Targeting the SIN3A-PF1 interaction inhibits epithelial to mesenchymal transition and maintenance of a stem cell phenotype in triple negative breast cancer

Abstract

Triple negative breast cancer (TNBC) is characterized by a poorly differentiated phenotype and limited treatment options. Aberrant epigenetics in this subtype represent a potential therapeutic opportunity, but a better understanding of the mechanisms contributing to the TNBC pathogenesis is required. The SIN3 molecular scaffold performs a critical role in multiple cellular processes, including epigenetic regulation, and has been identified as a potential therapeutic target. Using a competitive peptide corresponding to the SIN3 interaction domain of MAD (Tat-SID), we investigated the functional consequences of selectively blocking the paired amphipathic α-helix (PAH2) domain of SIN3. Here, we report the identification of the SID-containing adaptor PF1 as a factor required for maintenance of the TNBC stem cell phenotype and epithelial-to-mesenchymal transition (EMT). Tat-SID peptide blocked the interaction between SIN3A and PF1, leading to epigenetic modulation and transcriptional downregulation of TNBC stem cell and EMT markers. Importantly, Tat-SID treatment also led to a reduction in primary tumor growth and disseminated metastatic disease in vivo. In support of these findings, knockdown of PF1 expression phenocopied treatment with Tat-SID both in vitro and in vivo. These results demonstrate a critical role for a complex containing SIN3A and PF1 in TNBC and provide a rational for its therapeutic targeting.

Blocking the PAH2 domain of Sin3A inhibits tumorigenesis and confers retinoid sensitivity in triple negative breast cancer

“…Consistent with this, short term treatments of MDA-MB-231 cells with 31-mer SID peptide [6] increased the expression of RARβ2 by 1.5-fold after 24 h, 8.6-fold after 72 h and 24-fold after 144 h of treatments (Figure 1A). A significant increase in RARβ2 expression was also observed in mouse TNBC cells, 4T1, treated with SID peptide (Supplementary Figure S1).…”

“…We have previously reported that the chromatin remodeling protein Sin3A is a potential drug target in TNBC [4, 5]. We have developed peptides and small molecule mimetic inhibitors (SMIs) that block protein-protein interactions between the PAH2 domain of Sin3A and Sin3-interaction domain (SID) containing chromatin-associated factors like MAD1 and PF1 [6, 7]. This interference results in basal to luminal differentiation by epigenetic modulation and transcriptional repression of genes that promote epithelial to mesenchymal transition, invasion and stemness [4, 6, 7].…”

“…We have developed peptides and small molecule mimetic inhibitors (SMIs) that block protein-protein interactions between the PAH2 domain of Sin3A and Sin3-interaction domain (SID) containing chromatin-associated factors like MAD1 and PF1 [6, 7]. This interference results in basal to luminal differentiation by epigenetic modulation and transcriptional repression of genes that promote epithelial to mesenchymal transition, invasion and stemness [4, 6, 7]. The potential of SID decoys is further accentuated by their ability to modulate therapeutically targetable signaling pathways, [6, 7] opening the avenue for combinatorial therapies that target specific vulnerabilities and are fundamental for an improved clinical outcome.…”

The Chromatin-Associated Phf12 Protein Maintains Nucleolar Integrity and Prevents Premature Cellular Senescence

“…Reports assessing the biological function of Pf1 point to roles in phosphoinositide signaling (7), nervous system development (8), and the epithelial-to-mesenchymal transition and maintenance of a stem cell phenotype (9). To our knowledge, no comprehensive study elucidating the in vivo function of the Pf1 protein has been conducted so far.…”

Emerging Roles of Epigenetic Regulator Sin3 in Cancer

“…Deleting Sin3 (or reducing its level by RNAi) can have a fundamentally different effect on the function of the residual complex in comparison to interfering with only specific protein interactions of Sin3 proteins. Currently, studies directly addressing this issue in the same model system are lacking but can be valuable in addressing the contrasting results and questionable status of Sin3A as tumor suppressor (in Drosophila MEN2 model; Das et al, 2013) or as oncogene (in human TNBC cell models; Bansal et al, 2015).…”