Insulin-like growth factor binding protein (IGFBP)-5 Is upregulated during both differentiation and apoptosis in primary cultures of mouse mammary epithelial cells

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Lochrie, J.D. and Phillips, K. and Tonner, E. and Flint, D.J. and Allan, G.J. and Price, N. and Beattie, J. (2006) Insulin-like growth factor binding protein (IGFBP)-5 Is upregulated during both differentiation and apoptosis in primary cultures of mouse mammary epithelial cells. Journal of Cellular Physiology, 207. pp. 471-479. ISSN 0021-9541 (http://dx.doi.org/10.1002/jcp.20587)

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Abstract

We have previously demonstrated that insulin-like growth factor binding protein-5 (IGFBP-5) is upregulated following treatment of the mouse mammary epithelial cell line HC11 with lactogenic hormones (dexamethasone, insulin, and prolactin—DIP). In addition, we have also shown that IGFBP-5 is upregulated in mammary epithelial cells in vivo during involution of the rodent mammary gland. We have, therefore, postulated that there may be a dual regulation of IGFBP-5 expression during the temporally separated processes of differentiation and apoptosis of mammary epithelial cells. To test this hypothesis further, we have used a phenotypically differentiated model, which comprises primary cultures of mouse mammary epithelial cells grown on a layer of EHS (Engelbreth–Holm–Swarm) extracellular matrix. We show that lactogenic hormone treatment hydrocortisone, insulin, and prolactin—HIP) of these cultures induces the upregulation of IGFBP-5 thus replicating the results obtained with the HC11 cell line. In addition, following the induction of apoptosis in primary cultures fmammary epithelial cells by treatment with TGFb-3, IGFBP-5 expression is also upregulated. In parallel with this upregulation of IGFBP-5, there is also an increase in the levels of cleaved caspase-3, a well-characterized marker of cellular apoptosis. These findings confirm previous in vivo work demonstrating an increase in IGFBP-5 expression during involution of the mouse mammary gland. When HC11 cells are cultured under serum-free conditions (a well-characterized apoptotic insult in cell culture), there is also an increase in cleaved caspase-3 levels. Unexpectedly, in the presence of TGFb-3, caspase-3 levels are attenuated. In the presence of DIP, caspase-3 levels are also decreased in HC11 cells. As described previously, TGFb-3 inhibits b-casein synthesis in HC11 cells. In the HC11 cell line (in contrast to primary cultures of mammary epithelial cells), there is no evidence for TGFb-3 induction of IGFBP-5 under either serumfree or DIP-supplemented conditions.Webelieve our data with primary cultures of mammary epithelial cells support the hypothesis of dual regulation of IGFBP-5 expression during both differentiation and apoptosis in the mammary gland and emphasizes the importance of using appropriate cell culture models to investigate such phenomena in this tissue. We discuss the possible implications of our observations in relation to the physiological processes of pregnancy, lactation, and involution in the mammary gland and the associated changes in mammary epithelial cell function.

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