Molecular analysis of green tea polyphenol epigallocatechin-3-gallate inhibition of Her-2/neu signalling in breast cancer.

摘要

Overexpression of Her-2/neu epithelial growth factor receptor 2 (EGFR2) occurs in ∼30% of human breast cancers and correlates inversely with the expression of estrogen receptor alpha (ERalpha). Her-2/neu overexpression indicates poor prognosis and resistance to anti-estrogen therapy. The green tea polyphenol epigallocatechin-3-gallate (EGCG) reduced growth in soft agar and phosphatidylinositol-3-kinase (PI3K)/Akt/NF-kappaB signaling induced by Her-2/neu overexpression in NF639 breast cancer cells via inhibition of Her-2/neu receptor tyrosine phosphorylation. The Forkhead box O transcription factor FOXO3a, whose activity is negatively regulated by Akt, was identified as a key transcriptional regulator of ERalpha. Ectopic expression of FOXO3a induced ERalpha protein levels, promoter activity and signaling. Two major functional Forkhead binding sites were identified in the human ERalpha promoter B. ERalpha expression was reduced by constitutively activated Akt, and induced upon inhibition of PI3K/Akt signaling by EGCG, Celecoxib or molecular inhibitors. To further identify pathways regulated by EGCG, NF639 cells resistant to 40 mug/ml EGCG were established and found to display loss of Her-2/neu receptor tyrosine phosphorylation and high constitutive NF-kappaB activity. Inhibition of NF-kappaB sensitized resistant cells to EGCG-mediated growth inhibition. Microarray analyses were performed on NF639 and carcinogen-transformed D3-1 cells. To date, EGCG-mediated alteration in expression of 14 genes involved in nuclear/cytoplasmic transport, transformation, re-dox signaling and hypoxia response in D3-l cells have been validated by RT-PCR.; Transgenic expression of either the c-Rel NF-kappaB or protein kinase CK2alpha subunit in the mouse mammary gland induced late onset tumors in ∼30% of the animals. CK2 has been shown to enhance NF-kappaB activity and the transformed phenotype of breast cancer cells in vitro. To investigate whether c-Rel and CK2 cooperate in vivo, MMTV-c- rel/CK2alpha bi-transgenic mice were established. A cohort of 37 female mice was followed for 24 months, and 45.9% of the animals developed tumors at an average age of 20.6 months. Pathological examination revealed that the tumors were adenocarcinomas, adenosquamous carcinomas, papillary and glandular adenocarcinomas, keratocanthomas, and squamous cell carcinomas. Thus c-Rel and CK2alpha cooperated to enhance tumor numbers, but not kinetics of tumor formation.