STAT3/NFκB interplay in the regulation of α2-macroglobulin gene expression during rat liver development and the acute phase response

The synthesis of alpha-2-macroglobulin (alpha M-2) is low in adult rat liver and elevated in fetal liver. During the acute-phase (AP) response it becomes significantly increased in both adult and fetal liver. In this work, the cross talk of STAT3 and NF-kappa B transcription factors during alpha M-2 gene expression was analysed. Using immunoblotting, their cellular compartmentalization was examined by comparing the cytoplasmic levels of STAT3 and NF-kappa B with their active equivalents, the 86 and 91 kDa isoforms and p65-subunit, respectively, in the nuclear extract and nuclear matrix. Different partitioning dynamics of the transcription factors were observed. At the level of protein-DNA interactions, studied by alpha M-2 promoter affinity chromatography, it was established that different ratios of promoter-binding STAT3 isoforms participated in elevated hepatic transcription in the basal state fetus and the AP-adult, but only the 91 kDa isoform in the AP-fetus. Unchanged levels of DNA-bound p65 in the control and AP-fetus suggest that it participated in constitutive transcription. The promoter-binding of p65 observed in the AP-adult suggests that it was involved in transcriptional stimulation of alpha M-2 expression. The selective enrichment of the AP-adult nuclear matrix with promoter-binding STAT3 disclosed the importance of this association in the induction of transcription. Protein-protein interactions were examined by co-immunoprecipitation. Interactions between the 86 kDa STAT3 isoform and p65 that were observed in the control and AP-fetus and of both the 86 and 91 kDa STAT3 isoforms with p65 in the AP-adult, suggest that protein-protein interactions were functionally connected to increased transcription. We concluded that alpha M-2 gene expression is driven by developmental- and AP-related mechanisms that rely on STAT3/NF-kappa B interplay.