HMG-1 as regulatory trans-acting protein in the acute phase-induced expression of the rat liver haptoglobin gene.

Expression of the haptoglobin (Hp) gene is liver specific and acute phase (AP) responsive. It was previously shown that transcriptional induction process of the rat Hp gene during turpentine induced AP response has been mediated by the liver nucleoprotein p29 which was shown to be homologous to the HMG-1 chromatin-associated protein. The results presented in this report offered further evidence for the existence of structural and functional similarities between these two proteins implicating an involvement of HMG-1 in the regulation of the rat Hp gene transcription. By DNA binding assays we found the HMG-1 binding sites in the rat Hp gene cis-regulatory subelements A and C and revealed an increase in its DNA-binding after induction of AP response. In view of our previous and here shown data we assume that this increase could be a consequence of AP-induced release of HMG-1 from the chromatin and subsequent increase in its nuclear amount.