| dc.description.abstract | Carboxypeptidase-D (CPD), bound to the plasma membrane, cleaves C-terminal arginine
from extracellular substrates. Arginine is converted to nitric oxide (NO), which can
promote tumour progression. We have previously reported that 17?-estradiol (E2) and
prolactin (PRL) upregulate CPD mRNA/protein levels to increase NO production for the
survival of human breast cancer cells. Androgen also upregulates CPD expression to
increase NO production and survival of prostate cancer cells. The human CPD gene
promoter contains a consensus ?-interferon-activated sequence (GAS) and several
putative androgen response elements (AREs) that could potentially bind PRL-activated
transcription factor Stat5 and the ligand-bound androgen receptor (AR), respectively.
This study investigated regulation of the CPD gene by E2, PRL, and synthetic androgen
R1881, in human MCF-7 and T47D breast cancer cell lines. CPD mRNA and protein
levels were elevated by E2, PRL, and R1881, in a time- and dose-dependent manner.
Upregulation of CPD mRNA by PRL and R1881 was abolished by actinomycin-D,
suggesting transcriptional regulation by these two hormones. E2 acts by increasing CPD
mRNA stability. The 2.0-kbp CPD gene promoter construct, containing a consensus GAS
and three putative AREs, was stimulated by PRL and R1881, but not E2. PRL- and
R1881-stimulated CPD promoter activities were not affected by deletion of ARE-2 and
ARE-3, suggesting that the GAS, and in particular, ARE1, are active hormone response
elements. PRL-stimulated GAS-CPD promoter activity was abolished by the mutation
of GAS ( GAS-CPD, ARE-1 intact). Surprisingly, R1881 was unable to stimulate the
same promoter. However, GAS-CPD promoter activity was restored when PRL and
R1881 were administered together, and further enhanced by ectopic transfection of Stat5,
suggesting cooperativity between Stat5 and the AR. Furthermore, ChIP analysis
confirmed that PRL-activated Stat5 and the liganded AR bound to GAS and ARE- 1,
respectively. In summary, PRL and R1881, acting through Stat5 and AR act in concert to
stimulate CPD gene transcription and expression. E2 stabilizes the CPD mRNA to
maintain CPD mRNA/protein levels. Taken together, our results implicate the
cooperative action of the AR and PRL receptor signalling pathways in breast cancer. | en_US |
