COORDINATE REGULATION BY DIETHYLSTILBESTROL OF THE PLATELET-DERIVED GROWTH FACTOR-A (PDGF-A) AND FACTOR-B CHAINS AND THE PDGF RECEPTOR ALPHA-SUBUNIT AND BETA-SUBUNIT IN THE MOUSE UTERUS AND VAGINA - POTENTIAL MEDIATORS OF ESTROGEN ACTION

The effects of estrogen on the reproductive tract involve cell proliferation, migration, and differentiation, which need to be well coordinated. Polypeptide growth factors are believed to play a vital role in a number of these cellular processes. Among the growth factors now documented to be associated with estrogen action are epidermal growth factor, transforming growth factor-alpha (TGF alpha), transforming growth factor-beta 1 (TGF beta 1), TGF beta 2, TGF beta 3, and insulin-like growth factor-I (IGF-I). Platelet-derived growth factors (PDGFs) are also potent mitogens, which consist of two peptide chains, denoted A and B, that dimerize to isoforms (PDGF-AA, -AB, and -BB) which differ in their functional properties, secretory behavior, receptor binding, and physiological effects. To study the role of the PDGF-A and -B chains and the PDGF receptor subunits, alpha and beta, during estrogen action in the mouse reproductive tract, time-dependent changes in the expression of these genes were examined by Northern and in situ RNA. analyses and by immunohistochemistry after a single treatment of immature CD-1 (17- to 19-day-old) mice with the synthetic estrogen, diethylstilbestrol (DES). Our results demonstrate estrogen modulation of the expression of messenger RNA (mRNA) and protein for the PDGF ligands and receptors in both the uterus and vagina of the mouse. Northern and in situ RNA analyses demonstrate time-dependent estrogen induction of the mRNA levels for these genes in both tissues within 3 h after treatment. However, distinctive mRNA expression profiles for the PDGF ligand and receptor genes are exhibited by the uterus and vagina in response to DES, especially in that the induction of transcripts for PDGF-A and both receptor subunits is more transient in the vagina than in the uterus. Steroid specificity studies demonstrate predominant estrogen-specific regulation of mRNA induction for these genes. Analysis of cell-specific RNA expression by in situ hybridization reveals prominent induction of transcripts for the PDGF chains and receptor subunits in the uterine and vaginal epithelium after estrogen treatment, although enhanced expression of mRNA is also noted in the stroma, particularly for the PDGF receptor subunit genes. Cellular localization of the PDGF ligand and receptor protein molecules by immunohistochemistry detected significant immunostaining for all of these proteins in both the uterus and vagina of control animals. After DES treatment, the uterus exhibits a significant decrease in the level of PDGF ligand and receptor proteins immunostained within 6 h, whereas less dramatic effects are observed in the vagina. Affinity labeling of PDGF alpha-receptor with [I-125]PDGF-AA establishes the presence of functional PDGF ct-receptor in the uterus and vagina. Estrogen treatment is found to reduce the amount of PDGF alpha-receptor that can be covalently labeled in both tissues, especially in the uterus. This reduction in affinity labeling of the PDGF receptor is in agreement with the finding of decreased immunostaining for the PDGF receptors in these tissues and supports estrogen modulation of PDGF receptors in the reproductive tract. The induction of the PDGF ligand and receptor genes by estrogen is a relatively early event, occurring many hours before the initiation of DNA synthesis in the uterine and vaginal epithelium, which implicates the PDGF signal transduction pathway in estrogen-mediated growth. Based on the coexpression of the potent PDGF mitogens and their receptors in the mouse reproductive tract, our findings demonstrate the presence in vivo of another powerful autocrine or paracrine loop that is regulated by estrogen, which probably plays an important role in estrogen action by coordinating growth and differentiation. Collectively, these data and other in vivo studies have now shown that estrogen regulates multiple peptide growth factors in the reproductive tract, which suggest that estrogen stimulation of DNA synthesis may be controlled by potent competence (PDGF and PDGF receptors) and progression (TGF alpha, epidermal growth factor, IGF-I, IGF-II, and their receptors) factors interacting by autocrine/paracrine mechanisms to insure a synchronized integrated tissue growth response.