Regulation of bovine mammary epithelial cell response by autocrine IGF-I and by collagen I [electronic resource] /
Understanding how insulin-like growth factor-I (IGF-I) signaling in mammary epithelial cells may be modified or interrupted by modifications in the cellular environment may lead to 1) methods to increase the growth and proliferation of normal mammary epithelial cells for an increase in the amount of milk produced on a per animal basis or to 2) the development of medical interventions to disrupt the growth and proliferation of cancerous mammary epithelial cells. IGF-I, a signaling protein provided by stromal cells and through the bloodstream, stimulates the proliferation of mammary epithelial cells and is crucial for mammary development. Collagen I is an extracellular matrix protein (ECM) found in skin and in other connective tissues throughout the body. The guiding question in this dissertation was how IGF-I signaling and how binding protein profile were influenced by autocrine IGF-I and by collagen I. The MAC-T cell line was chosen as the cell model utilized in these investigations because it is an immortalized bovine mammary epithelial cell line known to retain hormonal responsiveness to IGF-I. It was hypothesized that the production of IGF-I by mammary epithelial cells (autocrine secretion) would alter the response of these cells to additional IGF-I by de-sensitizing the IGF-I receptor on the cell surface. The normal mammary epithelial cell does not produce IGF-I and responds to IGF-I supplied either by stromal cells (paracrine pathway) or through the bloodstream (endocrine pathway). The IGF-I secreting bovine mammary epithelial cell line was investigated for the response of the cells to autocrine IGF-I, and the response was compared to the normal, parental cell line. To examine the effect of autocrine IGF-I on the cells, IGF-I was added both to MAC-T cells and to cells transfected to secrete IGF-I (SV40-IGF-I). The cell response of the two cell lines was compared using microphysiometry, a tool that measures IGF-IR stimulation by detecting resultant extracellular acidification. It was found that the SV40-IGF-I cell line retains IGF-I receptor sensitivity, yet, unlike the parental cell line, does not proliferate in response to IGF-I. Both cell lines exhibited increased protein synthesis in response to IGF-I as measured by amino acid uptake (AIB incorporation), but the lack of a proliferation response to additional IGF-I in the SV40-IGF-I cell line suggested that the autocrine cell line exhibited an un-coupling of IGF-IR stimulation with downstream cell proliferation. Both autocrine IGF-I and added IGF-I increased the amount of IGFBP-3 secreted by the cells into growth media.