Estrogen regulates vascular endothelial growth/permeability factor expression in 7,12-dimethylbenz(a)anthracene-induced rat mammary tumors

Endocrinology. 1996 Dec;137(12):5589-96. doi: 10.1210/endo.137.12.8940388.

Abstract

Vascular endothelial growth/permeability factor (VEG/PF) is expressed in some normal tissues and at high levels in a wide range of tumors. This growth factor is believed to be a key mediator of angiogenesis. Recent reports have shown that VEG/PF mRNA in the normal rat uterus is stimulated by estradiol (E2). In this study, we investigated the expression of VEG/PF in the mammary gland and 7,12-dimethylbenz(a)anthracene (DMBA)-induced, hormone-dependent mammary tumor of the rat model, and also whether VEG/PF is regulated by E2. VEG/PF mRNA from tumor extracts was amplified by RT-PCR with VEG/PF primers and generated two main products which corresponded in size to those expected for VEG/PF 164 and 120. In some cases, a third product corresponding in size to that expected for VEG/PF 188 was also generated. No such PCR products were generated from equal amount of RNA from normal mammary tissue, rat brain, or liver. Using immunocytochemistry, VEG/PF expression was detected in the epithelial cells of the tumors. We developed an ELISA assay to measure VEG/PF protein concentrations and found a 4-fold difference between normal mammary glands (1.3 +/- 0.11 ng/mg protein) and tumors (4.44 +/- 0.66) (P < 0.01). E2 treatment (5 microg/rat, s.c.) of rats 24 h after ovariectomy, greatly enhanced the expression of RT-PCR products in tumors within 2 h, which reached a maximum at 6-8 h but declined by 48 h. VEG/PF concentrations were also increased 8-12 h after E2 injection. When rats were given two injections of aromatase inhibitor 4-hydroxyandrostenedione (4-OHA 10 mg/rat s.c.) 24 h apart, to reduce estrogen concentrations, a low level of RT-PCR products was maintained for at least 96 h. After a single injection of 4-OHA, RT-PCR products remained low until 36 h when an increase occurred corresponding with a rise in plasma E2 levels. Injection of E2 2 h after 4-OHA treatment, caused a rise in RT-PCR products in 6-8 h. However, there was no significant change in VEG/PF concentrations. An increase in VEG/PF protein concentrations followed the increase in mRNA levels by 4-6 h. Thus, it appears that E2 causes a rapid induction of VEG/PF expression in mammary tumors that is similar to that observed in the normal uterus. These findings suggest that one mechanism by which estrogen acts as a mammary tumor promotor is by stimulating VEG/PF, leading to increased tumor angiogenesis and/or permeability of the microvessels to allow tumor cell migration.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 9,10-Dimethyl-1,2-benzanthracene
  • Androstenedione / analogs & derivatives
  • Androstenedione / pharmacology
  • Animals
  • Endothelial Growth Factors / genetics
  • Endothelial Growth Factors / metabolism*
  • Enzyme Inhibitors / pharmacology
  • Estradiol / pharmacology*
  • Female
  • Immunohistochemistry
  • Lymphokines / genetics
  • Lymphokines / metabolism*
  • Mammary Glands, Animal / metabolism
  • Mammary Neoplasms, Animal / chemically induced
  • Mammary Neoplasms, Animal / metabolism*
  • Ovariectomy
  • RNA, Messenger / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Reference Values
  • Time Factors
  • Vascular Endothelial Growth Factor A
  • Vascular Endothelial Growth Factors

Substances

  • Endothelial Growth Factors
  • Enzyme Inhibitors
  • Lymphokines
  • RNA, Messenger
  • Vascular Endothelial Growth Factor A
  • Vascular Endothelial Growth Factors
  • Androstenedione
  • Estradiol
  • 9,10-Dimethyl-1,2-benzanthracene
  • formestane