Autocrine regulation of growth in cultured human intestinal muscle by growth factors

Background & Aims: Transforming growth factor (TGF)-alpha, insulin-like growth factor (IGF)-I, and TGF-beta 1 are expressed in vivo by intestinal smooth muscle. The aim of this study was to determine whether these growth factors were produced by human intestinal muscle cells in culture and to identify their roles in regulating growth. Methods: Muscle cells were examined at various times in culture: during vapid growth (day 3), at confluence (day 7), and after confluence (day 14). Growth factor production was measured by radioimmunoassay or enzyme-linked immunosorbent assay. Growth was measured from [H-3]thymidine incorporation. Results: Production of pro-TGF-alpha and TGF-alpha (1550 +/- 100 and 1260 +/- 150 pg/mg protein, respectively) and free IGF-I (86.2 +/- 23.7 ng/mg protein) was highest during rapid growth and 3-40-fold lower later in culture. Production of soluble and latent TGF-beta 1 was highest in postconfluent cells (280 +/- 74 and 4320 +/- 610 pg/mg protein, respectively) and 4-7 fold lower earlier in culture. TGF-alpha and IGF-I caused concentration-dependent stimulation of growth in rapidly growing cells. TGF-beta 1 caused concentration-dependent inhibition of growth predominantly in postconfluent cells. Neutralizing antibodies to TGF-alpha or IGF-I inhibited growth and neutralizing antibody to TGF-beta augmented growth. Conclusions: Human intestinal muscle cells produce TGF-alpha, IGF-I, and TGF-beta 1 in a time-dependent reciprocal fashion that parallels their effects on growth.