CCTδ colocalizes with actin and β-tubulin: Insight into its involvement in the cytoskeleton formation of the intracellular parasite Nosema bombycis

Characterization and functional analysis of the small heat shock protein HSP19.5 in Bombyx mori in response to Nosema bombycis infection

Small heat shock proteins (sHSPs) are molecular chaperones known for their role in maintaining cellular homeostasis and protecting cells from various environmental stresses. This study focuses on the silkworm small heat shock protein HSP19.5 and its potential functions in the context of Nosema bombycis infection, a microsporidian pathogen causing severe disease in the sericulture industry. We cloned and characterized HSP19.5 and revealed its expression patterns in different silkworm tissues and developmental stages. Our results indicate that HSP19.5 expression is significantly up-regulated in response to N. bombycis infection, suggesting a role in the host stress response. Through a series of experiments, including RNA interference and overexpression analyses, we demonstrated that HSP19.5 promotes N. bombycis proliferation, possibly by inhibiting host cell apoptosis and regulating intracellular ROS levels. The cytoplasmic localization of HSP19.5 in silkworm cells is consistent with its function as a molecular chaperone. The results enhance our understanding of the complex host-pathogen interactions between silkworms and N. bombycis, and provides insights that may inform the development of novel strategies to control the pebrine disease.

Glucose-regulated protein 78 regulates the subunit-folding of the CCT complex by modulating gene expression and protein interaction in the microsporidian Nosema bombycis

Chaperonin containing tailless complex polypeptide 1 (CCT) functions as a molecular chaperone and is essential for ensuring proper protein folding. Glucose-regulated protein 78 (GRP78/Bip), also a type of chaperone, not only assists in folding of proteins, but also facilitates the transportation of proteins into the endoplasmic reticulum (ER) via the Sec protein complex. In this study, we identified the CCTη of N. bombycis (NbCCTη) for the first time. Immunoprecipitations and mass spectrometry (IP-MS) of NbCCTη analysis showed that NbBip may interact with CCT subunits. Yeast two-hybrid assays validated that NbBip interacts with NbCCTη, as well as NbCCTα and NbCCTε. Furthermore, RNA interference on NbBip brought about radical expression of NbCCTα, NbCCTε, and NbCCTη, while RNAi on NbCCT subunits resulted in abnormal expression of NbBip. Immunofluorescence assay results showed that NbBip colocalized with NbCCTα and NbCCTη, and CCTη colocalized with Nbβ-tubulin and Nbactin in the parasite. Collectively, these findings suggest that NbBip may act as a crucial factor in the subunit-folding and assembly of CCT complex in N. bombycis.

Ssn6 Interacts with Polar Tube Protein 2 and Transcriptional Repressor for RNA Polymerase II: Insight into Its Involvement in the Biological Process of Microsporidium Nosema bombycis

Nosema bombycis is a representative species of Microsporidia, and is the pathogen that causes pebrine disease in silkworms. In the process of infection, the polar tube of N. bombycis is injected into the host cells. During proliferation, N. bombycis recruits the mitochondria of host cells. The general transcriptional corepressor Ssn6 contains six tetratricopeptide repeats (TPR) and undertakes various important functions. In this study, we isolated and characterized Nbssn6 of the microsporidium N. bombycis. The Nbssn6 gene contains a complete ORF of 1182 bp in length that encodes a 393 amino acid polypeptide. Indirect immunofluorescence assay showed that the Ssn6 protein was mainly distributed in the cytoplasm and nucleus at the proliferative phase of N. bombycis. We revealed the interaction of Nbssn6 with polar tube protein 2 (Nbptp2) and the transcriptional repressor for RNA polymerase II (Nbtrrp2) by Co-IP and yeast two-hybrid assays. Results from RNA interference further confirmed that the transcriptional level of Nbptp2 and Nbtrrp2 was regulated by Nbssn6. These results suggest that Nbssn6 impacts the infection and proliferation of N. bombycis via interacting with the polar tube protein and transcriptional repressor for RNA polymerase II.

Identification and subcellular localization analysis of CCTα in microsporidian Nosema bombycis

CCT is a chaperonin which is widely present in eukaryotic cells and mainly involves in the folding and assembly of cytoskeletal proteins β-tubulin and actin. The alpha subunit of CCT(CCTα) plays a pivotal role in the folding and assembly of cytoskeletal protein(s) as an individuals or complexes. In this study, we report cloning, characterization and expression of the CCTα of Nosema bombycis (NbCCTα) for the first time. The NbCCTα gene contains a complete ORF of 1629 bp in length that encodes a 542-amino acid polypeptide. The NbCCTα is 59.662 kDa molecular weight in size with an isoelectric point (pI) of 5.81, no signal peptide or transmembrane domain. The IFA results showed that the NbCCTα was co-localized with actin and β-tubulin in the cytoplasm, nucleus, nuclear membrane and plasma membrane of N. bombycis in the process of proliferation. qPCR analysis showed that the relative expression level of NbCCTα increased from 24 h to 96 h post-infection (hp.i) of N. bombycis, and reached the highest at 96 hp.i. The relative expression level of NbCCTα gene after RNAi was restrained at a low level from 48 hp.i to 96 hp.i. Knockdown of NbCCTα gene down-regulated the expression of Nbβ-tubulin and Nbactin genes. These results imply that NbCCTα may play an important role in the lifecycle of N. bombycis.

Identification and subcellular localization analysis of membrane protein Ycf 1 in the microsporidian Nosema bombycis

Microsporidia are obligate intracellular parasites that can infect a wide range of vertebrates and invertebrates including humans and insects, such as silkworm and bees. The microsporidium Nosema bombycis can cause pebrine in Bombyx mori, which is the most destructive disease in the sericulture industry. Although membrane proteins are involved in a wide range of cellular functions and part of many important metabolic pathways, there are rare reports about the membrane proteins of microsporidia up to now. We screened a putative membrane protein Ycf 1 from the midgut transcriptome of the N. bombycis-infected silkworm. Gene cloning and bioinformatics analysis showed that the Ycf 1 gene contains a complete open reading frame (ORF) of 969 bp in length encoding a 322 amino acid polypeptide that has one signal peptide and one transmembrane domain. Indirect immunofluorescence results showed that Ycf 1 protein is distributed on the plasma membrane. Expression pattern analysis showed that the Ycf 1 gene expressed in all developmental stages of N. bombycis. Knockdown of the Ycf 1 gene by RNAi effectively inhibited the proliferation of N. bombycis. These results indicated that Ycf 1 is a membrane protein and plays an important role in the life cycle of N. bombycis.