Structural and developmental expression of Ss-riok-2, an RIO protein kinase encoding gene of Strongyloides stercoralis

Wei-Qiang Lei,Wang Yuan,Min Hu,Huan Zhou,Jun-Long Zhao,Si-Yuan He,Rui Zhou,Robin B Gasser,Yue-Zhou Zhang,Jonathan D Stoltzfus,James B Lok

doi:10.1038/s41598-017-07991-2

Abstract

RIO kinases are essential atypical protein kinases in diverse prokaryotic and eukaryotic organisms, playing significant roles in yeast and humans. However, little is known about their functions in parasitic nematodes. In the present study, we have isolated and characterized the full-length cDNA, gDNA and a putative promoter of a RIOK-2 protein kinase (Ss-RIOK-2) encoding gene (Ss-riok-2) from Strongyloides stercoralis, a medically important parasitic nematode (Order Rhabditida). A three-dimensional structure (3D) model of Ss-RIOK-2 was generated using the Chaetomium thermophilum RIOK-2 protein kinase (Ct-RIOK-2) crystal structure 4GYG as a template. A docking study revealed some critical sites for ATP binding and metal binding. The putative promoter of Ss-riok-2 contains a number of conserved elements. RNAseq analysis revealed the highest levels of the Ss-riok-2 transcript in free-living females and parasitic females. To identify anatomical patterns of Ss-riok-2 expression in S. stercoralis, we observed expression patterns of a transgene construct encoding green fluorescent protein under the Ss-riok-2 promoter in post free-living S. stercoralis. Expression driven by this promoter predominated in intestinal cells. This study demonstrates significant advancement in molecular and cellular biological study of S. stercoralis and of parasitic nematodes generally, and provides a foundation for further functional genomic studies.

Highlights

In yeast, RIOK-2 occurs in both the nucleus and cytoplasm[4]
Comparison of Ss-RIOK-2 with its homologues showed that Ss-RIOK-2 has significant similarities to RIOK-2s from a range of organisms, including three nematodes (L. loa; C. elegans; H. contortus) and six other organisms (A. florea; H. sapiens; D. rerio; C. familiaris; A. fulgidus; S. cerevisiae)
To obtain the structural details and arrangement of these domains within Ss-RIOK-2 protein kinase, we modeled the structure of the Ss-RIOK-2 protein kinase using crystal structure of C. thermophilum RIOK-2 (Ct-RIOK-2) kinase as a template (PDB accession number 4GYG)

Summary

Introduction

RIOK-2 occurs in both the nucleus and cytoplasm[4]. In human cells, RIOK-2 (hRIOK-2) localizes to the cytoplasm of cells at steady state but rapidly accumulates in the nucleus when the exportin CRM1 (chromosome region maintenance 1) protein is inhibited by leptomycin B6. RIOK-2 has an important function in ribosome biogenesis after nuclear export In both yeast and human cells, RIOK-2 is a non-ribosomal factor necessary for processing the 18 S precursor ribosomal RNA (pre-rRNA) and for cytoplasmic maturation of the 40 S ribosomal subunit. In human HeLa cells, phosphorylation of RIOK-2 by PLK-1 (Polo-like Kinase 1, encoding an essential gene in the maintenance of the mitotic progression) at Ser-335, Ser-380 and Ser-548 regulated the programmed transition of the cell cycle from metaphase to anaphase. In glioblastoma cells, over-expression of RIOK-2 can promote tumorigenesis by acting upstream of Akt signaling to stimulate Tor-complex-2 (TORC2) signaling[17] This suggests that RIOK-2 may have crucial but different functions in complex signaling events in diverse cells to regulate the entire cell-cycle. The primary objective of this study was to uncover clues to the function of Ss-riok-2 with an eye to deducing its role in the biology of Strongyloides spp

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Conclusion