Inhibition of Expression of the Chromatin Remodeling Gene, SNF2L, Selectively Leads to DNA Damage, Growth Inhibition, and Cancer Cell Death

Abstract

SNF2L, a chromatin remodeling gene expressed in diverse tissues, cancers, and derived cell lines, contributes to the chromatin remodeling complex that facilitates transcription. Because of this wide expression, it has not been exploited as a cancer therapeutic target. However, based on our present studies, we find that cancer cells, although expressing SNF2L at similar levels as their normal counterparts, are sensitive to its knockdown. This is not observed when its imitation SWI ortholog, SNF2H, is inhibited. SNF2L siRNA inhibition using two different siRNAs separately reduced SNF2L transcript levels and protein in both normal and cancer lines, but only the cancer lines showed significant growth inhibition, DNA damage, a DNA damage response, and phosphorylation of checkpoint proteins and marked apoptosis. DNA damage and the damage response preceded apoptosis rather than being consequences of it. The damage response consisted of increased phosphorylation of multiple substrates including ATR, BRCA1, CHK1, CHK2, and H2AX. Both the total and phosphorylated levels of p53 increased. The downstream targets of p53, p21, GADD45A, and 14-3-3σ, were also upregulated. The alterations in checkpoint proteins included increased phosphorylated cdc2 but not Rb, which resulted in a modest G 2 -M arrest. Although apoptosis may be mediated by Apaf-1/caspase 9, other caspases could be involved. Other members of the chromatin remodeling or SWI/SNF gene families exhibited overall reduced levels of expression in the cancer lines compared with the normal lines. This raised the hypothesis that cancers are sensitive to SNF2L knockdown because, unlike their normal counterparts, they lack sufficient compensation from other family members.

Nucleosome Remodeler SNF2L Suppresses Cell Proliferation and Migration and Attenuates Wnt Signaling

“…It is possible, that the SNF2L expression patterns in human and mouse tissues differ, as was previously suggested based on mRNA analyses (53). In this study, the authors found nearly ubiquitous expression of SNF2L in the tested human samples.…”

“…This view is mainly grounded in studies in the murine system. Ye et al previously pointed out differences between the expression patterns in mouse versus human tissues, based on RT-PCRs and expressed sequence tags (ESTs) posted on the NCBI website (53). Taken together, SNF2L expression in humans was solely monitored on the RNA level and not on the protein level.…”

Transcriptomic Profiling of Gametogenesis in Triploid Pacific Oysters Crassostrea gigas: Towards an Understanding of Partial Sterility Associated with Triploidy

“…The probable global transcription activator SNF2L1, encoded by the gene smarca1 , is a helicase thought to regulate transcription of genes by altering the chromatin structure around these genes, suggesting an epigenetic reprogramming to handle triploidy. Expressed in human oocytes [55], inhibition of SNF2L1 leads to DNA damage and growth inhibition [56]. We also observed an upregulation of ig-h3 that is induced by the transforming growth factor beta (TGF-β), the signaling of which is essential for oogenesis [57].…”

Identification of Proteins at Active, Stalled, and Collapsed Replication Forks Using Isolation of Proteins on Nascent DNA (iPOND) Coupled with Mass Spectrometry

“…SNF2H is also recruited to double-strand breaks where it functions to help unfold chromatin (39). Less is known about SNF2L function in DNA damage responses, but silencing SNF2L by RNA interference increases the amount of DNA damage signaling in cells (40). Because iPOND selectively purifies proteins behind the fork in complexes with newly synthesized DNA, our data suggest that SNF2L and SNF2H function on newly deposited chromatin.…”