Phosphorylation of the precursor sequence of rat B-type natriuretic peptide by p34cdc2 and MAP kinase

Atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP), two distinct members of the natriuretic peptide family, share many features in common. However, differences in expression indicate that the processing mechanisms must be different. The leader sequence of rat BNP contains three potential phosphorylation sites for proline-directed kinases that are not present in the leader sequence of ANP. This study has examined how these sites are used by two somewhat different proline-directed kinases. A peptide containing these sites was phosphorylated in vitro by HeLa p34cdc2 kinase and by sea star p44mpk kinase at rates that were comparable to the rates with peptide substrates that are used to assay these enzymes. Sequence analysis of the phosphopeptide shows that both kinases phosphorylate only the two potential phosphorylation sites surrounding the cleavage site of the BNP precursor. The enzymatic potential for such a phosphorylation of BNP in cardiac tissue is demonstrated by immunoblots and kinase assays, showing that in fetal and in adult rat heart both the atria and the ventricles contain a mitogen-activated protein kinase homologue that can phosphorylate this preproBNP sequence.