Targeting of endoplasmic reticulum-associated proteins to axons and dendrites in rotavirus-infected neurons

Abstract

To analyze sorting and compartmentalization of molecules in neuronal endomembranes, the distribution of endogenous proteins associated with the endoplasmic reticulum (ER), intermediate compartment, the Golgi apparatus in cultures of dorsal root ganglion (DRG), and hippocampal neurons was compared with that of newly synthesized ER-associated rotavirus proteins. The endogenous ER-retained immunoglobulin heavy chain binding protein, protein disulfide isomerase, and a peptide containing the KDEL amino acid sequence appeared in the soma and dendrites up to their first branching, but not in axons. However, two other endogenous ER-associated proteins, calreticulin and calnexin, occurred in axons as well as in the somatodendritic domains. The ER-associated rotavirus proteins, VP7 and NSP4, were widely distributed in cell bodies and dendrites. The former appeared also in axons and its localization partially overlapped with that of calreticulin and calnexin. One intermediate compartment protein, ER-Golgi-intermediate compartment-protein-53 (ERGIC-53), extended beyond the first division of the dendrites and did not, as the small guanosine 5'-triphosphate (GTP)-binding protein rab2, appear in axons. The location of rab2 to small vesicles was distinct from that of rotavirus VP7. Cis/medial Golgi cistern proteins were restricted to the cell bodies and proximal dendrites. This study emphasizes the marked heterogeneity in the targeting to axons and dendrites of proteins associated with ER and intermediate compartments. Therefore, the composition of axonal ER-retained molecules differs from that in the soma and this variation may reflect differences in functions between the ER compartments. Viral proteins are useful reporters for such heterogeneities and rotavirus VP7 may be a tool to reveal sorting signals for targeting of vesicular proteins to axons via a nonclassical Golgi-independent mechanism. Such signals may also determine viral targeting to different regions of the brain.

NSP4 Enterotoxin of Rotavirus Induces Paracellular Leakage in Polarized Epithelial Cells

“…Several endogenous proteins and rotavirus VP7 are also mistargeted in neurons infected with rotavirus (44)(45)(46), which further supports the proposal that rotavirus interferes with the secretory pathway. In this work, we found that rotavirus not only prevented lateral targeting of the ZO-1 protein to tight junctions during biogenesis but showed, more importantly, that this novel effect could be associated with NSP4.…”

Synaptic vesicle proteins under conditions of rest and activation: Analysis by 2-D difference gel electrophoresis

“…Rab2 plays an important role in the early secretory pathway and associates with vesiculartubular clusters (VTCs) [38,39]. Besides its ER-Golgilocalisation, rab2 has been identified in axons and dendrites [40]. Rab2-generated retrograde-directed vesicles might use microtubules as tracks for transportation [41].…”

Differential Vesicular Targeting and Time Course of Synaptic Secretion of the Mammalian Neurotrophins

“…As an ER marker, we chose an antibody directed against the ER transmembrane chaperone calnexin, which assists in folding of glycosylated proteins (such as NTs) destined for the Golgi and which has been shown previously to stain rough as well as smooth ER in soma and dendrites of hippocampal neurons (Krijnse-Locker et al, 1995;Weclewicz et al, 1998;Horton and Ehlers, 2003). Cells that displayed the proximal expression pattern showed clear colocalization of calnexin and the respective NT in the soma and additional colocalization of the diffuse NT signals in dendrites with the calnexin staining (Fig.…”