A novel progesterone receptor membrane component (PGRMC) in the human and swine parasite Taenia solium: implications to the host-parasite relationship

Abstract

Background: We have previously reported that progesterone (P₄) has a direct in vitro effect on the scolex evagination and growth of Taenia solium cysticerci. Here, we explored the hypothesis that the P₄ direct effect on T. solium might be mediated by a novel steroid-binding parasite protein.

Methods: By way of using immunofluorescent confocal microscopy, flow cytometry analysis, double-dimension electrophoresis analysis, and sequencing the corresponding protein spot, we detected a novel PGRMC in T. solium. Molecular modeling studies accompanied by computer docking using the sequenced protein, together with phylogenetic analysis and sequence alignment clearly demonstrated that T. solium PGRMC is from parasite origin.

Results: Our results show that P₄ in vitro increases parasite evagination and scolex size. Using immunofluorescent confocal microscopy, we detected that parasite cells showed expression of a P₄-binding like protein exclusively located at the cysticercus subtegumental tissue. Presence of the P₄-binding protein in cyst cells was also confirmed by flow cytometry. Double-dimension electrophoresis analysis, followed by sequencing the corresponding protein spot, revealed a protein that was previously reported in the T. solium genome belonging to a membrane-associated progesterone receptor component (PGRMC). Molecular modeling studies accompanied by computer docking using the sequenced protein showed that PGRMC is potentially able to bind steroid hormones such as progesterone, estradiol, testosterone and dihydrodrotestosterone with different affinities. Phylogenetic analysis and sequence alignment clearly demonstrated that T. solium PGRMC is related to a steroid-binding protein of Echinoccocus granulosus, both of them being nested within a cluster including similar proteins present in platyhelminths such as Schistocephalus solidus and Schistosoma haematobium.

Conclusion: Progesterone may directly act upon T. solium cysticerci probably by binding to PGRMC. This research has implications in the field of host-parasite co-evolution as well as the sex-associated susceptibility to this infection. In a more practical matter, present results may contribute to the molecular design of new drugs with anti-parasite actions.

Keywords: Cysticerci; Helminth; Hormone receptors; PGRMC; Parasite; Progesterone; Taenia solium.

Fig. 1

Photographs of Taenia solium cysticerci in culture. Control cysticerci evaginated after 5 days in culture (C) and cysticerci evaginated after 5 days in culture in the presence of 40 ng of progesterone (P₄)

Fig. 2

Specific detection of the progesterone-binding protein in Taenia solium cysticerci by flow cytometry. FACS analysis in T. solium cysticercus cells showed the PGRMC expression. In untreated cysticerci used as controls, very few cells presented a low immuno-fluorescent signal, whereas P₄-treated cysticerci showed few cells with high immunofluorescent signal related to the receptor expressed in the parasite. a Size and complexity of T. solium cells. b PGRMC expression on T. solium cells. c PGRMC expression on T. solium cells after P₄ stimulation. Solid lines show un-stained cells in all cases. Dotted lines correspond to unspecific staining of the secondary antibody and long-dashed lines correspond to the specific staining of PGRMC

Fig. 3

Progesterone-binding membrane protein location in Taenia solium cysticerci by immunofluorescence. a Representative transversal sections of T. solium cysticerci where tegument, sub-tegument and cells are observed with optical microscopy illumination (Nomarski microscopy). b Negative control of immunofluorescence using the secondary antibody. c Specific detection of progesterone binding membrane protein in parasite (arrows) cells mainly located all along subtegumental tissue (magnification of 100×). d Detail of c showing T. solium cells expressing PGRMC exclusively on subtegument cells (arrows) at higher magnification (400×) from shows in. Abbreviations: T, tegumental cells; GL, germinal layer. Scale-bars: a, 10 μm; b, 10 μm; c, 10 μm; d,10 μm; e, 10 μm; f, 10 μm

Fig. 4

Taenia solium PGRMC characterization by 2D–E. a A representative 2D-E gel showing the location of the protein spot selected for sequencing (red ellipse). b Sequence obtained from protein spot by MALDI-TOF and used in further molecular analysis

Fig. 5

The hydrophilic segment model of PGRMC. The structure is represented as cartoons with N-terminus in blue and the C-terminus in red. In a the cavities are represented as surfaces in the progesterone docking, b shows docking of testosterone, c dehydroepiandrosterone, and d arachidonic acid, all of them in a CPK representation. Note that both dehydroepiandrosterone and arachidonic acid bind to a similar site whereas progesterone binds closer to the C-terminus

Fig. 6

Neighbor-joining tree (NJT) inferred from a dataset composed of 133 characters and with 21 taxa. PGRMCs from several species of fish, amphibians, reptilians, birds and mammals were analyzed through a NJT for searching probable relationship with the T. solium PGRMC identified and sequenced. Numbers near internal nodes show bootstrap replicates