Hypertrophy of cultured adult rat ventricular cardiomyocytes induced by antibodies against the insulin-like growth factor (IGF)-I or the IGF-I receptor is IGF-II-dependent.

Antibodies against the insulin-like growth factor-I (IGF-I) or the IGF-I receptor (IGF-IR) directly initiate a rapid (within 6 h) hypertrophy of isolated adult rat ventricular cardiomyocytes cultured in the absence of serum. Further, cardiomyocytes treated with either of these agonistic antibodies upregulate the expression of their genes for insulin-like growth factor-II (IGF-II) and the IGF-II receptor (IGF-IIR). Genistein, an inhibitor of the tyrosine kinase IGF-IR, also induces the cardiomyocytes to hypertrophy. Anti-IGF-II antibody inhibits the cardiomyocyte hypertrophy induced by anti-IGF-I and anti-IGF-IR antibodies or by genistein. Results are consistent with a model in which local production of IGF-II is upregulated when the IGF-IR signaling pathway is blocked and in which an IGF-II-mediated pathway, likely involving the IGF-IIR, then stimulates hypertrophy of the cardiomyocytes.