Lactogenic hormones and extracellular matrix regulate expression of IGF-1 linked to MMTV-LTR in mammary epithelial cells.
The cell line MD-IGF-1, containing an ovine IGF-1 cDNA driven by the mouse mammary tumor virus-long terminal repeat (MMTV-LTR) promoter, was used to study expression of IGF-1 linked to the MMTV-LTR in bovine mammary epithelial cells in response to various hormonal and substratum stimuli. Acute sensitivity of the MMTV-LTR promoter to glucocorticoids and sex steroids was ascertained by transient transfection of parental MAC-T cells with an MMTV-CAT construct. Specifically, CAT activity was induced by glucocorticoids, but not by 17 beta-estradiol or progesterone. Induction of MD-IGF-1 cells with dexamethasone (DEX) alone triggered a 29.5-fold increase in secretion of recombinant IGF-1 (348.9 vs 11.8 pg/micrograms DNA), and stimulated a 1.7-fold increase in total DNA within 72 h. Growth of MD-IGF-1 cells was enhanced by exogenous IGF-1, insulin, and TGF-alpha. In contrast, TGF-beta inhibited cell proliferation, while epidermal growth factor, estrogen, progesterone, and testosterone had no effect. Extracellular matrix from the Engelbreth-Holm-Swarm (EHS) tumor, in the presence of DEX, prolactin (PRL), and insulin stimulated a 29.4-fold increase in secretion of IGF-1 (591.9 pg/microgram DNA), compared with cells in absence of hormones (20.1 pg/micrograms DNA). EHS and DEX plus PRL triggered a 63.2-fold increase in IGF-1 secretion (689.1 pg/micrograms DNA), compared with MD-IGF-1 cells cultured on plastic (10.9 pg/micrograms DNA), in the absence of hormones. These data indicate that the MMTV-LTR is regulated by both lactogenic hormones and extracellular matrix in MD-IGF-1 cells and that the MMTV-LTR may be a useful regulatory element for targeting expression of foreign proteins in bovine mammary epithelial cells.
Romagnolo
D
D
Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061-0315.
Akers
R M
RM
Wong
E A
EA
Boyle
P L
PL
McFadden
T B
TB
Byatt
J C
JC
Turner
J D
JD
D000818:Animals; D001940:Breast / Q000166:cytology / Q000378:metabolism*; D002417:Cattle; D002460:Cell Line; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D005109:Extracellular Matrix / Q000502:physiology*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D006133:Growth Substances / Q000502:physiology; D006728:Hormones / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000235:genetics; D008324:Mammary Tumor Virus, Mouse / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D012756:Sheep
D006133:Growth Substances; D006728:Hormones; D007334:Insulin-Like Growth Factor I