Prolactin blocks nuclear translocation of VDR by regulating its interaction with BRCA1 in osteosarcoma cells

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Published on Tuesday, 06 February 2018

Abstract

Based on their content of prolactin receptors, osteosarcoma cells were predicted to be responsive to prolactin (PRL), but whether PRL would be beneficial or contribute to pathogenesis was unclear.

1,25(OH)(2) vitamin D(3) [1alpha,25(OH)(2)D(3)] has antiproliferative effects on osteosarcoma cells, and a complex interregulatory situation exists between PRL and 1alpha,25(OH)(2)D(3).

Using osteosarcoma cells, Western blot, real time RT-PCR, and promoter-luciferase assays, we have examined the interaction between PRL and 1alpha,25(OH)(2)D(3) and demonstrated that physiological concentrations of PRL block increased osteocalcin and vitamin D receptor (VDR) expression in response to 1alpha,25(OH)(2)D(3). This blockade was shown to be the result of lack of nuclear accumulation of the VDR in response to 1alpha,25(OH)(2)D(3).

Although inhibition of proteasomic degradation with MG132 had no effect on the VDR itself in a 30-min time frame, it relieved the blockade by PRL. Analysis of ubiquitinated proteins brought down by immunoprecipitation with anti-VDR showed PRL regulation of a 250-kDa protein-VDR complex. P250 was identified as the breast cancer tumor suppressor gene product, BRCA1, by Western blot of the VDR immunoprecipitate and confirmed by immunoprecipitation with anti-BRCA1 and blotting for the VDR in the absence and presence of PRL. Knockdown of BRCA1 inhibited nuclear translocation of the VDR and the ability of 1alpha,25(OH)(2)D(3) to induce the VDR.

This, to our knowledge, is the first demonstration of a role for BRCA1 in nuclear accumulation of a steroid hormone and the first demonstration that PRL has the potential to affect the cell cycle through effects on BRCA1.

 

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See also:

- The Di Bella Method (A Fixed Part - Bromocriptine/Cabergoline);

- Vitamin D (analogues and/or derivatives) and cancer;

- The Di Bella Method (A Fixed Part - Dihydrotachysterol/synthetic Vitamin D3);

- Congenital fibrosarcoma in complete remission with Somatostatin, Retinoids, Vitamin D3, Vitamin E, Vitamin C, Melatonin, Calcium, Chondroitin sulfate associated with low doses of Cyclophosphamide in a 14-year Follow Up;

- The Di Bella Method (DBM) in the treatment of prostate cancer: a preliminary retrospective study of 16 patients and a review of the literature;

- 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.


 

Prolactin blocks nuclear translocation of VDR by regulating its interaction with BRCA1 in osteosarcoma cells - Supplementary Data