An anti-apoptotic protein, BRE, promotes growth of chemically-induced mouse hepatocellular carcinoma

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We have previously reported that BRE, brain and reproductive organ expressed, is significantly overexpressed in human hepatocellular carcinoma (HCC). In addition, the expression levels of BRE correlate positively with histological grades of the tumor. By expressing human BRE transgene specifically in mouse livers, we were able to attenuate Fas-induced acute fulminate hepatitis in the mouse model, TTR-V5-BRE. These observations indicate BRE has anti-apoptotic property in vivo. ⁽¹⁾
 Here we report further our investigation of the role of BRE in HCC. HCC was chemically-induced in the transgenic (TTR-V5-BRE) and non-transgenic littermates, bred with C57BL/6, by intraperitoneal injection of diethylnitosamine (DEN) at 15 days postnatally. At 8 months after injection, the mice were sacrificed, and livers collected for determination of tumor number and maximal size, and for immunohistochemistry. Parts of each liver sample were also dissected visually into tumor and adjacent normal portions for Western Blot analysis of BRE expression. By comparison between the DEN-treated male transgenic mice (n=12) and non-transgenic littermate controls (n=8), we observed significantly increased tumor size shown by the former (p=0.049, Exact Wilcoxon Rank Sum test), with the median tumor size 2-fold larger than the latter. There was, however, no statistically significant difference between tumor numbers of the two groups. Female C57BL/6 mice are known to be less sensitive to DEN-treated carcinogenesis. We observed only 8.3% of the female non-transgenic littermates (n=12) developed DEN-induced HCCs, whereas 20% of female transgenic mice (n=5) developed the malignancy.
 For the paired tumoral and normal liver tissues, increased expression of the mouse endogenous BRE was detected in the former by Western Blot analysis. This observation is comparable with the up-regulation of BRE in human HCC.⁽¹⁾ We further demonstrated that DEN administration has no direct effect on BRE expression, as injection of the chemical did not result in any change in the protein expression level in the livers of 15-day old infant mice or 6-8 weeks adult mice in at least the first week post-injection.
 We have previously reported that BRE is highly expressed in lymphoid organs, such as spleen and thymus, suggesting that lymphocytes may be BRE-positive.⁽¹⁾ As DEN-induced HCC is often accompanied by various degrees of leukocytic infiltration, contribution of these infiltrating cells to the observation of BRE protein up-regulation in the liver tumors was studied using common leukocyte antigen CD45 immunohistochemitry staining. No correlation between incidence of infiltration and the up-regulation of BRE was found.
 Taken together, our results suggest that BRE promotes growth, but not induction of hepatocellular carcinoma.
 (1) BC-L Chan, AK-K Ching, K-F To, JC-K Leung, S Chen, et al. 2007 BRE is an antiapoptotic protein in vivo and overexpressed in human hepatocellular carcinoma Oncogene 27(9):1208-17