The Yin Yang-1 (YY1) protein undergoes a DNA-replication-associated switch in localization from the cytoplasm to the nucleus at the onset of S phase

Prostaglandin F2alpha suppresses rat steroidogenic acute regulatory protein expression via induction of Yin Yang 1 protein and recruitment of histone deacetylase 1 protein

Prostaglandin F2alpha (PGF2alpha) plays a pivotal role in ovarian luteolysis by inhibiting the expression of steroidogenic acute regulatory (StAR) protein, leading to a decrease in intracellular cholesterol transport and luteal steroid production. Previously we have demonstrated that the transcription factor Yin Yang 1 (YY1) bound to three regions in the StAR promoter in vitro and repressed promoter activity. This study further defined the YY1-mediated PGF2alpha effect on the inhibition of StAR protein expression through YY1 interaction with a single region in the StAR promoter in vivo. PGF2alpha consistently suppressed StAR mRNA and protein expression in cultured luteal cells in a dose-dependent manner. PGF2alpha also enhanced YY1 protein expression and binding to its cis-element in a time-dependent pattern that preceded the decline in StAR protein levels. The StAR promoter region bound by YY1 was also associated with histone deacetylase 1 (HDAC1). PGF2alpha treatment promoted HDAC1 binding to and suppressed the histone H3 acetylation in this region. On the contrary, YY1 knockdown decreased HDAC1 binding, increased histone H3 acetylation, enhanced StAR protein expression, and negated PGF2alpha effect on StAR protein expression. Luciferase assays showed that YY1 overexpression inhibited StAR promoter activity and the addition of a HDAC inhibitor, trichostatin A, abrogated the effect of YY1. Trichostatin A-treated luteal cells displayed increased StAR protein expression. These data indicate that PGF2alpha enhances a direct YY1/StAR promoter interaction and the recruitment of HDAC1 to the promoter, thereby preventing transcriptional activation of the StAR gene.

PIASy-mediated sumoylation of Yin Yang 1 depends on their interaction but not the RING finger

As a multifunctional protein, Yin Yang 1 (YY1) has been demonstrated to regulate both gene expression and protein posttranslational modifications. However, gaps still exist in our knowledge of how YY1 can be modified and what the consequences of its modifications are. Here we report that YY1 protein can be sumoylated both in vivo and in vitro. We have identified lysine 288 as the major sumoylation site of YY1. We also discovered that PIASy, a SUMO E3 ligase, is a novel YY1-interacting protein and can stimulate the sumoylation of YY1 both in vitro and in vivo. Importantly, the effects of PIASy mutants on in vivo YY1 sumoylation correlate with the YY1-PIASy interaction but do not depend on the RING finger domain of PIASy. This regulation is unique to YY1 sumoylation because PIASy-mediated p53 sumoylation still relies on the integrity of PIASy, which is also true of all of the previously identified substrates of PIASy. In addition, PIASy colocalizes with YY1 in the nucleus, stabilizes YY1 in vivo, and differentially regulates YY1 transcriptional activity on different target promoters. This study demonstrates that YY1 is a target of SUMOs and reveals a novel feature of a SUMO E3 ligase in the PIAS family that selectively stimulates protein sumoylation independent of the RING finger domain.

Expression of transcription factor Yin Yang 1 in human osteosarcomas

The transcription factor Yin Yang 1 (YY1) is known to be present in some human cancer cell lines and its expression correlates with immune-mediated apoptosis. By using Western blot analysis, we have shown that the YY1 protein is strongly expressed in human osteosarcoma cells and localised mainly in the nucleus. Moreover, by using immunohistochemistry and RT-PCR techniques, we have analysed the expression of YY1 protein in biopsies from human osteosarcomas. The YY1 protein was not detectable by immunohistochemistry in osteoid tissue. However, its expression was restricted to osteosarcoma tissues. These data were confirmed by densitometric analysis of RT-PCR for YY1 expression. Thus, YY1 gene activation appears to be an early event in the process of osteoblastic transformation and its detection may represent, together with the analysis of other established markers, a useful diagnostic tool in human osteosarcomas.

Multifunctional transcription factor YY1: a therapeutic target in human cancer?

The multifunctional transcription factor Yin Yang 1 (YY1) is a complex protein that has been shown to play pivotal roles in development, differentiation, cellular proliferation and apoptosis. It can act as a transcriptional repressor, an activator, or an initiator element binding protein that directs and initiates transcription of numerous cellular and viral genes. Because the expression and function of YY1 are known to be intimately associated with cell-cycle progression, the physiological significance of YY1 activity has recently been applied to models of cancer biology. Several lines of evidence imply that YY1 expression and/or activation is associated with tumourigenesis, in addition to its regulatory roles in normal biological processes. However, controversial results also raised and indicated that further studies are still needed to piece all of the seemingly contradictory data into a complete picture. On the basis of YY1 regulations and functions, novel drugs and specific treatment strategies may be developed with new therapeutic applications for tumour patients in the future.

Transcriptional and translational regulation of BACE1 expression--implications for Alzheimer's disease

The proteolytical processing of the amyloid precursor protein (APP) gives rise to beta-amyloid peptides, which accumulate in brains of Alzheimer's disease (AD) patients. Different soluble or insoluble higher molecular weight forms of beta-amyloid peptides have been postulated to trigger a complex pathological cascade that may cause synaptic dysfunction, inflammatory processes, neuronal loss, cognitive impairment, and finally the onset of the disease. The generation of beta-amyloid peptides requires the proteolytical cleavage of APP by an aspartyl protease named beta-site APP-cleaving enzyme 1 (BACE1). The expression and enzymatic activity of BACE1 are increased in brains of AD patients. Here we discuss the importance of a number of recently identified transcription factors as well as post-transcriptional modifications and activation of intracellular signaling molecules for the regulation of BACE1 expression in brain. Importantly, some of these factors are known to be involved in the inflammatory and chronic stress responses of the brain, which are compromised during aging. Moreover, recent evidence indicates that beneficial effects of non-steriodal anti-inflammatory drugs on the progression of AD are mediated--at least in part--by effects on the peroxisome proliferator-activated receptor-gamma response element present in the BACE1 promoter. The identification of the cell type-specific expression and activation of NF-kappaB, Sp1 and YY1 transcription factors may provide a basis to specifically interfere with BACE1 expression and, thereby, to lower the concentrations of beta-amyloid peptides, which may prevent neuronal cell loss and cognitive decline in AD patients.

Transcription factor YY1: structure, function, and therapeutic implications in cancer biology

The ubiquitous transcription factor Yin Yang 1 (YY1) is known to have a fundamental role in normal biologic processes such as embryogenesis, differentiation, replication, and cellular proliferation. YY1 exerts its effects on genes involved in these processes via its ability to initiate, activate, or repress transcription depending upon the context in which it binds. Mechanisms of action include direct activation or repression, indirect activation or repression via cofactor recruitment, or activation or repression by disruption of binding sites or conformational DNA changes. YY1 activity is regulated by transcription factors and cytoplasmic proteins that have been shown to abrogate or completely inhibit YY1-mediated activation or repression; however, these mechanisms have not yet been fully elucidated. Since expression and function of YY1 are known to be intimately associated with progression through phases of the cell cycle, the physiologic significance of YY1 activity has recently been applied to models of tumor biology. The majority of the data are consistent with the hypothesis that YY1 overexpression and/or activation is associated with unchecked cellular proliferation, resistance to apoptotic stimuli, tumorigenesis and metastatic potential. Studies involving hematopoetic tumors, epithelial-based tumors, endocrine organ malignancies, hepatocellular carcinoma, and retinoblastoma support this hypothesis. Molecular mechanisms that have been investigated include YY1-mediated downregulation of p53 activity, interference with poly-ADP-ribose polymerase, alteration in c-myc and nuclear factor-kappa B (NF-kappaB) expression, regulation of death genes and gene products, and differential YY1 binding in the presence of inflammatory mediators. Further, recent findings implicate YY1 in the regulation of tumor cell resistance to chemotherapeutics and immune-mediated apoptotic stimuli. Taken together, these findings provide strong support of the hypothesis that YY1, in addition to its regulatory roles in normal biologic processes, may possess the potential to act as an initiator of tumorigenesis and may thus serve as both a diagnostic and prognostic tumor marker; furthermore, it may provide an effective target for antitumor chemotherapy and/or immunotherapy.

Cytoplasmic YY1 is associated with increased smooth muscle-specific gene expression: implications for neonatal pulmonary hypertension

Immediately after birth the adluminal vascular SMCs of the pulmonary elastic arteries undergo transient actin cytoskeletal remodeling as well as cellular de-differentiation and proliferation. Vascular smooth muscle phenotype is regulated by serum response factor, which is itself regulated in part by the negative regulator YY1. We therefore studied the subcellular localization of YY1 in arteries of normal newborn piglets and piglets affected by neonatal pulmonary hypertension. We found that YY1 localization changed during development and that expression of gamma-smooth muscle actin correlated with expression of cytoplasmic rather than nuclear YY1. Analysis of the regulation of YY1 localization in vitro demonstrated that polymerized gamma-actin sequestered EGFP-YY1 in the cytoplasm and that YY1 activation of c-myc promoter activity was inhibited by LIM kinase, which increases actin polymerization. Consistent with these data siRNA-mediated down-regulation of YY1 in C2C12 cells increased SM22-alpha expression and inhibited cell proliferation. Thus, actin polymerization controls subcellular YY1 localization, which contributes to vascular SMC proliferation and differentiation in normal pulmonary artery development. In the absence of actin depolymerization, YY1 does not relocate to the nucleus, and this lack of relocation may contribute to the pathobiology of pulmonary hypertension.

The transcription factor Yin Yang 1 is an activator of BACE1 expression

The beta-site amyloid precursor protein-cleaving enzyme 1 (BACE1) is a prerequisite for the generation of beta-amyloid peptides, the principle constituents of senile plaques in the brains of patients with Alzheimer's disease (AD). BACE1 expression and enzymatic activity are increased in the AD brain, but the regulatory mechanisms of BACE1 expression are largely unknown. Here we show that Yin Yang 1 (YY1), a highly conserved and multifunctional transcription factor, binds to its putative recognition sequence within the BACE1 promoter and stimulates BACE1 promoter activity in rat pheochromocytoma 12 (PC12) cells, rat primary neurones and astrocytes. In rat brain YY1 and BACE1 are widely expressed by neurons, but there was only a minor proportion of neurones that co-expressed YY1 and BACE1, suggesting that YY1 is not required for constitutive neuronal BACE1 expression. Resting astrocytes in the untreated rat brain did not display either YY1 or BACE1 immunoreactivity. When chronically activated, however, astrocytes expressed both YY1 and BACE1 proteins, indicating that YY1 is important for the stimulated BACE1 expression by reactive astrocytes. This is further emphasized by the expression of YY1 and BACE1 by reactive astrocytes in proximity to beta-amyloid plaques in the AD brain. Our observations suggest that interfering with expression, translocation or binding of YY1 to its BACE1 promoter-specific sequence may have therapeutic potential for treating patients with AD.

Hepatitis C virus core protein recruits nucleolar phosphoprotein B23 and coactivator p300 to relieve the repression effect of transcriptional factor YY1 on B23 gene expression

Hepatitis C virus (HCV) core has a pleiotropic effect on various promoters. In this study, we found that the expression of nucleolar phosphoprotein B23 was enhanced in HCV core-expressing cells and, moreover, HCV core interacts directly with the C-terminal end of B23. Using sucrose gradient centrifugation analysis and immunoprecipitation assays, HCV core was found in a large complex containing B23 and its interacting partner transcription factor YY1. Both B23 and HCV core associated with YY1 in the central GA/GK-rich and C-terminal zinc finger domain. These physical interactions between core, B23, and YY1 led to ternary complex formation that was bound to the YY1 response element. In a transient cotransfection experiment, relief of the trans-suppression activity of YY1 on the YY1-response element-driven reporter by core and B23 was found. This is also true when examining the effects of these three constructs on the B23 promoter-driven reporter. Additionally, chromatin immunoprecipitation assays indicated that a transcriptional activation complex consisting of core, together with B23, p300, and YY1, was recruited to the YY1 response element of B23 promoter, and this probably occurred through complex formation between core and these three cellular transcription regulators. This is different from the situation in the absence of core, where YY1 and histone deacetylase 1, but not B23 and p300, were associated on the YY1 element as the transcription repression complex. Together, our results indicate that HCV core can recruit B23 and p300 to relieve the repression effect of YY1 on B23 promoter activity, a property that requires the intrinsic histone acetyltransferase activity of p300. Thus, because these three core-associated cellular transcription regulators have a multitude of cellular interacting proteins and are involved in a versatility of cellular processes, the complex formation described here may partially account for the pleiotropic effects of core protein on gene expression and cellular function in HCV-infected cells.

Decreased expression of the human stem cell marker, Rex-1 (zfp-42), in renal cell carcinoma

The Rex-1 (Zfp-42) gene encodes a zinc finger family transcription factor which is highly expressed in mouse and human embryonic stem cells. It is one of several gene markers used to identify human stem cells. While several organs are known to harbor adult human stem cells, the presence and distribution of stem cells in both the normal and neoplastic adult kidney remains largely unknown. In this study we evaluated Rex-1 mRNA and protein expression in normal and malignant kidney tissue specimens from human patients. Rex-1 mRNA expression was determined using both reverse transcription and real-time PCR. REX1 protein expression was assessed by western analysis and immunohistochemistry, using an affinity-purified, polyclonal antibody to the REX1 protein. We found that 14 of 15 (93%) non-tumor renal parenchymal specimens demonstrated Rex-1 mRNA, compared with 5 of 14 (36%) renal tumors (P < 0.005). REX1 protein expression was detected in 21 of 23 (91%) non-tumor and in 7 of 19 (37%) tumor specimens (P < 0.001). Furthermore, in six of these seven renal tumor specimens where REX1 protein expression was detected, the levels were at least 3-fold lower than those in adjacent, normal kidney tissue. There were no differences in Rex-1 mRNA or protein expression among the various histologic subtypes of renal tumors (clear cell carcinoma, papillary carcinoma, chromophobe carcinoma and oncocytoma). Immunohistochemical staining confirmed the absence of REX1 in three renal tumor specimens (two clear cell and one papillary carcinoma), while the REX1 protein was detected in a small percentage of proximal tubular cells in normal renal tissue. Immunohistochemical staining of another stem cell marker, OCT4, demonstrated a similar pattern of protein expression in a small percentage of normal renal proximal tubular cells. In summary, we were able to detect Rex-1 mRNA and protein expression in over 90% of normal renal parenchymal specimens and we observed a significant reduction in REX1 expression in renal tumor specimens of all histologic subtypes.

Oncogenes as novel targets for cancer therapy (part III): transcription factors

This is the third paper in a four-part serial review on potential therapeutic targeting of oncogenes. The previous parts described the involvement of oncogenes in different aspects of cancer growth and development, and considered the new technologies responsible for the advancement of oncogene identification, target validation, and drug design. Because of such advances, new specific and more efficient therapeutic agents can be developed for cancer. This part of the review continues the exploration of various oncogenes that we have grouped within seven categories: growth factors, tyrosine kinases, intermediate signaling molecules, transcription factors, cell cycle regulators, DNA damage repair genes, and genes involved in apoptosis. Part one discussed growth factors and tyrosine kinases and part two discussed intermediate signaling molecules. This portion of the review covers transcription factors and the various strategies being used to inhibit their expression or decrease their activities.

Bilirubin: a natural inhibitor of vascular smooth muscle cell proliferation

BACKGROUND

Bilirubin, a natural product of heme catabolism by heme oxygenases, was considered a toxic waste product until 1987, when its antioxidant potential was recognized. On the basis of observations that oxidative stress is a potent trigger in vascular proliferative responses, that heme oxygenase-1 is antiatherogenic, and that several studies now show that individuals with high-normal or supranormal levels of plasma bilirubin have a lesser incidence of atherosclerosis-related diseases, we hypothesized that bilirubin would have salutary effects on preventing intimal hyperplasia after balloon injury.

METHODS AND RESULTS

We found less balloon injury-induced neointima formation in hyperbilirubinemic Gunn rats and in wild-type rats treated with biliverdin, the precursor of bilirubin, than in controls. In vitro, bilirubin and biliverdin inhibited serum-driven smooth muscle cell cycle progression at the G1 phase via inhibition of the mitogen-activated protein kinase signal transduction pathways and inhibition of phosphorylation of the retinoblastoma tumor suppressor protein.

CONCLUSIONS

Bilirubin and biliverdin might be potential therapeutics in vascular proliferative disorders.

Prodynorphin transcripts and proteins differentially expressed and regulated in the adult human brain

Transcription from multiple promoters along with alternative mRNA splicing constitutes the basis for cell-specific gene expression and mRNA and protein diversity. The prodynorphin gene (PDYN) gives rise to prodynorphin (PDYN), precursor to dynorphin opioid peptides that regulate diverse physiological functions and are implicated in various neuropsychiatric disorders. Here, we characterized PDYN transcripts and proteins in the adult human brain and studied PDYN processing and intracellular localization in model cell lines. Seven PDYN mRNAs were identified in the human brain; two of the transcripts, FL1 and FL2, encode the full-length PDYN. The dominant, FL1 transcript shows high expression in limbic-related structures such as the nucleus accumbens and amygdala. The second, FL2 transcript is only expressed in few brain structures such as the claustrum and hypothalamus. FL-PDYN was identified for the first time in the brain as the dominant PDYN protein product. Three novel PDYNs expressed from spliced or truncated PDYN transcripts either lack a central segment but are still processed into dynorphins, or are translated into N-terminally truncated proteins. One truncated PDYN is located in the cell nucleus, suggesting a novel nonopioid function for this protein. The complexity of PDYN expression and diversity of its protein products may be relevant for diverse levels of plasticity in adaptive responses for the dynorphin system.

Caspase-dependent regulation and subcellular redistribution of the transcriptional modulator YY1 during apoptosis

The transcriptional regulator Yin Yang 1 (YY1) controls many aspects of cell behavior and is essential for development. We analyzed the fate of YY1 during apoptosis and studied the functional consequences. We observed that this factor is rapidly translocated into the cell nucleus in response to various apoptotic stimuli, including activation of Fas, stimulation by tumor necrosis factor, and staurosporine and etoposide treatment. Furthermore, YY1 is cleaved by caspases in vitro and in vivo at two distinct sites, IATD(12)G and DDSD(119)G, resulting in the deletion of the first 119 amino acids early in the apoptotic process. This activity generates an N-terminally truncated YY1 fragment (YY1Delta119) that has lost its transactivation domain but retains its DNA binding domain. Indeed, YY1Delta119 is no longer able to stimulate gene transcription but interacts with DNA. YY1Delta119 but not the wild-type protein or the caspase-resistant mutant YY1D12A/D119A enhances Fas-induced apoptosis, suggesting that YY1 is involved in a positive feedback loop during apoptosis. Our findings provide evidence for a new mode of regulation of YY1 and define a novel aspect of the involvement of YY1 in the apoptotic process.

Congenic mapping of type 1 diabetes—protective gene(s) in an interval of 4Mb on rat chromosome 6q32

Congenic BB.SHR rats introgressing a segment of SHR chromosome 6 onto BB/OK background showed a reduction of diabetes frequency by 72% compared with BB/OK. To identify underlying gene(s), the introgressed segment was shortened and the expression of seven genes (Yy1, Dlk1/Pref-1, Wd40 repeat, Cdc42, Rtl1, Traf3, and Tnfaip2) was studied in blood and spleen of non-diabetic BB/OK, BB.6S, and SHR males and females at an age of 30, 70, and 90 days. The phenotype of congenic sublines narrowed the diabetes-protective region to 4 Mb. The relative expression of Yy1 and Pref-1 in blood and of Pref-1 in spleen was significantly reduced by 50-90% in male and female BB.6S and SHR compared with BB/OK favouring Yy1 and Pref-1 as candidate genes. All other genes were differently expressed according to gender and strain.

Genetic variation in the multifunctional transcription factor Yy1 and type 1 diabetes mellitus in the BB rat

Spontaneous diabetes in B(io)B(reeding) rats is complex, polygenic, and recessively inherited. Several crossing studies have demonstrated that beside the class II genes of the major histocompatibility complex (MHC, Iddm1) additional non-MHC genes are involved in diabetes development. One of them, Iddm4, was initially mapped on chromosome 6q32. To study the physiologic importance of Iddm4 a congenic BB.SHR rat strain (BB.6S) was established. The BB.6S is characterised by a drastic reduction of diabetes frequency (86 vs. 14%) indicating existence of diabetes protective genes of SHR on the exchanged chromosomal segment. One of the possible diabetes susceptibility candidate genes located within this exchanged region is the multifunctional transcription factor Yin yang 1 (Yy1). Yy1 was therefore sequenced in BB/OK and SHR rats. No genetic variation in exons between BB/OK and SHR was found. However, three single nucleotide polymorphisms (SNPs) were detected in intron 4. To determine the "wild type" allele, intron 4 of several diabetes-resistant inbred rat strains (DA, LEW, BN, and WOKW) and wild rats was sequenced. In addition, a congenic BB/OK strain was established by introgressing the same segment of chromosome 6 (D6Rat184-D6Rat3) of wild rats onto BB/OK background (BB.6W). The sequence analysis showed the SNP pattern of SHR (A/C/C) in all inbred rat strains studied whereas both unrelated wild rats showed the pattern of BB/OK rats (T/G/A). The congenic BB.6W rats developed diabetes in the same extent than BB/OK rats. This finding may support the assumption that the SNP pattern of BB/OK and wild rats favours and that of SHR suppresses diabetes development. Because of strong synteny between rat chromosome 6q32 and human 14q32, Yy1 may be also of interest in human type 1 diabetics showing significant linkage to markers on chromosome 14q32.