When hypertrophic growth is induced in neonatal rat cardiocytes by stretching, the cardiocytes express high levels of brain-type
natriuretic peptide (BNP) and the proprotein-processing
enzyme furin. A BNP precursor, gammaBNP, possesses a
furin-cleavable Arg-X-X-Arg motif, which is cleaved when gammaBNP is processed to form
BNP-45. The Arg-X-X-Arg motif is found in many precursors of
growth factors and growth-related
proteins. To determine if
furin converts gammaBNP to
BNP-45 as well as other unidentified growth-promoting
protein precursors to their active form that may induce hypertrophic growth in cardiocytes, we used two
protease inhibitor systems, synthetic peptidyl chloromethyl
ketones (CMK) (dec-
Arg-Val-Lys-Arg-CMK and dec-
Phe-Ala-Lys-Arg-CMK; where dec is decanoyl) and
vaccinia vector-integrated native and variant alpha1-antitrypsins. The
furin-specific inhibitors, dec-
Arg-Val-Lys-Arg-CMK and variant alpha1-antitrypsin with the inhibitory determinant Arg-X-X-Arg, suppressed the stretch-induced hypertrophic growth of cardiocytes as well as the processing of gammaBNP to
BNP-45. The other
serine protease inhibitors and variant alpha1-antitrypsin against
elastase, or
thrombin, however, neither suppressed the hypertrophic growth nor prevented the processing of gammaBNP to
BNP-45. Thus, we suggest that
furin catalyzes the conversion of gammaBNP to
BNP-45 as well as growth-promoting proproteins to their active form, which might induce hypertrophic growth in cardiocytes.