of its host cells in vitro. Proteomic analysis of PTP4 bound to host cell membranes purified by immunoprecipitation identified transferrin receptor 1 (TfR1) as a potential host cell interacting partner for PTP4. Additional experiments revealed that knocking out TfR1, adding TfR1 recombinant protein into cell culture, or adding anti-TfR1 antibody into cell culture significantly reduced microsporidian infection rates. These results indicate that PTP4 is an important protein competent of the polar tube involved in the mechanism of host cell infection utilized by these pathogens.

Morphology and Transcriptome Analysis of Nosema bombycis Sporoplasm and Insights into the Initial Infection of Microsporidia

“…Microsporidia may invade host cells by a variety of means. The main hypotheses include direct penetration of the host cell through the polar tube, polar tube interaction with the host cell plasma membrane and sporoplasm endocytosis, and spore adher-ence to the host cell and invasion by endocytosis (12,37,38). However, the molecular mechanism of these invasion methods is unknown, and the role that the sporoplasm plays in the infection process has not been widely reported.…”

“…Microsporidia can survive in the external environment as highly resistant spores with a thick two-layered wall, and they contain a highly specialized invasion apparatus called the polar tube used to release sporoplasm (3,(10)(11)(12). After the successful transfer of sporoplasm into the host cell cytoplasm, the infective sporoplasm enters the proliferative stage and completes the life cycle (11,13).…”

Natural variation in the roles of C. elegans autophagy components during microsporidia infection

“…Our observations that lgg-2 controls sporoplasm levels at both 15 minutes post-inoculation and 3 hpi are arguably the earliest stages at which a host factor has been shown to control microsporidia load in any system. Studies of microsporidia species that infect mammalian cells have implicated host glycosaminoglycans 44 and a transferrin receptor protein 45 in regulation of early steps, but the exact stage and mechanism by which they act is unknown. It will be interesting to further explore this early role for lgg-2 to shed light on the poorly understood question of how hosts control microsporidia infection.…”

Dicer regulates Nosema ceranae proliferation in honeybees

“…Different host genes of the apoptosis pathway were reported to be regulated to inhibit the apoptosis across different parasite species (del Aguila et al ., ; Higes et al ., ; He et al ., ; Doublet et al ., ; Martín‐Hernández et al ., ). Additional studies have tried to identify the important proteins for microsporidian infection, including parasite polar tube proteins, cell wall proteins, adenosine triphosphate transporters and host cuticle proteins (Xu and Weiss, ; Paldi et al ., ; Li et al ., ; ; Han et al ., ). Nevertheless, there have been few attempts to identify more broadly the pathways used by microsporidia to infect hosts, and the counter‐defences hosts might use to reduce the impacts of infection.…”

“…Correspondence: Qiang Huang, Institute of Bee Health, Vetsuisse Faculty, University of Bern, Schwarzenburgstrasse 161, Liebefeld,Switzerland; transporters and host cuticle proteins (Xu and Weiss, 2005;Paldi et al, 2010;Li et al, 2016Li et al, , 2012Han et al, 2017). Nevertheless, there have been few attempts to identify more broadly the pathways used by microsporidia to infect hosts, and the counter-defences hosts might use to reduce the impacts of infection.…”