Regulation of human BFK

Abstract

Bcl-2 protein family members are critical regulators for apoptosis. Reduced levels of apoptotic Bcl-2 family members are detected in gastrointestinal cancers which are responsible for a considerable part of the deaths from cancer. BFK (Bcl-2 Family Kin) is a novel pro-apoptotic Bcl-2 family member specifically expressed in the human gastrointestinal tract. BFK has the characteristic BH3 domain, which was shown to be essential for the apoptosis inducing activity of pro-apoptotic Bcl-2 family members. In the colon four alternatively spliced isoforms were identified. Human and mouse BFK genes share 70% homology at the DNA level and 68.7% homology at the aminoacid levels. Interestingly, human and mouse BFK genes show distinct expression patterns. To explain these differences, we performed gene evolution analyses on the promoter region as well as coding region of these genes. We found that the human BFK promoter experienced positive selective pressure and acquired a distinct set of repetetive elements and transcription factor binding sites. In this study, we identified several novel transcription factor candidates which may have roles in the transcriptional regulation of human BFK. As transcription factors, PARbZIP family members (especially TEF and NFIL3) regulate BFK upon binding to its promoter region. NFIL3 supresses TEF induced BFK transcription in HCT116 cells. We also studied hormonal regulation of human BFK. Tamoxifen, as a mixed agonist/antagonist of estrogen, upregulates human BFK levels in SW707 cells. We hope this study contributes to a better understanding of Bcl-2 family.