Lian, Jane B.

ABSTRACTMitotic bookmarking is an epigenetic control mechanism that sustains gene expression in progeny cells; it is often found in genes related to the maintenance of cellular phenotype and growth control. RUNX transcription factors regulate a broad spectrum of RNA Polymerase (Pol II) transcribed genes important for lineage commitment but also regulate RNA Polymerase I (Pol I) driven ribosomal gene expression, thus coordinating control of cellular identity and proliferation. In this study, using fluorescence microscopy and biochemical approaches we show that the principal RUNX co‐factor, CBFβ, associates with nucleolar organizing regions (NORs) during mitosis to negatively regulate RUNX‐dependent ribosomal gene expression. Of clinical relevance, we establish for the first time that the leukemogenic fusion protein CBFβ‐SMMHC (smooth muscle myosin heavy chain) also associates with ribosomal genes in interphase chromatin and mitotic chromosomes to promote and epigenetically sustain regulation of ribosomal genes through RUNX factor interactions. Our results demonstrate that CBFβ contributes to the transcriptional regulation of ribosomal gene expression and provide further understanding of the epigenetic role of CBFβ‐SMMHC in proliferation and maintenance of the leukemic phenotype. J. Cell. Biochem. 115: 2155–2164, 2014. © 2014 Wiley Periodicals, Inc.

Understanding the mechanisms that sustain pluripotency in human embryonic stem cells (hESCs) is an active area of research that may prove useful in regenerative medicine and will provide fundamental information relevant to development and cancer. hESCs and cancer cells share the unique ability to proliferate indefinitely and rapidly. Because the protein survivin is uniquely overexpressed in virtually all human cancers and in hESCs, we sought to investigate its role in supporting the distinctive capabilities of these cell types. Results presented here suggest that survivin contributes to the maintenance of pluripotency and that post‐transcriptional control of survivin isoform expression is selectively regulated by microRNAs. miR‐203 has been extensively studied in human tumors, but has not been characterized in hESCs. We show that miR‐203 expression and activity is consistent with the expression and subcellular localization of survivin isoforms that in turn modulate expression of the Oct4 and Nanog transcription factors to sustain pluripotency. This study contributes to understanding of the complex regulatory mechanisms that govern whether hESCs proliferate or commit to lineages. J. Cell. Physiol. 230: 63–70, 2015. © 2014 Wiley Periodicals, Inc.

ABSTRACTThe chromatin remodeling complex SWI/SNF and the transcription factor C/EBPβ play critical roles in osteoblastic cells as they jointly control transcription of a number of bone‐related target genes. The largest C/EBPβ isoform, LAP*, possesses a short additional N‐terminal domain that has been proposed to mediate the interaction of this factor with SWI/SNF in myeloid cells. Here we examine the requirement of a functional N‐terminus in C/EBPβ‐LAP* for binding SWI/SNF and for recruiting this complex to the Ric‐8B gene to mediate transcriptional repression. We find that both C/EBPβ‐LAP* and SWI/SNF simultaneously bind to the Ric‐8B promoter in differentiating osteoblasts that repress Ric‐8B expression. This decreased expression of Ric‐8B is not accompanied by significant changes in histone acetylation at the Ric‐8B gene promoter sequence. A single aminoacid change at the C/EBPβ‐LAP* N‐terminus (R3L) that inhibits C/EBPβ‐LAP*‐SWI/SNF interaction, also prevents SWI/SNF recruitment to the Ric‐8B promoter as well as C/EBPβ‐LAP*‐dependent repression of the Ric‐8B gene. Inducible expression of the C/EBPβ‐LAP*R3L protein in stably transfected osteoblastic cells demonstrates that this mutant protein binds to C/EBPβ‐LAP*‐target promoters and competes with the endogenous C/EBPβ factor. Together our results indicate that a functional N‐terminus in C/EBPβ‐LAP* is required for interacting with SWI/SNF and for Ric‐8B gene repression in osteoblasts. J. Cell. Physiol. 229: 1521–1528, 2014. © 2014 Wiley Periodicals, Inc.

AbstractCore Binding Factor β (CBFβ) is complexed with the RUNX family of transcription factors in the nucleus to support activation or repression of genes related to bone (RUNX2), hematopoiesis (RUNX1) and gastrointestinal (RUNX3) development. Furthermore, RUNX proteins contribute to the onset and progression of different types of cancer. Although CBFβ localizes to cytoskeletal architecture, its biological role in the cytoplasmic compartment remains to be established. Additionally, the function and localization of CBFβ during the cell cycle are important questions relevant to its biological role. Here we show that CBFβ dynamically distributes in different stages of cell division and importantly is present during telophase at the midbody, a temporal structure important for successful cytokinesis. A functional role for CBFβ localization at the midbody is supported by striking defects in cytokinesis that include polyploidy and abscission failure following siRNA‐mediated downregulation of endogenous CBFβ or overexpression of the inv(16) fusion protein CBFβ‐SMMHC. Our results suggest that CBFβ retention in the midbody during cytokinesis reflects a novel function that contributes to epigenetic control. J. Cell. Physiol. 229: 1466–1474, 2014. © 2014 Wiley Periodicals, Inc.

Abstract The regulatory information for phenotype, proliferation, and growth of normal and tumor cells must be maintained through genome replication in the S phase and cell division during mitosis. Epigenetic mechanisms that include DNA methylation, posttranslational modifications of histones, selective utilization of histone variants, and inheritable RNA molecules play pivotal roles in maintaining cellular identity through mitotic divisions. Recent studies demonstrate that mitotic occupancy of genes, which are determinants of cell fate, growth, and proliferation, by lineage-restricted transcription factors is a key epigenetic mechanism for retention and transmission of cellular expression memory. Evidence is emerging for the presence of distinct transcriptional regulatory microenvironments in mitotic chromosomes in which the genes bookmarked for reactivation postmitotically reside. Importantly, some oncoproteins are present in mitotic microenvironments where they occupy target genes during mitosis and may contribute to perpetuating the transformed phenotype. We discuss emerging regulatory implications of epigenetically bookmarking genes during mitosis for physiologic control as well as for the onset and progression of cancer. Cancer Res; 74(2); 420–5. ©2014 AACR.

AbstractRunx2 is the master transcription factor for bone formation. Haploinsufficiency of RUNX2 is the genetic cause of cleidocranial dysplasia (CCD) that is characterized by hypoplastic clavicles and open fontanels. In this study, we found that Pin1, peptidyl prolyl cis–trans isomerase, is a critical regulator of Runx2 in vivo and in vitro. Pin1 mutant mice developed CCD‐like phenotypes with hypoplastic clavicles and open fontanels as found in the Runx2+/− mice. In addition Runx2 protein level was significantly reduced in Pin1 mutant mice. Moreover Pin1 directly interacts with the Runx2 protein in a phosphorylation‐dependent manner and subsequently stabilizes Runx2 protein. In the absence of Pin1, Runx2 is rapidly degraded by the ubiquitin‐dependent protein degradation pathway. However, Pin1 overexpression strongly attenuated uniquitin‐dependent Runx2 degradation. Collectively conformational change of Runx2 by Pin1 is essential for its protein stability and possibly enhances the level of active Runx2 in vivo. J. Cell. Physiol. 228: 2377–2385, 2013. © 2013 Wiley Periodicals, Inc.

AbstractCancer is a multifaceted disease that involves acquisition of genetic mutations, deletions, and amplifications as well as deregulation of epigenetic mechanisms that fine‐tune gene regulation. Key epigenetic mechanisms that include histone modifications, DNA methylation, and non‐coding RNA‐mediated gene silencing are often deregulated in a variety of cancers. Subnuclear localization of key proteins in the interphase nucleus and bookmarking of genes by lineage commitment factors in mitosis—a new dimension to epigenetic control of fundamental biological processes—is also modified in cancer. In this review, we discuss the various aspects of epigenetic control that are operative in a variety of cancers and their potential for risk assessment, early detection, targeted therapy, and personalized medicine. J. Cell. Physiol. 228: 2103–2108, 2013. © 2013 Wiley Periodicals, Inc.

AbstractVorinostat, an oral histone deacetylase inhibitor with antitumor activity, is in clinical trials for hematologic and solid tumors that metastasize and compromise bone structure. Consequently, there is a requirement to establish the effects of vorinostat on tumor growth within bone. Breast (MDA-231) and prostate (PC3) cancer cells were injected into tibias of SCID/NCr mice and the effects of vorinostat on tumor growth and osteolytic disease were assessed by radiography, micro-computed tomography, and histologic and molecular analyses. Vorinostat-treated and control mice without tumors were also examined. Tumor growth in bone was reduced ∼33% by vorinostat with inhibited osteolysis in the first few weeks of the experiment. However, osteolysis became more severe in both the vehicle and vorinostat-treated groups. Vorinostat increased the expression of tumor-derived factors promoting bone resorption, including PTHrP, IL-8, and osteopontin. After 4 weeks of vorinostat therapy, the non–tumor-bearing contralateral femurs and limbs from vorinostat-treated tumor-free SCID mice showed significant bone loss (50% volume density of controls). Thus, our studies indicate that vorinostat effectively inhibits tumor growth in bone, but has a negative systemic effect reducing normal trabecular bone mass. Vorinostat treatment reduces tumor growth in bone and accompanying osteolytic disease as a result of decreased tumor burden in bone. However, vorinostat can promote osteopenia throughout the skeleton independent of tumor cell activity. Mol Cancer Ther; 9(12); 3210–20. ©2010 AACR.