Identification of a novel interaction between Theileria Prohibitin (TaPHB-1) and bovine RUVBL-1
Authors: Araveti Prasanna Babu , Kar Prajna Parimita , Kuriakose Akshay , Sanju Achintya , Srivastava Anand 
Published: February 2022

Bovine tropical theileriosis causes huge economic loss worldwide. It is a tick borne disease of bovine caused by the parasite Theileria annulata. T. annulata is an intracellular parasite that belongs to the phylum Apicomplexa. The sporozoites of T. annulata are released by the tick into the bloodstream of the host during the blood meal that invades bovine B cells, macrophages, or monocytes. This infection leads to the transformation of the host cells and brings cancer-like phenotype in the host cells. The parasite proteins play a vital role in the transformation of the host cell. However, the parasite factors involved in the host cell transformation are not well explored. Previously, TaPIN1, a peptidyl-prolyl isomerase of T. annulata, was shown to be secreted to the host cytosol and play a role in the host cell transformation. The present study was carried out to explore the parasite-host interactions that may play an important role in the host cell transformation. We identified the parasite proteins that are expressed in the schizont stage with a signal peptide. We narrow down our search to a parasite prohibitin. The in silico analysis of T. annulata prohibitin (TA04375, TaPHB-1) showed that TaPHB-1 shares homology with the mammalian prohibitin 1. With the localization experiments, we confirmed that TaPHB-1 is exported to the parasite surface and also to the host cell cytosol. Further, we observed that the localization of host prohibitin differs in the parasite-infected cells and could not be reverted back by the elimination of the parasite in the infected cells. We found through the yeast-two-hybrid studies that bovine RUVBL1 (BoRUVBL-1) interacts with TaPHB-1. The interaction between BoRUVBL1 and TaPHB-1 was predominantly observed on the parasite surface in the infected bovine cells. The interaction was further confirmed with immunoprecipitation and LC-MS/MS analysis. Further, the LC-MS/MS based TaPHB-1 interactome study reveals that it interacts with proteins that regulate actin cytoskeleton organization, protein folding, mRNA processing, and metabolic processes. Our finding suggests that the parasite releases prohibitin protein into the cytoplasm of the host cell where it interacts with the host RUVBL-1. This finding has implications not only in the understanding of Theileria parasite biology in greater depth but also in the cancer biology where previously differential localization of prohibitin proteins was observed but its interaction partner was not known.

Author summary

Theileria annulata, an apicomplexan, is a unique parasite which can transform host leucocytes. This parasite uses this strategy for its own multiplication. The cells infected with this parasite, when treated with buparvaquone, an anti-theilerial drug, cannot survive without the parasite. This observation suggests that the parasite derived factors are required to maintain the cancerous phenotype of the host cell. We mined the parasite proteome to find out the proteins with signal sequence that may be secreted to the host cell cytosol and being expressed in the schizont stage. The parasite prohibitin (TaPHB-1) chosen for this study was found to be secreted to the host cytoplasm and on the parasite surface. Interestingly, we observed a noticeable change in the localization of the host prohibitin in the parasite infected cells. The host prohibitin that is normally localized to the mitochondria in the uninfected cells was observed in the host cell nucleus similar to the cancerous cells. Since the parasite protein is exported to the host cytoplasm we looked for its interacting partner. We performed yeast-two-hybrid screening with TaPHB-1 with in-house prepared the cDNA library of the infected bovine leucocytes. We identified bovine RUVBL1 as the interacting partner of TaPHB-1. Interestingly, the interaction between parasite prohibitin and bovine RUVBL1 was observed on the parasite surface. Further, analysis of the parasite prohibitin interactome in the infected cells shows that it might be involved with those proteins which regulate actin cytoskeleton organization, protein folding, mRNA processing and metabolic process. Since parasite infected cells have cancer like phenotype, the identification of this novel interaction will open up new avenues not only in the arena of parasite biology but also in the domain of cancer biology.