EXPRESSION OF EPIDERMAL GROWTH FACTOR-RELATED PROTEINS IN THE AGED ADULT-MOUSE MAMMARY-GLAND AND THEIR RELATIONSHIP TO TUMORIGENESIS

Mammary glands from female BALB/c mice of different ages and parity we re screened for production of three epidermal growth factor (EGF) rela ted transforming growth factors and their corresponding mRNAs. Glands were obtained from 2-26-month-old nulliparous, 4-26-month-old parous, and 2-8-month-old midpregnant mice. Reverse-transcribed polymerase cha in reaction (RT-PCR) was used to screen for mRNA from the transforming growth factor alpha (TGF alpha), cripto-1 (CR-1), and amphiregulin (A R) genes in extracts of whole mammary glands. TGF alpha, CR-1, and AR transcripts were detected in all of the mammary glands assayed. in sit u hybridization was then used to localize these mRNAs among various ce ll types in sections of glands. TGF alpha mRNA levels were low in the mammary epithelium from young nulliparous mice, high in the stroma of midpregnant mammary glands, and highest in luminal epithelium of the a ged glands. AR mRNA levels were high and remained unchanged in all dev elopmental stages. CR-1 mRNA level increased with age and was detected primarily in epithelium, with some scattered expression in adjacent s troma. Finally, TGF alpha CR-1, and AR proteins were immunolocalized i n histological sections of mammary glands from the various development al stages. TGF alpha was detected sporadically in midpregnant mice, wi th more conspicuous reactivity seen in 18-26-month-old mice (38% of mi ce). CR-1 immunoreactivity was detected in 100% of the 18-26-month-old glands but not in any other age groups. Strong AR immunoreactivity wa s observed in in all glands, including 100% of the 18-26-month-old gla nds. Staining for all three of these growth factors was observed prima rily in the epithelium, with some reactivity detected in the periducta l fibroblasts. No significant difference was discerned between glands from nulliparous and parous animals. We also found intense CR-1 and AR mRNA expression and strong immunoreactivity in seven different carcin ogen-induced and eight spontaneous mammary tumors. Our results demonst rate that these growth factors accumulate in significant amounts in th e old gland of both nulliparous and parous mice. The observations sugg est that these growth factors are positioned to contribute to abnormal development in the older mammary gland, predisposing them to tumorige nesis. (C) 1997 Wiley-Liss, Inc.