Identification and characterization of an insect homologue of the vertebrate Golgi apparatus protein 1 (MG-160/cysteine-rich fibroblast growth factor receptor/E-selectin ligand-1/latent transforming growth factor-beta complex protein-1) with a Golgi-specific monoclonal antibody

Impact of Hypermannosylation on the Structure and Functionality of the ER and the Golgi Complex

Proteins of the secretory pathway undergo glycosylation in the endoplasmic reticulum (ER) and the Golgi apparatus. Altered protein glycosylation can manifest in serious, sometimes fatal malfunctions. We recently showed that mutations in GDP-mannose pyrophosphorylase A (GMPPA) can cause a syndrome characterized by alacrima, achalasia, mental retardation, and myopathic alterations (AAMR syndrome). GMPPA acts as a feedback inhibitor of GDP-mannose pyrophosphorylase B (GMPPB), which provides GDP-mannose as a substrate for protein glycosylation. Loss of GMPPA thus enhances the incorporation of mannose into glycochains of various proteins, including α-dystroglycan (α-DG), a protein that links the extracellular matrix with the cytoskeleton. Here, we further characterized the consequences of loss of GMPPA for the secretory pathway. This includes a fragmentation of the Golgi apparatus, which comes along with a regulation of the abundance of several ER- and Golgi-resident proteins. We further show that the activity of the Golgi-associated endoprotease furin is reduced. Moreover, the fraction of α-DG, which is retained in the ER, is increased. Notably, WT cells cultured at a high mannose concentration display similar changes with increased retention of α-DG, altered structure of the Golgi apparatus, and a decrease in furin activity. In summary, our data underline the importance of a balanced mannose homeostasis for the secretory pathway.

The invasive cell coat at the microsporidian Trachipleistophora hominis-host cell interface contains secreted hexokinases

Microsporidia are obligate intracellular parasites causing significant disease in humans and economically important animals. In parallel to their extreme genetic reduction, Microsporidia have evolved novel mechanisms for exploiting host metabolism. A number of microsporidians confer secretion of otherwise cytosolic proteins by coding for signal peptides that direct entry into the endoplasmic reticulum. The human pathogen Trachipleistophora hominis encodes for four hexokinases, three of which have signal peptides at the N‐terminus. Here, we localized hexokinase 2 and hexokinase 3 through developmental stages of T. hominis using light and electron microscopy. Both proteins were concentrated in an extracellular coat previously termed the plaque matrix (PQM). The PQM (containing hexokinases) was morphologically dynamic, infiltrating the host cytoplasm predominantly during replicative stages. Throughout development the PQM interacted closely with endoplasmic reticulum that was demonstrated to be active in membrane protein biosynthesis and export. The impact of hexokinase on the host metabolism was probed using the fluorescent analog of glucose, 2‐NBDG, which displayed spatially restricted increases in signal intensity at the parasite/vacuole surface, coincident with hexokinase/PQM distribution. Gross metabolic aberrations, measured using metabolic profiling with the Seahorse XF Analyzer, were not detectable in mixed stage cocultures. Overall, these results highlight a role for the extended cell coat of T. hominis in host–parasite interactions, within which secreted hexokinases may work as part of a metabolic machine to increase glycolytic capacity or ATP generation close to the parasite surface.

Transcriptional response of a common permissive cell type to infection by two diverse alphaherpesviruses

Pseudorabies virus (PRV) and herpes simplex virus type 1 (HSV-1) are distantly related alphaherpesviruses whose natural hosts are pigs and humans, respectively. Adult infections of natural hosts are mild and rarely lethal. However, both viruses are also able to infect other hosts, often with lethal effects. In this report, we use the paradigm of infection of a common permissive cell type and microarray analysis to determine if these two diverse alphaherpesviruses engage similar or different cellular pathways to obtain a common outcome: productive infection. We compared cellular gene expression in growth-arrested, primary rat embryonic fibroblasts that were mock infected or infected with either purified PRV-Becker or HSV-1(F). Infections by either virus affect the transcription of more than 1,500 cellular genes by threefold or more. Few differences are detected early, and the majority of changes occur during the late stages of infection. Remarkably, the transcripts of about 500 genes are regulated in common, while the rest are regulated in a virus-specific manner. Genes whose expression is affected by infection fall into a diverse group of functional classes and cellular pathways. Furthermore, a comparison of the cellular response to HSV-1 infection of primary human and rat fibroblasts revealed unexpected diversity in the transcript profiles.

Progress in focus: recent advances in histochemistry and cell biology

Advances in histochemical and cell biological techniques enable increasingly refined investigations into the cellular and subcellular distribution of specific molecules and into their role in dynamic processes; thus progress in these fields complements the growing knowledge in genomics and proteomics. The present review summarizes recent technical progress and novel applications.