Figure 4.

CISAL Represses BRCA1 Transcriptional Activity through Inhibition of GABPA Binding with BRCA1 Promoter

(A) Heatmap of selected TFs from Entrez cancer gene list in four commonly used ENCODE cell lines. Cells are sorted based on their RNA-seq data, and the color indicates whether each TF has binding peaks in the BRCA1 promoter. The TFs are hierarchically clustered using Ward's method.

(B) Distribution of GABPA occupancy frequencies in BRCA1 promoter in five different cancer cell lines and liver tissue based on ChIP-seq database. The most enriched peaks are highlighted.

(C) Motif analysis (motif-counter) showing enriched GABPA motif in BRCA1 promoter and the arrow indicates that the highest score binding sites consistently located in the forward strand, highlighted in panel B.

(D) Representation of CISAL and GABPA binding elements in BRCA1 promoter.

(E) ChIP-qPCR analysis of the GABPA genomic occupancy in the BRCA1 promoter in CAL-27 and SCC-9 cells as indicated. Immunoprecipitated DNA was measured by real-time PCR with primers to amplify the BRCA1 promoter region, including the distal site, or the GAPDH locus as a negative control region.

(F) Luciferase reporter assay demonstrating that GABPA activated BRCA1 promoter activity. CAL-27 cells with stable expression of pGL4.20 empty vector (Vector) and wild-type (wt-GABPA BS) or mutant (mut-GABPA BS) BRCA1-promoter-delivered pGL4.20 vectors were transiently co-transfected with GABPA expressing plasmids and pRL-TK.

(G) Luciferase assay demonstrating that GABPA knockdown inhibits BRCA1 promoter activity in CAL-27 cells.

(H–J) Overexpression of wild-type CISAL but not the mutant CISAL (mut-CISAL) represses BRCA1 expression (H), GABPA occupancy in BRCA1 promoter (I) and BRCA1 transcriptional activity (J) in CAL-27 cells.

(K and L) Knockdown of CISAL increases GABPA occupancy at BRCA1 promoter (K) and BRCA1 promoter activity (L) in CAL-27 cells.

(M) Luciferase assay demonstrating that GABPA overexpression attenuates the inhibition of BRCA1 promoter activity, by enhancing expression of CISAL but not mut-CISAL in CAL-27 cells stably transfected with wild-type BRCA1 promoter, whereas overexpression of CISAL demonstrated no effect on BRCA1 promoter activity when transfected with mutant CISAL-binding sites (mut-CISAL BS), and the luciferase signals were similar in groups transfected with mutant GABPA binding sites (mut-GABPA BS).

***p<0.001 by 2-tailed Student's t test (E) or 1-way ANOVA followed by Dunnett's tests for multiple comparisons (F–M). Data are represented as mean ±SEM.