A simple and inexpensive approach to interfacing high-performance liquid chromatography and matrix-assisted laser desorption/ionization-time of flight-mass spectrometry

The ability to obtain the accurate mass of a protein in a complex sample mixture aids in determining its correct in vivo form. This is important when identifying post-translationally modified proteins, protein variants or isoforms. The central technique used to separate proteins, 2-dimensional gel electrophoresis offers excellent separation capabilities but does not provide adequate mass accuracy. In this study, an alternative method, liquid chromatography (LC) coupled with matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF)-MS (LC-MALDI) is described. LC-MALDI-MS was used to separate and determine the mass of proteins and peptides in a complex biological sample (i.e., human pituitary gland homogenate). Peptides and proteins were first separated by capillary chromatography and the eluent mixed post-column with sinapinic acid matrix. The flow was then deposited directly onto a standard MALDI target via a capillary nebulizer. In addition to offering high mass accuracy, this method can be applied to peptide and protein quantification.

Endoplasmic reticulum stress is a determinant of retrovirus-induced spongiform neurodegeneration

FrCas(E) is a mouse retrovirus that causes a fatal noninflammatory spongiform neurodegenerative disease with pathological features strikingly similar to those induced by transmissible spongiform encephalopathy (TSE) agents. Neurovirulence is determined by the sequence of the viral envelope protein, though the specific role of this protein in disease pathogenesis is not known. In the present study, we compared host gene expression in the brain stems of mice infected with either FrCas(E) or the avirulent virus F43, differing from FrCas(E) in the sequence of the envelope gene. Four of the 12 disease-specific transcripts up-regulated during the preclinical period represent responses linked to the accumulation of unfolded proteins in the endoplasmic reticulum (ER). Among these genes was CHOP/GADD153, which is induced in response to conditions that perturb endoplasmic reticulum function. In vitro studies with NIH 3T3 cells revealed up-regulation of CHOP as well as BiP, calreticulin, and Grp58/ERp57 in cells infected with FrCas(E) but not with F43. Immunoblot analysis of infected NIH 3T3 cells demonstrated the accumulation of uncleaved envelope precursor protein in FrCas(E)- but not F43-infected cells, consistent with ER retention. These results suggest that retrovirus-induced spongiform neurodegeneration represents a protein-folding disease and thus may provide a useful tool for exploring the causal link between protein misfolding and the cytopathology that it causes.

Increased expression of MIP-1 alpha and MIP-1 beta mRNAs in the brain correlates spatially and temporally with the spongiform neurodegeneration induced by a murine oncornavirus

The chimeric murine oncornavirus FrCas(E) causes a rapidly progressive paralytic disease associated with spongiform neurodegeneration throughout the neuroaxis. Neurovirulence is determined by the sequence of the viral envelope gene and by the capacity of the virus to infect microglia. The neurocytopathic effect of this virus appears to be indirect, since the cells which degenerate are not infected. In the present study we have examined the possible role of inflammatory responses in this disease and have used as a control the virus F43. F43 is an highly neuroinvasive but avirulent virus which differs from FrCas(E) only in 3' pol and env sequences. Like FrCas(E), F43 infects large numbers of microglial cells, but it does not induce spongiform neurodegeneration. RNAase protection assays were used to detect differential expression of genes encoding a variety of cytokines, chemokines, and inflammatory cell-specific markers. Tumor necrosis factor alpha (TNF-alpha) and TNF-beta mRNAs were upregulated in advanced stages of disease but not early, even in regions with prominent spongiosis. Surprisingly there was no evidence for upregulation of the cytokines interleukin-1 alpha (IL-1 alpha), IL-1 beta, and IL-6 or of the microglial marker F4/80 at any stage of this disease. In contrast, increased levels of the beta-chemokines MIP-1 alpha and -beta were seen early in the disease and were concentrated in regions of the brain rich in spongiosis, and the magnitude of responses was similar to that observed in the brains of mice injected with the glutamatergic neurotoxin ibotenic acid. MIP-1alpha and MIP-1beta mRNAs were also upregulated in F43-inoculated mice, but the responses were three- to fivefold lower and occurred later in the course of infection than was observed in FrCas(E)-inoculated mice. These results suggest that the robust increase in expression of MIP-1 alpha and MIP-1 beta in the brain represents a correlate of neurovirulence in this disease, whereas the TNF responses are likely secondary events.

Restoration of the Epstein-Barr virus ZEBRA protein's capacity to disrupt latency by the addition of heterologous activation regions

The ZEBRA protein has a unique biological function among herpesviral proteins. It is responsible for the disruption of Epstein-Barr virus (EBV) latency and the induction of the lytic cycle. ZEBRA is a bZIP transcriptional activator which binds as a dimer to 7-bp response elements within EBV promoters and is directly involved in the stimulation of virus replication at the EBV lytic origin. We have employed the ZEBRA/EBV biological system to test whether a heterologous activation domain can substitute for another activation domain (the ZEBRA domain). The ZEBRA activation region was replaced with the potent acid activation region from the herpes simplex virus VP16 protein or with the activation region of the EBV R protein. Both chimeras were found to transactivate model and native promoters at equivalent or better levels than ZEBRA itself. Activation was not target- or cell-type dependent, nor was it dependent on the presence of virus. These activation domains restored ZEBRA's ability to induce early antigen and to stimulate origin replication to levels that were equal to or greater than those of wild type. These studies suggest that the specificities of some of the known biological functions of ZEBRA are not dependent upon the nature of the activation domain present within ZEBRA.