Cloning and regulation of the rat activin β(E) subunit

Using a combination of polymerase chain reaction (PCR) procedures, we have cloned and sequenced the rat activin β(E) subunit cDNA. The putative protein corresponding to the prepro-activin β(E) subunit was predicted to comprise 350 amino acids which, when cleaved between amino acid residues 236 and 237, would yield a mature polypeptide of approximately M(r) 12 500 with a predicted pI of 5-1. Two cDNA transcripts for activin β(E) were identified; these differed by 738 bp in the 3'-untranslated region. Activin β(E) mRNA transcripts were expressed only in rat liver and lung tissue as assessed by Northern blotting and PCR analysis. Relatively higher levels of both transcripts were found in the liver, whereas the lung contained lower levels that were detectable by PCR only. In situ hybridization data showed that, within the liver, activin β(E) mRNA was localized to hepatocytes. In vivo treatment with lipopolysaccharide as a means of activating the immune system and the hepatic acute-phase response resulted in stimulated activin β(E) mRNA levels, compared with untreated, control rats. This increased expression was accompanied by a preferential increase in the amount of the long activin β(E) transcript over the shorter transcript. These findings suggested that the two activin β(E) mRNA transcripts may be products of alternative splicing events or use alternative polyadenylation sites which are differentially regulated during inflammation. These data provide evidence of a role for activin β(E) in liver function and inflammation in the rat.