Lj. Sevaljevic et al., ACUTE PHASE-DEPENDENT CHANGES IN THE BINDING OF RAT-LIVER NUCLEOPROTEINS TO THE CYTOKINE RESPONSE ELEMENT OF THE RAT HAPTOGLOBIN GENE, International journal of biochemistry & cell biology, 27(2), 1995, pp. 185-194
Hormones released during the acute phase reaction promote the transcri
ptional activation of the haptoglobin (Hp) gene and a consequent incre
ase of Hp protein synthesis in the liver. The mechanisms underlying th
e alterations of basal transcription rates of eukaryotic genes are ass
umed to result from modulations of the binding affinities between nucl
eoproteins and specific DNA sequences in the enhancer and promoter ele
ments. In order to characterize the changes in the interaction of nucl
eoproteins with the promoter that accompany the induction of the Hp ge
ne, nuclear extracts from normal and inflamed livers were probed with
hormone responsive element (HRE) of the rat Hp gene by gel mobility sh
ift and Southwestern assays. Each of the three cis-acting sequences of
the HRE, elements A, B, and C, recognized a distinct set of proteins.
Together they conferred an additional level of specificity to the pro
tein binding sites of the entire ABC-element. These sites were recogni
zed by proteins in liver nuclear extracts isolated from both control a
nd treated rats. The differences in the gel shift and Southwestern pat
terns of the corresponding DNA-protein complexes suggested that transc
riptional activation of the Hp gene relied on changes in the concentra
tions and/or functional modifications of preexisting proteins rather t
han on the induction of new trans-acting factors.