Prolactin inhibits cell loss and decreases matrix metalloproteinase expression in the involuting mammary gland but fails to prevent cell loss in the mammary glands of mice expressing iGFBP-5 as a mammary transgene

Flint, D.J. and Boutinaud, M. and Whitelaw, C.B.A. and Allan, G.J. and Kolb, A.F. (2006) Prolactin inhibits cell loss and decreases matrix metalloproteinase expression in the involuting mammary gland but fails to prevent cell loss in the mammary glands of mice expressing iGFBP-5 as a mammary transgene. Journal of Molecular Endocrinology, 36. pp. 435-448. ISSN 0952-5041 (http://dx.doi.org/10.1677/jme.1.01873)

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Abstract

Insulin-like growth factor-binding protein 5 (IGFBP-5) mediates involution of the mammary gland. The decrease in DNA content and mammary gland weight which accompanies involution was inhibited by prolactin (PRL) in wild-type but not transgenic mice expressing IGFBP-5. Phospho-STAT5 protein levels were significantly lower in IGFBP-5 transgenic mice during lactation suggesting that IGFBP-5 antagonises PRL signalling in the mammary epithelium. In contrast, phospho-STAT3 levels increased during involution to a similar extent in both wild-type and transgenic mice and were unaffected by PRL. PRL inhibited gene expression of matrix metalloproteinases (MMPs) 3 and 12 but not tissue plasminogen activator or plasmin in wild-type and transgenic animals. The effects of PRL on MMPs appear to be indirect since PRL failed to inhibit MMP-3, -7 or -12 expression in HC-11 cells or in a co-transfection including an activated PRL receptor, STAT5 and a MMP-3-luciferase reporter gene. PRL is a potent inhibitor, both of cell death, an effect which is suppressed by IGFBP-5, and of MMP expression, which is independent of the actions of IGFBP-5.

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