Is Peripheral Benzodiazepine Receptor (PBR) Gene Expression Involved in Breast Cancer Suppression by Dietary Soybean Protein.

摘要

Localization of PBR in nucleus, and nuclear cholesterol transport are implicated in breast cancer development. Our previous report suggested that the soybean protein may protect against the development of a more aggressive mammary gland adenocarcinoma. Furthermore, there was a delay in the development of breast cancer in the soybean group challenged with DMBA in comparison to the animals fed casein and challenged with DMBA. The objective of the present task was to confirm whether the beneficial effect of soybean protein in breast cancer development is mediated via PERs. Breast cancer was developed by gavage administration of single dose of DMBA (80 mg/kg) into 50-day old female rats, maintained on a standard AIN-76A diet containing either 20% casein or 20% soybean protein. After 122 days of DMBA administration, the animals were sacrificed. All tumors were detected by palpation and at autopsy biopsy specimens were taken for histological grading. The casein group had 20% grade I (non-aggressive), 60% grade II (moderately aggressive) and 20% grade III (aggressive) mammary gland adenocarcinoma. However, the soybean group had 100% grade I adenocarcinoma and no aggressive grade II or grade III. Control animals had no tumor. Bmax of PBRs was significantly higher in cancerous tissues than that in control tissues. However, the increase was significantly less in soybean protein group (53%) than that in casein group (128%). Nuclear cholesterol uptake as well as NTPase activity was significantly higher in cancerous tissues than control tissues. However, while there was no significant change in the cholesterol uptake between casein group and soybean protein group, endogenous cholesterol level was more in casein group than soybean group.