Tumor suppression via inhibition of SWI/SNF complex-dependent NF-κB activation

Abstract

The transcription factor NF-κB is constitutively activated in many epithelial tumors but few NF-κB inhibitors are suitable for cancer therapy because of its broad biological effects. We previously reported that the d4-family proteins (DPF1, DPF2, DPF3a/b) function as adaptor proteins linking NF-κB with the SWI/SNF complex. Here, using epithelial tumor cell lines, A549 and HeLaS3, we demonstrate that exogenous expression of the highly-conserved N-terminal 84-amino acid region (designated “CT1”) of either DPF2 or DPF3a/b has stronger inhibitory effects on anchorage-independent growth than the single knockdown of any d4-family protein. This indicates that CT1 can function as an efficient dominant-negative mutant of the entire d4-family proteins. By in situ proximity ligation assay, CT1 was found to retain full adaptor function, indicating that the C-terminal region of d4-family proteins lacking in CT1 would include essential domains for SWI/SNF-dependent NF-κB activation. Microarray analysis revealed that CT1 suppresses only a portion of the NF-κB target genes, including representative SWI/SNF-dependent genes. Among these genes, IL6 was shown to strongly contribute to anchorage-independent growth. Finally, exogenous CT1 expression efficiently suppressed tumor formation in a mouse xenograft model, suggesting that the d4-family proteins are promising cancer therapy targets.

Single-Cell Analysis of Multiple Steps of Dynamic NF-κB Regulation in Interleukin-1α-Triggered Tumor Cells Using Proximity Ligation Assays

“…Although previous studies used the PLA approach for the validation of protein/protein interactions in the NF-κB system [49,50], a systematic study investigating the dynamic regulation of NF-κB at all levels of gene expression has not yet been performed. This study shows the suitability of PLAs for the quantitative and time-resolved analysis of IL-1α-induced dynamic NF-κB regulation, unravelling further aspects of NF-κB signaling.…”

NFκB dynamics determine the stimulus-specificity of epigenomic reprogramming in macrophages

“…6b), suggesting that they tend to 17 function as cis-acting enhancer elements near key innate immune genes such as Ccl5 (Fig. 3f), which 18 has previously been shown to require chromatin remodeling for full induction 12 . 19 Our model predicted that chromatin accessibility is primarily determined by whether NFκB is 20 oscillatory or non-oscillatory within a single cell.…”

“…2a). 5 However, NFκB is capable of at least transiently interacting with nucleosomal DNA 17 , and can displace 6 nucleosomes in cooperation with pioneer factor Pu.1 2 or remodeling machinery such as SWI/SNF 7 complexes 18 . Furthermore, the DNA-histone interface is not static but is composed of low-affinity 8 interactions that promote spontaneous disassociation or "breathing" 19 .…”

“…4c). 18 Next, we asked whether these NFκB dynamics-dependent enhancers had a functional role in 19 macrophage gene expression. We hypothesized that de novo enhancers would alter transcriptional 20 responses to subsequent stimulation.…”

Epigenetic Targeting of Glioblastoma

“…The tumor suppressor SWI/SNF complex was the first chromatin remodeler discovered, is mutated in more than 20% of the tumors ( 97 , 98 ) and is involved in the maintenance of stemness in glioma cells ( 99 ). The effects of SWI/SNF inactivation can be counteracted by inhibitors of the TK pathway and of NF-kB ( 100 , 101 ); however, as outlined previously, these targeted therapies were unsuccessful in GBM patients. PARP-1 polymerase is involved in chromatin remodeling mechanisms through histone modification and inhibition of the ISWI complex ( 102 ).…”