Prolactin-inducible EDD E3 ubiquitin ligase promotes TORC1 signalling, anti-apoptotic protein expression, and drug resistance in breast cancer cells

Abstract

Previously, we identified a prolactin (PRL)-inducible gene encoding EDD E3 ubiquitin ligase in human breast cancer (BCa) cells. We reported that EDD binds the mTOR (TORC1)-associated α4 phosphoprotein-PP2Ac protein phosphatase complex that regulates initiation of translation and cell cycle progression, and that EDD targets PP2Ac for proteasomal degradation.

The present study showed that EDD immunostaining was low in benign human breast tissues, but increased progressively in ductal carcinoma in-situ, low-grade, and high-grade BCa, and in triple-negative BCa (TNBC). EDD mRNA and protein levels varied in human BCa cell lines.

In high-EDD expressing MCF-7 and T47D cells, siRNA knockdown of EDD arrested cells in the G2-phase of the cell cycle, decreased cell viability, and increased apoptosis. EDD siRNA-induced apoptosis in MCF-7 cells correlated with significantly increased levels of pro-apoptotic Bim and Bak mRNAs and proteins (P < 0.05, n = 3-6), and increased levels of pro-apoptotic Bax and MOAP-1 proteins (P < 0.001, n = 3-6), leading to increased cleavage of caspase-7 and caspase substrate poly-ADP-ribose polymerase-1 (PARP-1), as compared to control cells.

Loss of EDD in MCF-7 cells decreased PRL-induced phosphorylation of eukaryotic initiation factor 4E-binding protein-1, a mediator of TORC1 signaling, resulting in decreased binding of 4E to γ-aminophenyl-m7GTP agarose in Cap-binding assays. In low-EDD expressing MDA-MB-436 TNBC cell line, gain of EDD following pCMV-Tag2B.EDD transfection increased cell resistance to chemotherapeutic drugs cisplatin and doxorubicin, TORC1 inhibitor rapamycin, and TORC1/TORC2 inhibitor INK128, as compared to controls. In contrast, loss of EDD in MCF-7 cells increased cell sensitivity to cisplatin, doxorubicin, rapamycin, and selective estrogen receptor modulator tamoxifen.

In summary, EDD levels increase with BCa progression in vivo. PRL-inducible EDD in BCa cells promotes TORC1 signaling, anti-apoptotic protein expression, and drug resistance in vitro.

These findings implicate EDD as a potential therapeutic target and support PRL receptor blockade as an additional therapy for BCa.

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See also:

- Official Web Site: The Di Bella Method;

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- The Di Bella Method (A Fixed Part - Somatostatin, Octreotide, Sandostatin LAR, analogues and/or derivatives);

- Somatostatin in oncology, the overlooked evidences - In vitro, review and in vivo publications;

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- Complete objective response, stable for 5 years, with the Di Bella Method, of multiple-metastatic carcinoma of the breast;

- Evaluation of the safety and efficacy of the first-line treatment with somatostatin combined with melatonin, retinoids, vitamin D3, and low doses of cyclophosphamide in 20 cases of breast cancer: a preliminary report;

- The Di Bella Method (DBM) improved survival, objective response and performance status in a retrospective observational clinical study on 122 cases of breast cancer;

- Complete objective response to biological therapy of plurifocal breast carcinoma;

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- Low-grade Non-Hodgkin Lymphoma at Advanced Stage: A Case Successfully Treated With Cyclophosphamide Plus Somatostatin, Bromocriptine, Retinoids, and Melatonin;

- The Di Bella Method (DBM) improved survival, objective response and performance status in a retrospective observational clinical study on 55 cases of Lymphomas;

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