Sin3B: an essential regulator of chromatin modifications at E2F target promoters during cell cycle withdrawal

The Ink4a/Arf locus operates as a regulator of the circadian clock modulating RAS activity

The mammalian circadian clock and the cell cycle are two major biological oscillators whose coupling influences cell fate decisions. In the present study, we use a model-driven experimental approach to investigate the interplay between clock and cell cycle components and the dysregulatory effects of RAS on this coupled system. In particular, we focus on the Ink4a/Arf locus as one of the bridging clock-cell cycle elements. Upon perturbations by the rat sarcoma viral oncogene (RAS), differential effects on the circadian phenotype were observed in wild-type and Ink4a/Arf knock-out mouse embryonic fibroblasts (MEFs), which could be reproduced by our modelling simulations and correlated with opposing cell cycle fate decisions. Interestingly, the observed changes can be attributed to in silico phase shifts in the expression of core-clock elements. A genome-wide analysis revealed a set of differentially expressed genes that form an intricate network with the circadian system with enriched pathways involved in opposing cell cycle phenotypes. In addition, a machine learning approach complemented by cell cycle analysis classified the observed cell cycle fate decisions as dependent on Ink4a/Arf and the oncogene RAS and highlighted a putative fine-tuning role of Bmal1 as an elicitor of such processes, ultimately resulting in increased cell proliferation in the Ink4a/Arf knock-out scenario. This indicates that the dysregulation of the core-clock might work as an enhancer of RAS-mediated regulation of the cell cycle. Our combined in silico and in vitro approach highlights the important role of the circadian clock as an Ink4a/Arf-dependent modulator of oncogene-induced cell fate decisions, reinforcing its function as a tumour-suppressor and the close interplay between the clock and the cell cycle network.

In mammals, the circadian clock controls the punctual regulation of biological processes, which, in turn, affect physiology and behaviour, allowing for the synchronisation of internal time to environmental light-dark cycles. Malfunctions of the circadian clock are associated with pathological phenotypes including cancer. Given the range of molecular time-dependent processes, including metabolism, DNA repair, and the cell cycle, the clock is hypothesised to act as a tumour suppressor. With the help of mathematical modelling and whole-genome analysis combined with machine learning, we investigated the RAS-dependent dysregulation of the circadian clock. We find that the tumour-suppressor Ink4a/Arf acts as a key mediator of RAS oncogene-induced changes in the circadian system, thereby mediating the interplay between the clock and the cell cycle.

Zebrafish sin3b mutants are viable but have size, skeletal, and locomotor defects

BACKGROUND

The transcriptional co-repressor Sin3 is highly conserved from yeast to vertebrates and has multiple roles controlling cell fate, cell cycle progression, and senescence programming. Sin3 proteins recruit histone deacetylases and other chromatin modifying factors to specific loci through interactions with transcription factors including Myc, Rest, p53 and E2F. Most vertebrates have two Sin3 family members (sin3a and sin3b), but zebrafish have a second sin3a paralogue. In mice, sin3a and sin3b are essential for embryonic development. Sin3b knockout mice show defects in growth as well as bone and blood differentiation.

RESULTS

To study the requirement for Sin3b during development, we disrupted zebrafish sin3b using CRISPR-Cas9, and studied the effects on early development and locomotor behavior.

CONCLUSIONS

Surprisingly, Sin3b is not essential in zebrafish. sin3b mutants show a decrease in fitness, small size, changes to locomotor behavior, and delayed bone development. We did not detect a role for Sin3b in cell proliferation. Our analysis of the sin3b mutant revealed a more nuanced requirement for zebrafish Sin3b than would be predicted from analysis of mutants in other species. Developmental Dynamics 246:946-955, 2017. © 2017 Wiley Periodicals, Inc.

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

Pf1, also known as Phf12 (plant homeodomain [PHD] zinc finger protein 12), is a member of the PHD zinc finger family of proteins. Pf1 associates with a chromatin-interacting protein complex comprised of MRG15, Sin3B, and histone deacetylase 1 (HDAC1) that functions as a transcriptional modulator. The biological function of Pf1 remains largely elusive. We undertook the generation of Pf1 knockout mice to elucidate its physiological role. We demonstrate that Pf1 is required for mid- to late gestation viability. Pf1 inactivation impairs the proliferative potential of mouse embryonic fibroblasts (MEFs) and is associated with a significant decrease in bromodeoxyuridine incorporation; an increase in senescence-associated β-galactosidase (SA-β-Gal) activity, a marker of cellular senescence; and elevated levels of phosphorylated H2AX (γ-H2A.X), a marker associated with DNA double-strand breaks. Analysis of transcripts differentially expressed in wild-type and Pf1-deficient cells revealed the impact of Pf1 in multiple regulatory arms of the ribosome biogenesis pathways. Strikingly, assessment of the morphology of the nucleoli exposed an abnormal nucleolar structure in Pf1-deficient cells. Finally, proteomic analysis of the Pf1-interacting complexes highlighted proteins involved in ribosome biogenesis. Taken together, our data reveal an unsuspected function for the Pf1-associated chromatin complex in the ribosomal biogenesis and senescence pathways.

The chromatin-associated Sin3B protein is required for hematopoietic stem cell functions in mice

Hematopoietic stem cells (HSCs) reside at the top of the hematopoietic hierarchy and are the origin of all blood cells produced throughout an individual's life. The balance between HSC self-renewal and differentiation is maintained by various intrinsic and extrinsic mechanisms. Among these, the molecular pathways that restrict cell cycle progression are critical to the maintenance of functional HSCs. Alterations in the regulation of cell cycle progression in HSCs invariably lead to the development of hematologic malignancies or bone marrow failure syndromes. Here we report that hematopoietic-specific genetic inactivation of Sin3B, an essential component of the mammalian Sin3-histone deacetylase corepressor complex, severely impairs the competitive repopulation capacity of HSCs. Sin3B-deleted HSCs accumulate and fail to properly differentiate following transplantation. Moreover, Sin3B inactivation impairs HSC quiescence and sensitizes mice to myelosuppressive therapy. Together, these results identify Sin3B as a novel and critical regulator of HSC functions.

Emerging Roles of Epigenetic Regulator Sin3 in Cancer

Revolutionizing treatment strategies is an urgent clinical need in the fight against cancer. Recently the scientific community has recognized chromatin-associated proteins as promising therapeutic candidates. However, there is a need to develop more targeted epigenetic inhibitors with less toxicity. Sin3 family is one such target which consists of evolutionary conserved proteins with two paralogues Sin3A and Sin3B. Sin3A/B are global transcription regulators that provide a versatile platform for diverse chromatin-modifying activities. Sin3 proteins regulate key cellular functions that include cell cycle, proliferation, and differentiation, and have recently been implicated in cancer pathogenesis. In this chapter, we summarize the key concepts of Sin3 biology and elaborate the recent advancements in the role of Sin3 proteins in cancer with specific examples in multiple endocrine neoplasia type 2, pancreatic ductal adenocarcinoma, and triple negative breast cancer. Finally, a program to create an integrative approach for screening antitumor agents that target chromatin-associated factors like Sin3 is presented.

Human MageB2 Protein Expression Enhances E2F Transcriptional Activity, Cell Proliferation, and Resistance to Ribotoxic Stress

MageB2 belongs to the melanoma antigen gene (MAGE-I) family of tumor-specific antigens. Expression of this gene has been detected in human tumors of different origins. However, little is known about the protein function and how its expression affects tumor cell phenotypes. In this work, we found that human MageB2 protein promotes tumor cell proliferation in a p53-independent fashion, as observed both in cultured cells and growing tumors in mice. Gene expression analysis showed that MageB2 enhances the activity of E2F transcription factors. Mechanistically, the activation of E2Fs is related to the ability of MageB2 to interact with the E2F inhibitor HDAC1. Cellular distribution of MageB2 protein includes the nucleoli. Nevertheless, ribotoxic drugs rapidly promote its nucleolar exit. We show that MageB2 counteracts E2F inhibition by ribosomal proteins independently of Mdm2 expression. Importantly, MageB2 plays a critical role in impairing cell cycle arrest in response to Actinomycin D. The data presented here support a relevant function for human MageB2 in cancer cells both under cycling and stressed conditions, presenting a distinct functional feature with respect to other characterized MAGE-I proteins.

SIN3 is critical for stress resistance and modulates adult lifespan

Coordinate control of gene activity is critical for fitness and longevity of an organism. The SIN3 histone deacetylase (HDAC) complex functions as a transcriptional repressor of many genes. SIN3-regulated genes include those that encode proteins affecting multiple aspects of mitochondrial function, such as energy production and stress responsiveness, important for health maintenance. Here we used Drosophila melanogaster as a model organism to examine the role of SIN3 in the regulation of fitness and longevity. Adult flies with RNA interference (RNAi) induced knockdown expression of Sin3A have reduced climbing ability; an activity that likely requires fully functional mitochondria. Additionally, compared to wild type, adult Sin3A knockdown flies were more sensitive to oxidative stress. Interestingly, media supplementation with the antioxidant glutathione largely restored fly tolerance to oxidative stress. Although Sin3A knockdown flies exhibited decreased longevity compared to wild type, no significant changes in expression of many well-categorized aging genes were observed. We found, however, that Sin3A knockdown corresponded to a significant reduction in expression of genes encoding proteins involved in the de novo synthesis of glutathione. Taken together, the data support a model whereby SIN3 regulates a gene expression program required for proper mitochondrial function and effective stress response during adulthood.

Bmi-1: At the crossroads of physiological and pathological biology

Bmi-1 is a member of the Polycomb repressor complex 1 that mediates gene silencing by regulating chromatin structure and is indispensable for self-renewal of both normal and cancer stem cells. Despite three decades of research that have elucidated the transcriptional regulation, post-translational modifications and functions of Bmi-1 in regulating the DNA damage response, cellular bioenergetics, and pathologies, the entire potential of a protein with such varied functions remains to be realized. This review attempts to synthesize the current knowledge on Bmi-1 with an emphasis on its role in both normal physiology and cancer. Additionally, since cancer stem cells are emerging as a new paradigm for therapy resistance, the role of Bmi-1 in this perspective is also highlighted. The wide spectrum of malignancies that implicate Bmi-1 as a signature for stemness and oncogenesis also make it a suitable candidate for therapy. Nonetheless, new approaches are vitally needed to further characterize physiological roles of Bmi-1 with the long-term goal of using Bmi-1 as a prognostic marker and a therapeutic target.

The DREAM complex promotes gene body H2A.Z for target repression

The DREAM (DP, Retinoblastoma [Rb]-like, E2F, and MuvB) complex controls cellular quiescence by repressing cell cycle genes. Latorre et al. show that Caenorhabditis elegans DREAM targets have an unusual pattern of high gene body HTZ-1/H2A.Z. In mutants of lin-35, the sole p130/Rb-like gene in C. elegans, DREAM targets have reduced gene body HTZ-1/H2A.Z and increased expression. Consistent with a repressive role for gene body H2A.Z, many DREAM targets are up-regulated in htz-1/H2A.Z mutants.

The DREAM (DP, Retinoblastoma [Rb]-like, E2F, and MuvB) complex controls cellular quiescence by repressing cell cycle genes, but its mechanism of action is poorly understood. Here we show that Caenorhabditis elegans DREAM targets have an unusual pattern of high gene body HTZ-1/H2A.Z. In mutants of lin-35, the sole p130/Rb-like gene in C. elegans, DREAM targets have reduced gene body HTZ-1/H2A.Z and increased expression. Consistent with a repressive role for gene body H2A.Z, many DREAM targets are up-regulated in htz-1/H2A.Z mutants. Our results indicate that the DREAM complex facilitates high gene body HTZ-1/H2A.Z, which plays a role in target gene repression.

Sin3b interacts with Myc and decreases Myc levels

Myc expression is deregulated in many human cancers. A yeast two-hybrid screen has revealed that the transcriptional repressor Sin3b interacts with Myc protein. Endogenous Myc and Sin3b co-localize and interact in the nuclei of human and rat cells, as assessed by co-immunoprecipitation, immunofluorescence, and proximity ligation assay. The interaction is Max-independent. A conserved Myc region (amino acids 186-203) is required for the interaction with Sin3 proteins. Histone deacetylase 1 is recruited to Myc-Sin3b complexes, and its deacetylase activity is required for the effects of Sin3b on Myc. Myc and Sin3a/b co-occupied many sites on the chromatin of human leukemia cells, although the presence of Sin3 was not associated with gene down-regulation. In leukemia cells and fibroblasts, Sin3b silencing led to Myc up-regulation, whereas Sin3b overexpression induced Myc deacetylation and degradation. An analysis of Sin3b expression in breast tumors revealed an association between low Sin3b expression and disease progression. The data suggest that Sin3b decreases Myc protein levels upon Myc deacetylation. As Sin3b is also required for transcriptional repression by Mxd-Max complexes, our results suggest that, at least in some cell types, Sin3b limits Myc activity through two complementary activities: Mxd-dependent gene repression and reduction of Myc levels.

A TRIP230-retinoblastoma protein complex regulates hypoxia-inducible factor-1α-mediated transcription and cancer cell invasion

Localized hypoxia in solid tumors activates transcriptional programs that promote the metastatic transformation of cells. Like hypoxia-inducible hyper-vascularization, loss of the retinoblastoma protein (Rb) is a trait common to advanced stages of tumor progression in many metastatic cancers. However, no link between the role of Rb and hypoxia-driven metastatic processes has been established. We demonstrated that Rb is a key mediator of the hypoxic response mediated by HIF1α/β, the master regulator of the hypoxia response, and its essential co-activator, the thyroid hormone receptor/retinoblastoma-interacting protein (TRIP230). Furthermore, loss of Rb unmasks the full co-activation potential of TRIP230. Using small inhibitory RNA approaches in vivo, we established that Rb attenuates the normal physiological response to hypoxia by HIF1α. Notably, loss of Rb results in hypoxia-dependent biochemical changes that promote acquisition of an invasive phenotype in MCF7 breast cancer cells. In addition, Rb is present in HIF1α-ARNT/HIF1β transcriptional complexes associated with TRIP230 as determined by co-immuno-precipitation, GST-pull-down and ChIP assays. These results demonstrate that Rb is a negative modulator of hypoxia-regulated transcription by virtue of its direct effects on the HIF1 complex. This work represents the first link between the functional ablation of Rb in tumor cells and HIF1α-dependent transcriptional activation and invasion.

Senescence-associated SIN3B promotes inflammation and pancreatic cancer progression

Pancreatic ductal adenocarcinoma (PDAC) is strikingly resistant to conventional therapeutic approaches. We previously demonstrated that the histone deacetylase-associated protein SIN3B is essential for oncogene-induced senescence in cultured cells. Here, using a mouse model of pancreatic cancer, we have demonstrated that SIN3B is required for activated KRAS-induced senescence in vivo. Surprisingly, impaired senescence as the result of genetic inactivation of Sin3B was associated with delayed PDAC progression and correlated with an impaired inflammatory response. In murine and human pancreatic cells and tissues, levels of SIN3B correlated with KRAS-induced production of IL-1α. Furthermore, evaluation of human pancreatic tissue and cancer cells revealed that Sin3B was decreased in control and PDAC samples, compared with samples from patients with pancreatic inflammation. These results indicate that senescence-associated inflammation positively correlates with PDAC progression and suggest that SIN3B has potential as a therapeutic target for inhibiting inflammation-driven tumorigenesis.

Identification of genetic suppressors of the Sin3A knockdown wing phenotype

The role of the Sin3A transcriptional corepressor in regulating the cell cycle is established in various metazoans. Little is known, however, about the signaling pathways that trigger or are triggered by Sin3A function. To discover genes that work in similar or opposing pathways to Sin3A during development, we have performed an unbiased screen of deficiencies of the Drosophila third chromosome. Additionally, we have performed a targeted loss of function screen to identify cell cycle genes that genetically interact with Sin3A. We have identified genes that encode proteins involved in regulation of gene expression, signaling pathways and cell cycle that can suppress the curved wing phenotype caused by the knockdown of Sin3A. These data indicate that Sin3A function is quite diverse and impacts a wide variety of cellular processes.

Regulation of oncogene-induced cell cycle exit and senescence by chromatin modifiers

Oncogene activation leads to dramatic changes in numerous biological pathways controlling cellular division, and results in the initiation of a transcriptional program that promotes transformation. Conversely, it also triggers an irreversible cell cycle exit called cellular senescence, which allows the organism to counteract the potentially detrimental uncontrolled proliferation of damaged cells. Therefore, a tight transcriptional control is required at the onset of oncogenic signal, coordinating both positive and negative regulation of gene expression. Not surprisingly, numerous chromatin modifiers contribute to the cellular response to oncogenic stress. While these chromatin modifiers were initially thought of as mere mediators of the cellular response to oncogenic stress, recent studies have uncovered a direct and specific regulation of chromatin modifiers by oncogenic signals. We review here the diverse functions of chromatin modifiers in the cellular response to oncogenic stress, and discuss the implications of these findings on the regulation of cell cycle progression and proliferation by activated oncogenes.

Sin3 interacts with Foxk1 and regulates myogenic progenitors

We have previously reported Foxk1 as an important transcription factor in the myogenic progenitors. SWI-independent-3 (Sin3) has been identified as a Foxk1 binding candidate using a yeast two-hybrid screen. In the present study, we have identified the Foxk1 N-terminal (1-40) region as the Sin3 interacting domain (SID), and the PAH2 of Sin3 as the Foxk1 binding domain utilizing yeast two-hybrid and GST pull-down assays. Further studies revealed that knockdown of Sin3a or Sin3b results in cell cycle arrest and upregulation of cell cycle inhibitor genes. In summary, our present studies have shown that Foxk1 interacts with Sin3 through the SID and that Sin3 has an important role in the regulation of cell cycle kinetics of the MPC population. The results of these studies continue to define and assemble the networks that regulate the MPCs and muscle regeneration.

Tumor suppressor protein p53 recruits human Sin3B/HDAC1 complex for down-regulation of its target promoters in response to genotoxic stress

Master regulator protein p53, popularly known as the “guardian of genome” is the hub for regulation of diverse cellular pathways. Depending on the cell type and severity of DNA damage, p53 protein mediates cell cycle arrest or apoptosis, besides activating DNA repair, which is apparently achieved by regulation of its target genes, as well as direct interaction with other proteins. p53 is known to repress target genes via multiple mechanisms one of which is via recruitment of chromatin remodelling Sin3/HDAC1/2 complex. Sin3 proteins (Sin3A and Sin3B) regulate gene expression at the chromatin-level by serving as an anchor onto which the core Sin3/HDAC complex is assembled. The Sin3/HDAC co-repressor complex can be recruited by a large number of DNA-binding transcription factors. Sin3A has been closely linked to p53 while Sin3B is considered to be a close associate of E2Fs. The theme of this study was to establish the role of Sin3B in p53-mediated gene repression. We demonstrate a direct protein-protein interaction between human p53 and Sin3B (hSin3B). Amino acids 1–399 of hSin3B protein are involved in its interaction with N-terminal region (amino acids 1–108) of p53. Genotoxic stress induced by Adriamycin treatment increases the levels of hSin3B that is recruited to the promoters of p53-target genes (HSPA8, MAD1 and CRYZ). More importantly recruitment of hSin3B and repression of the three p53-target promoters upon Adriamycin treatment were observed only in p53^+/+ cell lines. Additionally an increased tri-methylation of the H3K9 residue at the promoters of HSPA8 and CRYZ was also observed following Adriamycin treatment. The present study highlights for the first time the essential role of Sin3B as an important associate of p53 in mediating the cellular responses to stress and in the transcriptional repression of genes encoding for heat shock proteins or proteins involved in regulation of cell cycle and apoptosis.

A novel mammalian complex containing Sin3B mitigates histone acetylation and RNA polymerase II progression within transcribed loci

Transcription requires the progression of RNA polymerase II (RNAP II) through a permissive chromatin structure. Recent studies of Saccharomyces cerevisiae have demonstrated that the yeast Sin3 protein contributes to the restoration of the repressed chromatin structure at actively transcribed loci. Yet, the mechanisms underlying the restoration of the repressive chromatin structure at transcribed loci and its significance in gene expression have not been investigated in mammals. We report here the identification of a mammalian complex containing the corepressor Sin3B, the histone deacetylase HDAC1, Mrg15, and the PHD finger-containing Pf1 and show that this complex plays important roles in regulation of transcription. We demonstrate that this complex localizes at discrete loci approximately 1 kb downstream of the transcription start site of transcribed genes, and this localization requires both Pf1's and Mrg15's interaction with chromatin. Inactivation of this mammalian complex promotes increased RNAP II progression within transcribed regions and subsequent increased transcription. Our results define a novel mammalian complex that contributes to the regulation of transcription and point to divergent uses of the Sin3 protein homologues throughout evolution in the modulation of transcription.

Small molecule regulators of Rb-E2F pathway as modulators of transcription

The retinoblastoma tumor suppressor protein, Rb, plays a major role in the regulation of mammalian cell cycle progression. It has been shown that Rb function is essential for the proper modulation of G1/S transition and inactivation of Rb contributes to deregulated cell proliferation. Rb exerts its cell cycle regulatory functions mainly by targeting the E2F family of transcription factors and Rb has been shown to physically interact with E2Fs 1, 2 and 3, repressing their transcriptional activity. Multiple genes involved in DNA synthesis and cell cycle progression are regulated by E2Fs, and Rb prevents their expression by inhibiting E2F activity, inducing growth arrest. It has been established that inactivation of Rb by phosphorylation, mutation, or by the interaction of viral oncoproteins leads to a release of the repression of E2F activity, facilitating cell cycle progression. Rb-mediated repression of E2F activity involves the recruitment of a variety of transcriptional co-repressors and chromatin remodeling proteins, including histone deacetylases, DNA methyltransferases and Brg1/Brm chromatin remodeling proteins. Inactivation of Rb by sequential phosphorylation events during cell cycle progression leads to a dissociation of these co-repressors from Rb, facilitating transcription. It has been found that small molecules that prevent the phosphorylation of Rb prevent the dissociation of certain co-repressors from Rb, especially Brg1, leading to the maintenance of Rb-mediated transcriptional repression and cell cycle arrest. Such small molecules have anti-cancer activities and will also act as valuable probes to study chromatin remodeling and transcriptional regulation.

Loss of the SIN3 transcriptional corepressor results in aberrant mitochondrial function

BACKGROUND

SIN3 is a transcriptional repressor protein known to regulate many genes, including a number of those that encode mitochondrial components.

RESULTS

By monitoring RNA levels, we find that loss of SIN3 in Drosophila cultured cells results in up-regulation of not only nuclear encoded mitochondrial genes, but also those encoded by the mitochondrial genome. The up-regulation of gene expression is accompanied by a perturbation in ATP levels in SIN3-deficient cells, suggesting that the changes in mitochondrial gene expression result in altered mitochondrial activity. In support of the hypothesis that SIN3 is necessary for normal mitochondrial function, yeast sin3 null mutants exhibit very poor growth on non-fermentable carbon sources and show lower levels of ATP and reduced respiration rates.

CONCLUSIONS

The findings that both yeast and Drosophila SIN3 affect mitochondrial activity suggest an evolutionarily conserved role for SIN3 in the control of cellular energy production.

Sin3B expression is required for cellular senescence and is up-regulated upon oncogenic stress

Serial passage of primary mammalian cells or strong mitogenic signals induce a permanent exit from the cell cycle called senescence. A characteristic of senescent cells is the heterochromatinization of loci encoding pro-proliferative genes, leading to their transcriptional silencing. Senescence is thought to represent a defense mechanism against uncontrolled proliferation and cancer. Consequently, genetic alterations that allow senescence bypass are associated with susceptibility to oncogenic transformation. We show that fibroblasts genetically inactivated for the chromatin-associated Sin3B protein are refractory to replicative and oncogene-induced senescence. Conversely, overexpression of Sin3B triggers senescence and the formation of senescence-associated heterochromatic foci. Although Sin3B is strongly up-regulated upon oncogenic stress, decrease in expression of Sin3B is associated with tumor progression in vivo, suggesting that expression of Sin3B may represent a barrier against transformation. Together, these results underscore the contribution of senescence in tumor suppression and suggest that expression of chromatin modifiers is modulated at specific stages of cellular transformation. Consequently, these findings suggest that modulation of Sin3B-associated activities may represent new therapeutic opportunities for treatment of cancers.

Sin3: master scaffold and transcriptional corepressor

Sin3 was isolated over two decades ago as a negative regulator of transcription in budding yeast. Subsequent research has established the protein as a master transcriptional scaffold and corepressor capable of transcriptional silencing via associated histone deacetylases (HDACs). The core Sin3-HDAC complex interacts with a wide variety of repressors and corepressors, providing flexibility and expanded specificity in modulating chromatin structure and transcription. As a result, the Sin3/HDAC complex is involved in an array of biological and cellular processes, including cell cycle progression, genomic stability, embryonic development, and homeostasis. Abnormal recruitment of this complex or alteration of its enzymatic activity has been implicated in neoplastic transformation.