PHOSPHORYLATION OF THE PRECURSOR SEQUENCE OF RAT B-TYPE NATRIURETIC PEPTIDE BY P34(CDC2) AND MAP KINASE

Atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP), two distinct members of the natriuretic peptide family, share many fe atures in common. However, differences in expression indicate that the processing mechanisms must be different. The leader sequence of rat B NP contains three potential phosphorylation sites for proline-directed kinases that are not present in the leader sequence of ANP. This stud y has examined how these sites are used by two somewhat different prol ine-directed kinases. A peptide containing these sites was phosphoryla ted in vitro by HeLa p34(cdc2) kinase and by sea star p44(mpk) kinase at rates that were comparable to the rates with peptide substrates tha t are used to assay these enzymes. Sequence analysis of the phosphopep tide shows that both kinases phosphorylate only the two potential phos phorylation sites surrounding the cleavage site of the BNP precursor. The enzymatic potential for such a phosphorylation of BNP in cardiac t issue is demonstrated by immunoblots and kinase assays, showing that i n fetal and in adult rat heart both the atria and the ventricles conta in a mitogen-activated protein kinase homologue that can phosphorylate this preproBNP sequence.