Regulation of C/EBPβ/NF-M Activity by Kinase Oncogenes

The Role of p38 Mitogen-Activated Protein Kinase in IL-1β Transcription

Several reports have shown that bicyclic imidazoles, specific inhibitors of the p38 mitogen-activated protein kinase (MAPK), block cytokine synthesis at the translational level. In this study, we examined the role of p38 MAPK in the regulation of the IL-1β cytokine gene in monocytic cell lines using the bicyclic imidazole SB203580. Addition of SB203580 30 min before stimulation of monocytes with LPS inhibited IL-1β protein and steady state message in a dose-dependent manner in both RAW264.7 and J774 cell lines. The loss of IL-1β message was due mainly to inhibition of transcription, since nuclear run-off analysis showed an ∼80% decrease in specific IL-1 RNA synthesis. In contrast, SB203580 had no effect on the synthesis of TNF-α message. LPS-stimulated p38 MAPK activity in the RAW264.7 cells was blocked by SB203580, as measured by the inhibition of MAPKAP2 kinase activity, a downstream target of the p38 MAPK. CCAATT/enhancer binding protein (C/EBP)/NFIL-6-driven chloramphenicol acetyltransferase (CAT) reporter activity was sensitive to SB203580, indicating that C/EBP/NFIL-6 transcription factor(s) are also targets of p38 MAPK. In contrast, transfected CAT constructs containing NF-κB elements were only partially inhibited (∼35%) at the highest concentration of SB203580 after LPS stimulation. As measured by EMSA, LPS-stimulated NF-κB activation was not affected by SB203580. Overall, the results demonstrate, for the first time, a role for p38 MAPK in IL-1β transcription by acting through C/EBP/NFIL-6 transcription factors.

Regulation of LPS-mediated induction of C/EBP delta gene expression in livers of young and aged mice

The C/EBP family of transcription factors plays a major role in the regulation of families of stress response genes, in particular, the acute phase response genes. We have examined expression of the C/EBP delta gene during the bacterial lipopolysaccharide mediated induction of the acute phase response in livers of young (4 months) and aged (24-28 months) male C57B1/6 mice by Northern, Western, and Southwestern analyses. C/EBP delta mRNA is present at a low constitutive level, is induced by lipopolysaccharide, and reaches the same induced level in young and aged mice. Aged mice, however, show a higher constitutive, uninduced mRNA pool level and a delay in recovery to uninduced levels after lipopolysaccharide treatment. C/EBP delta mRNA is observable 30 min after lipopolysaccharide in total RNA, cytoplasmic and polysomal fractions. Specific full length 28-kDa nascent peptides are detectable in polysomes 90 min after lipopolysaccharide. mRNA and nascent peptides cosediment with large polysomes and C/EBP delta mRNA is shifted to larger polysomes in lipopolysaccharide treated aged mice, consistent with an increased rate of initiation. Specific DNA-binding activity of C/EBP delta protein in nuclear extracts was examined by electromobility shift and antibody supershift assay. The levels of C/EBP delta binding-activity, are consistent with the changes in mRNA levels in young lipopolysaccharide treated livers. These studies support our hypothesis that aged mice exhibit a state of chronic inflammation or stress in the absence of a stressor.

Lactation status influences expression of CCAAT/enhancer binding protein isoform mRNA in the mouse mammary gland

The CCAAT/enhancer binding proteins (C/EBPs) are a highly conserved family of DNA binding proteins implicated in the transcriptional control of genes involved in cell growth and differentiation in a variety of tissues. The expression of C/EBP-alpha, beta, and delta mRNA in the normal mouse mammary gland was investigated during pregnancy, lactation, and involution via Northern blotting and in situ hybridization. Mammary gland C/EBP-alpha mRNA is detectable at low levels during pregnancy and postlactational involution. C/EBP-beta mRNA levels are elevated during pregnancy, decline slightly in midlactation, and are induced within 48 hours of the onset of involution. C/EBP-delta mRNA content is low throughout pregnancy and lactation, but increases dramatically (>100-fold) within 12 hours after the onset of postlactational involution. In situ hybridization demonstrates that mammary epithelial cells are responsible for the expression of C/EBP-delta mRNA during involution. In contrast to mammary gland, C/EBP-alpha is the predominate isoform expressed in liver with relatively low expression of C/EBP-beta and C/EBP-delta mRNA. Liver C/EBP isoform mRNA levels are unaffected by lactation status. These results demonstrate the tissue-specific regulation of C/EBPs. The pronounced sequential induction of C/EBP-delta and C/EBP-beta during postlactational involution is consistent with a role for C/EBPs in the regulation of mammary epithelial cell apoptosis.