New insight into the significance of KLF4 PARylation in genome stability, carcinogenesis and therapy (2020)
Figure 6

Figure 6. Mechanistic insights into PARylated KLF4 and PARylation-independent KLF4 in DNA damage response and DNA repair. (A) Depletion of KLF4 directly diminishes the DNA damage-induced p21 expression, resulting in the failure of cell cycle arrest in MDA-MB-231 cells. (B) Abolishment of KLF4 PARylation disrupts KLF4-mediated p21 expression that in turn impairs DNA damage response in MDA-MB-231 cells. (C) p-H3 staining analysis of KLF4+/+, KLF4-/- MEFs, KLF4-/- MEF with transfection of wild-type or KLF4-Zinc 2-YYR/AAA mutation. n=4, p values were labeled in figure, one-way ANOVA assay. (D & E) Abolishment of KLF4 PARylation leads to failure in removing damaged DNA as measured by 53BP1 foci. n=4, p=4.74x10-6 (KLF4WT vs KLF4YYR/AAA), one-way ANOVA assay. (E) Summary of D. (F) Failure of KLF4 PARylation leads to increased aneuploidy population in U2OS cells. n=3, p values were labeled in figure, one-way ANOVA assay. (G) Effect of KLF4 PARylation on NHEJ and HR. Wild-type or KLF4-Zinc 2-YYR/AAA mutant KLF4 were co-transfected with I-SCE construction in U2Os-GFP-EJ5 cells (for NHEJ assay) or U2Os-DR-GFP (for HR assay). n=3, p values were labeled in figure, one-way ANOVA assay. (H-J) The effect of overexpression or knockdown KLF4 on mRNA levels of BRCA1 in KLF4-/- MEF (H), MDA-MB-468 (I) and MDA-MB-231 (J). n=3, p values were labeled in figures, one-way ANOVA assay. (K) Heatmap of BRCA1, P21, Bax expression on U2OS cells with expression of wild-type KLF4 or KLF4-Zinc 2-YYR/AAA mutant as well as KLF4-Zinc 2 (Zinc 2 domain deletion) mutant. No difference of BRCA1 expression was measured between expression of wild-type KLF4 or KLF4-Zinc 2-YYR/AAA mutant, while loss of Zinc domain causes drops of BRCA1 expression levels. (L) In early responsive window (1-2 hours after exposure to γ-radiation), while elevation of wild-type KLF4 enhances the expression levels of p21, disruption of KLF4 PARylation diminishes KLF4-mediated p21 accumulation. Upon DNA damage, no matter PARylation or not, elevation of both wild-type or KLF4-PARylation-deficient mutant leads to BRCA1 accumulation suggesting the KLF4-mediated regulation of BRCA1 is independent of PARP1 in MDA-MB-231 cells. (M) KLF4 physically interacts with BRCA1 upstream promoter region measured by CHIP-PCR. (N) inset, top, schematic diagram of the BRCA1 promoter and relative positions of primer sets used in this study. ChIP analysis at the BRCA1 promoter using KLF4-specific or nonspecific control IgG (α-Gal4) in MDA-MB-231 cells. Shown is the enrichment at positions of the BRCA1 locus relative to the TSS, presented as percent recovery of input. (O) inset, top, schematic diagram of the BRCA1 promoter cloning primer and the alignment of potential KLF4 binding motif on BRCA1 promoter with KLF4 binding motif on p21 and SLC5A6 promoter. Shown is the wild-type (BRCA1-WT) or mutant (BRCA1-AA) BRCA1 promoter luciferase reporter activity when co-transfect with KLF4 plasmids. KLF4 co-transfection promotes BRCA1-WT but not BRCA1-AA promoter reporter transcription. n=3, p=0.018, one-way ANOVA assay. (P) ChIP analysis of KLF4 binding to the BRCA1 promoter in MDA-MB-231 at -.3K positions relative to the TSS in untreated and Olaparib (10µM for 8h) or 5Gy radiation treat cells. No significant difference of KLF4 binds to BRCA1 promoter between untreated and Olaparib or radiation treat cells. n=3, p=0.80, one-way ANOVA assay. (Q) BRCA1 reporter assay in KLF4-/- MEFs, KLF4-/- MEF with transfection of wild-type (KLF4WT) or mutant KLF4 (KLF4YYR/AAA, KLF4C403A and KLF4ΔZinc2). The depleted the zinc domain or mutated zinc finger (KLF4C403A and KLF4ΔZinc2) on KLF4 impairs the KLF4-driven BRCA1 expression, while no effect was observed between wild-type and KLF4YYR/AAA mutant. n=3, p values were labeled in figure, one-way ANOVA assay. (R) HR analysis. U2OS-DR-GFP cells were transfected with I-SceI, BRCA1 and siBRCA1 in KLF4-wild-type and depletion condition, respectively. GFP positive cells representing HR repair rate were measured by flow cytometry 48-72 hour after then. Overexpression of BRCA1 restores the HR efficiency in KLF4 knockdown cells. Data are mean ± SEM; n=3, p values were labeled in figure, one-way ANOVA assay.