Synthesis of extracellular matrix and adhesion through beta(1) integrins are critical for fetal ventricular myocyte proliferation

Extracellular matrix (ECM) regulates vascular smooth muscle cell proliferat ion. The role of ECM in myocardial growth is unexplored. We sought to deter mine whether human fetal ventricular myocytes (HFVMs) produce ECM and wheth er synthesis and attachment to ECM are necessary for their epidermal growth factor (EGF)-dependent and -independent proliferation. Cultured HFVMs prol iferate in the presence but not absence of serum and EGF, as determined by increase in cell number and [H-3]thymidine and [C-14]leucine incorporation (measures of DNA and protein synthesis, respectively). Using a cyanogen bro mide digestion technique to measure collagen and elastin and using affinity chromatography for fibronectin, we found that HFVMs synthesized collagen a nd fibronectin but not elastin. HFVMs grown on exogenous ECM (including fib ronectin and type I collagen and laminin) demonstrated no change in prolife ration or DNA and protein synthesis with or without EGF. However, inhibitio n of collagen synthesis using cis-4-hydroxyproline resulted in a decrease i n EGF-related HFVM proliferation and DNA and protein synthesis, which was:r eversed by exposure to L-proline but not by growth on type I collagen, Use of beta(1) but not beta(3) integrin antibody to inhibit cell interaction wi th ECM resulted in a decrease in HFVM proliferation and DNA and protein syn thesis in response to EGF. Furthermore, EGF-dependent proliferation was enh anced by alpha(1)beta(1) and alpha(5)beta(1) antibodies that act as functio nal ligands, but not alpha(3)beta(1), the only beta(1) subtype expressed in adult myocytes. In conclusion, proliferating HFVMs synthesize collagen and fibronectin. The proliferative response of HFVMs to EGF requires the synth esis of collagen as well as attachment to specific alpha/beta(1) integrin h eterodimers.