Real-time detection of insulin-like growth factor-1 stimulation of the MAC-T bovine mammary epithelial cell line

Binding of growth factors by cell-surface receptors is an essential means b y which cells regulate normal tissue growth and differentiation. Exposure t o growth factors is often transient, and our goal was to determine whether short-term exposure to insulin-like growth factor-1 (IGF-1) would lead to a ctivation, assayed as cell proliferation, of mammary epithelial cells. The MAC-T cell line is an immortalized bovine mammary epithelial cell line, cho sen as our model mammary cell line because of its known sensitivity to IGF- 1. Using the Cytosensor(R) Microphysiometer System, a biosensor capable of measuring extracellular acidification, we were able to measure activation o f the cells owing to IGF-1 addition in real time and found that peak acidif ication occurred in only 14 min. We show that this rapid response to IGF-1 is dose dependent and specific for IGF-1. A significant increase in [H-3]th ymidine incorporation by cells after a similar short-term exposure to IGF-1 suggests that the measured increase in extracellular acidification followi ng IGF-1 addition is physiologically relevant. This technology offers a new , novel, and rapid means for the study of IGF-1 activity, as well as the sc reening of IGF-1 inhibitors, in mammary epithelial cells.