Effects of mercuric chloride on the regulation of expression of the acute phase response components alpha(1)-acid glycoprotein and C/EBP transcription factors

alpha1-Acid glycoprotein production in rat dorsal air pouch in response to inflammatory stimuli, dexamethasone and honey bee venom

This study shows the rapid and differential production of the 40-43 kDa and the 70-90 kDa alpha1-acid glycoprotein (AGP) fucosylated glycoforms after treatment of the dorsal air pouch with bacterial lipopolysaccharide (LPS), HgCl(2) or Freund's complete adjuvant (FCA). The 40-43 kDa and the 70-90 kDa AGP production is peaked 1-3 h post-LPS treatment. We observed that the responses to LPS and FCA are similar in that both AGP isoforms are induced whereas they differ in that the FCA exhibits a 6 h lag period. The response to HgCl(2,) however, exhibits the specific biphasic induction only of the 40-43 kDa AGP. The serum 40-43 kDa AGP glycoform gradually increases in response to all of the above stimulants and peaks by 24 h post- treatment. The increase of the 70-90 kDa AGP levels in the air pouch occurs in association with the accumulation of polymorphonuclear (PMN) cells while dexamethasone (DEX) increases only the 40-43 kDa AGP production in the absence of PMN accumulation. Macrophage-monocyte lineage cells forming the air pouch lining tissue may potentially be the cells that secrete the 40-43 kDa AGP while polymorphonuclear cells that infiltrate the air pouch secrete the 70-90 kDa AGP. The 40-43 kDa and 70-90 kDa AGP production induced by LPS in the air pouch precedes that of interleukin-1 (IL-1) or interleukin-6 (IL-6) while the 40-43 kDa AGP glycoform potentially increases IL-6 production by air pouch PMN exudate cells. These significant differences suggest a local pro-inflammatory role of AGP. Honeybee venom suppressed arthritis development and exhibited differential local or systemic regulation of AGP in serum vs. air pouch exudate or synovial fluid. This study with the air pouch model of facsimile synovium tissue suggests that local alpha1-acid glycoprotein (AGP) production may contribute to pro-inflammatory and anti-inflammatory activities during the local acute phase response or during chronic inflammatory stress as in arthritis.

Age-dependent response of CCAAT/enhancer binding proteins following traumatic brain injury in mice

Exacerbated inflammatory responses have been reported following traumatic injury to the aged brain. The present study was designed to investigate the involvement of the transcription factors belonging to the CCAAT/enhancer binding protein (C/EBP) family that regulate expression of many of the pro-inflammatory genes which show increased expression following injury to the aged brain. Controlled cortical impact injury was induced in adult (5-6 months) and aged (22-24 months) C57/BL6 mice. C/EBP mRNA and protein expression were analyzed in injured cortex at 1, 3, and 7 days post-injury. Expression of C/EBPalpha was reduced relative to baseline at day 1 in both adult and aged mice, whereas, it increased at days 3 and 7 post-injury. No significant differences were observed between adult and aged brain. Upregulation of C/EBPbeta was observed 1 day following injury in both the adult and aged brain, but there were no major age-related differences in mRNA levels. However, there was higher C/EBPbeta protein in the aged brain. C/EBPdelta expression increased beginning 1 day post-injury in both adult and aged brain. In this case, the increase in C/EBPdelta expression was higher in the aged brain than in the adult at all time points studied. Expression of CCAAT/enhancer binding protein homologous protein (CHOP), a transcription factor involved in ER stress and protein unfolding responses, was also up-regulated in response to injury, but CHOP levels were significantly lower in the aged than the adult brain. Based on these results, we conclude that differential expression of C/EBP beta, delta and CHOP might contribute to the hyper-inflammatory response and poor prognosis following traumatic brain injury in the elderly patients. In addition elevated C/EBPdelta levels following TBI in the aged brain may play a role in the link between TBI and Alzheimer's disease.

Regulation of CCAAT/enhancer-binding protein-beta isoform synthesis by alternative translational initiation at multiple AUG start sites

The mRNA of the intronless, single-copy CCAAT/enhancer-binding protein-beta (C/EBPbeta) gene encodes several isoforms that have truncated transcription activation domains. This occurs by the alternative translational initiation (ATI) at multiple AUG start sites. The C/EBPbeta mRNA has four in-frame AUGs and an internal out-of-frame AUG associated with a small open reading frame (sORF). Initiation of translation at the in-frame AUGs forms 40-kDa (AUG-1), 35-kDa (AUG-2), 20-kDa (AUG-3) and 8.5-kDa (AUG-4) isoforms. We show that in COS-1 cells the 20-kDa isoform is not a product of proteolysis of the higher molecular weight isoforms. The sORF contains an AUG and termination signal that may produce the oligopeptide MPPAAARRL. Our studies suggest that ATI involves three mRNA structural features: (i) the cap structure, (ii) the context of the Kozak sequences that flank the AUG and (iii) the integrity of the sORF. We propose that formation of C/EBPbeta isoforms is accomplished by a leaky ribosomal scanning mechanism that facilitates ATI of multiple internal AUGs.