Abstract P1-04-02: The Role of BIK (BCL-2 Interaction Killer) Pro-Apoptotic Gene in Breast Cancer
Authors: Rangaraj A , Ye L , Harding KG , Mansel RE , Jiang WG. 
Published: April 2011

Background: The human BIK (BCL-2 interaction killer) gene is a pro-apoptotic member in the Bcl-2 gene family. The BIK gene encodes a Mr 18,000 protein product, which contains a BH3 domain critical for its pro-apoptotic activities. Bik forms heterodimers with various anti-apoptotic proteins, including Bcl-2 and Bcl-XL, the association of which hinders the function of the anti-apoptotic proteins. Fluorescent in-situ hybridization has established the chromosomal localization of the BIK gene to 22q13.3. Recent evidence also reveals that oestrogen starvation-induced apoptosis of breast cancer cells requires BIK.

Methods: Breast cancer tissues (n = 122) and Normal background tissues (n = 33) were collected post surgery. Q-PCR was performed on these tissues to quantify BIK transcript levels in both tissue samples. For in vitro tests, MDA-MB-231 wild type (WT) cell was transfected with anti-BIK ribozyme transgenes, constructed based on the secondary structure of BIK and specifically targeted human BIK, in order to generate a BIK-knockdown subline. The successful knock down of the gene transcript was then verified with RT-PCR and Quantitative real time PCR (Q-PCR) alongside control MDA-MB-231 WT and MDA-MB-231 pEF cells. Cell functions; cell growth using a colorimetric growth assay and cellular motility using conventional scratch wounding assay were tested. Results: Median BIK levels on the normal background and breast cancer tissues were 0.827 and 1.23 respectively being non-significant on Mann-Whitney U test(p=0.27). Patients with higher histological grade (Grade3) (n=55, median 1.53) and TNM4 (n= 4, median= 9.75) demonstrated relatively higher levels of BIK. Tumours from patients with a poor prognosis (Nottingham prognostic index (NPI)&gt;5.4) (n=15, median=2.54) had higher level of BIK transcripts in comparison with patients with good prognosis (NPI&lt;3.4) (n = 65, Median = 1.010), P&lt;0.05. Overall mean survival for patients with low levels of BIK was 139.1 months and 119.2 months for those with high levels. The disease free survival was 133.5 and 113.2 months for patients with low and high levels of BIK, respectively. In vitro, breast cancer cells MDA MB-231 expressed BIK transcript as shown by both RT-PCR and Q-PCR. The anti-BIK transgene successfully knocked down of BIK transcript in the cells. Using a scratch wounding assay and growth assays, it was shown that there was an increase in the rate of migration and growth in the BIK knockdown cells compared to control cell lines.

Conclusion: BIK is a recognized apoptosis promoting gene in breast cancer. Our cohort of breast cancer patients showed a correlation of increased levels of BIK with advancing disease, which also correlates to the estimated overall and disease free survival times. Together with the results from in vitro tests, it is postulated that BIK played a complex role in breast cancer and that the type of interactions with other apoptosis interaction regulators of BIK may be key in deciding the aggressiveness of breast cancer cells.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P1-04-02.