VEGF, a potent angiogenic
growth factor, is up-regulated in many
tumors including human
breast tumors and stimulates growth of vascular networks that support
tumor growth and
metastasis. We previously reported that natural and
synthetic progestins (P) increased
VEGF mRNA and
protein levels in
progesterone receptor (PR) containing T47-D human
breast cancer cells in a PR dependent manner, but not in PR positive ZR-75 and MCF-7, or in PR negative MDA-MB-231 cells. This indicated that factors beside PR are involved in
progesterone-dependent
VEGF regulation. We, therefore, tested additional tumor cell lines reported to contain PR for
progestin-dependent
VEGF induction. Out of nine PR-positive
breast tumor cell lines,
progestins induced
VEGF in three cell lines that lack wild-type p53 (T47-D, BT-474, and HCC-1428) but not in cell lines that contained the wild-type p53
protein. The T47-D and BT-474 cells express mutant p53, while the p53
protein is absent HCC-1428 cells. The anti-
progestin RU-486 blocked
progestin-dependent induction of
VEGF in T47-D and BT-474 cells but not in HCC-1428 cells. However,
RU-486 partially blocked
medroxyprogesterone acetate-dependent induction of
VEGF in HCC-1428 cells.
Estrogen receptor (ER) and PR agonists and antagonists also induce
VEGF in HCC-1428 cells and this effect was partially blocked by anti-
estrogen ICI-182, 780.
Progestin-dependent
VEGF induction was completely inhibited by PRIMA-1-activated p53 in all cell-types, but
progestin-dependent transcription of a
progesterone-regulated minimal promoter was only partially inhibited.
PRIMA-1 induced activation of p53 in tumor cell lines was confirmed with a p53-responsive p21 reporter plasmid and by detecting increased levels of p21
proteins in cell lysates.
PRIMA-1 induced p53
protein in the HCC-1428 cells while levels of mutant p53
protein in T47-D and BT-474 remained unaltered.
Progestin-dependent induction of
VEGF was also inhibited by stable transfection of wild-type p53 in T47-D cells. These results are consistent with the hypothesis that wild-type p53 blocks
progestin-dependent induction of
VEGF in
breast cancer cells and this may be a novel anti-angiogenic mechanism for controlling the growth of
progestin-dependent
tumors.