Association between weight gain following smoking cessation and development of hypertension in the future.

Although quitting smoking lowers the risk of developing chronic conditions, it usually leads to weight gain. Literature on the association between weight gain after quitting smoking and the future development of hypertension is scarce. Among 234 596 individuals who visited our health center, 856 who had quit smoking for whom data were available at least 6 years after smoking cessation were included. We evaluated changes in blood pressure and antihypertensive drug prescription rate at 1 and 6 years after smoking cessation. We also compared weight and blood pressure between the smoking cessation and continued smoking groups after 6 years. Multiple regression analyses were performed to identify predictors of changes in systolic and diastolic blood pressures using covariates affecting blood pressure. Since a median weight gain of 1.8 kg was observed at 1 year after smoking cessation, we divided the participants into high and low-weight gain groups. No significant intergroup difference in the antihypertensive drug prescription rate was observed after 6 years. The high weight gain group showed significant increases in systolic and diastolic blood pressures after 6 years. Multiple regression analyses revealed that systolic blood pressure was affected by age and high weight gain, while diastolic blood pressure was affected by high weight gain. Our findings suggest that weight gain following smoking cessation leads to blood pressure elevation: the smoking cessation group gained more weight and had higher blood pressure than the continued smoking group. Therefore, weight loss guidance may be useful for individuals who want to quit smoking. Participants in the high weight gain group showed significant increases in systolic and diastolic blood pressures at 6 years after smoking cessation that were significantly different from those observed in participants in the low weight gain group and the continued smoking group.

Absence of first-pass isolation is associated with poor pulmonary vein isolation durability and atrial fibrillation ablation outcomes.

BACKGROUND: Pulmonary vein (PV) reconnection is the main cause of atrial fibrillation (AF) recurrence. This study aimed to examine the effect of first-pass PV isolation (PVI) on PV reconnection frequency during the procedure and on AF ablation outcomes. METHODS: This retrospective study included 446 patients with drug-refractory AF (370 men, aged 64 ± 10 years) who underwent initial PVI using an open-irrigated contact force catheter between January 2015 and October 2016. We investigated the effect of first-pass PVI on PV reconnection during spontaneous PV reconnection and dormant conduction after an adenosine triphosphate challenge. RESULTS: First-pass PVI was achieved in 69% (617/892) of ipsilateral PVs, of which we observed PV reconnection during the procedure in 134 (22%) PVs. This value was significantly lower than that observed in those without first-pass PVI (50%, 138/275) (P < .0001). We divided the subjects into two groups based on the presence or absence of first-pass PVI in at least one of two ipsilateral PVs: first-pass (n = 383, 86%) and non-first-pass groups (n = 63, 14%). The 2-year AF recurrence-free rate was significantly higher in the first-pass group than in the other group (75% vs 59%, log-rank P = .032). In 78 patients with repeat AF ablation, the PV reconnection rate in the second procedure was significantly lower in PVs that had first-pass isolation in the first procedure (34% vs 73%, P < .0001). CONCLUSIONS: Absence of first-pass PVI was associated with a higher frequency of spontaneous PV reconnection and dormant conduction and poor ablation outcomes. First-pass isolation may be a useful marker for better PVI durability.

c-Src promotes tumor progression through downregulation of microRNA-129-1-3p.

MicroRNAs (miRNAs) fine-tune cellular signaling by regulating expression of signaling proteins, and aberrant expression of miRNAs is observed in many cancers. The tyrosine kinase c-Src is upregulated in various human cancers, but the molecular mechanisms underlying c-Src-mediated tumor progression remain unclear. In previous investigations of miRNA-mediated control of c-Src-related oncogenic pathways, we identified miRNAs that were downregulated in association with c-Src transformation and uncovered the signaling networks by predicting their target genes, which might act cooperatively to control tumor progression. Here, to further elucidate the process of cell transformation driven by c-Src, we analyzed the expression profiles of miRNAs in a doxycycline-inducible Src expression system. We found that miRNA (miR)-129-1-3p was downregulated in the early phase of c-Src-induced cell transformation, and that reexpression of miR-129-1-3p disrupted c-Src-induced cell transformation. In addition, miR-129-1-3p downregulation was tightly associated with tumor progression in human colon cancer cells/tissues. Expression of miR-129-1-3p in human colon cancer cells caused morphological changes and suppressed tumor growth, cell adhesion, and invasion. We also identified c-Src and its critical substrate Fer, and c-Yes, a member of the Src family of kinases, as novel targets of miR-129-1-3p. Furthermore, we found that miR-129-1-3p-mediated regulation of c-Src/Fer and c-Yes is important for controlling cell adhesion and invasion. Downregulation of miR-129-1-3p by early activation of c-Src increases expression of these target genes and synergistically promotes c-Src-related oncogenic signaling. Thus, c-Src-miR-129-1-3p circuits serve as critical triggers for tumor progression in many human cancers that harbor upregulation of c-Src.

Comparison of the Safety and Efficacy of Automated Annotation-Guided Radiofrequency Ablation and 2nd-Generation Cryoballoon Ablation in Paroxysmal Atrial Fibrillation.

BACKGROUND: Automated ablation lesion annotation with optimal settings for parameters including contact force (CF) and catheter stability may be effective for achieving durable pulmonary vein isolation. Methods and Results: We retrospectively examined 131 consecutive patients who underwent initial catheter ablation (CA) for paroxysmal atrial fibrillation (PAF) by automatic annotation system (VISITAG module)-guided radiofrequency CA (RFCA) (n=61) and 2nd-generation cryoballoon ablation (CBA) (n=70) in terms of safety and long-term efficacy. The automatic annotation criteria for the RFCA group were as follows: catheter stability range of motion ≤1.5 mm, duration ≥5 s, and CF ≥5 g. We ablated for >20 s with a force-time integral >150 gs at each site, before moving to the next site. Each interlesion distance was <6 mm. Procedural complications were more frequent in the CBA group (1.6% vs. 10.0%, P=0.034). Across a median follow-up of 2.98 years, 88.5% and 70.0% of patients in the RFCA and CBA groups, respectively, were free from recurrence (log-rank test, P=0.0039). There was also a significant difference in favor of RFCA with respect to repeat ablations (3.3% vs. 24.3%, log-rank test, P=0.0003). CONCLUSIONS: RF ablation guided by an automated algorithm that includes CF and catheter stability parameters showed better long-term outcomes than CBA in the treatment of patients with PAF without increasing complications.

Tysnd1 deficiency in mice interferes with the peroxisomal localization of PTS2 enzymes, causing lipid metabolic abnormalities and male infertility.

Peroxisomes are subcellular organelles involved in lipid metabolic processes, including those of very-long-chain fatty acids and branched-chain fatty acids, among others. Peroxisome matrix proteins are synthesized in the cytoplasm. Targeting signals (PTS or peroxisomal targeting signal) at the C-terminus (PTS1) or N-terminus (PTS2) of peroxisomal matrix proteins mediate their import into the organelle. In the case of PTS2-containing proteins, the PTS2 signal is cleaved from the protein when transported into peroxisomes. The functional mechanism of PTS2 processing, however, is poorly understood. Previously we identified Tysnd1 (Trypsin domain containing 1) and biochemically characterized it as a peroxisomal cysteine endopeptidase that directly processes PTS2-containing prethiolase Acaa1 and PTS1-containing Acox1, Hsd17b4, and ScpX. The latter three enzymes are crucial components of the very-long-chain fatty acids ß-oxidation pathway. To clarify the in vivo functions and physiological role of Tysnd1, we analyzed the phenotype of Tysnd1(-/-) mice. Male Tysnd1(-/-) mice are infertile, and the epididymal sperms lack the acrosomal cap. These phenotypic features are most likely the result of changes in the molecular species composition of choline and ethanolamine plasmalogens. Tysnd1(-/-) mice also developed liver dysfunctions when the phytanic acid precursor phytol was orally administered. Phyh and Agps are known PTS2-containing proteins, but were identified as novel Tysnd1 substrates. Loss of Tysnd1 interferes with the peroxisomal localization of Acaa1, Phyh, and Agps, which might cause the mild Zellweger syndrome spectrum-resembling phenotypes. Our data established that peroxisomal processing protease Tysnd1 is necessary to mediate the physiological functions of PTS2-containing substrates.

Relationship between clinical outcomes and unintentional pulmonary vein isolation during substrate ablation of atrial fibrillation guided solely by complex fractionated atrial electrogram mapping.

BACKGROUND: Controversy exists as to whether atrial fibrillation (AF) ablation guided solely by complex fractionated atrial electrogram (CFAE) has a good outcome despite not requiring pulmonary vein isolation (PVI). OBJECTIVES: The purpose of this study was to evaluate the effectiveness of AF ablation guided solely by targeting CFAE areas, and to determine whether its clinical efficacy has any relationship with unintentionally isolating the PV. METHODS: We studied 100 consecutive patients (ages 59 ± 11 years; 54 with paroxysmal, 35 persistent, and 11 long-standing persistent AF), who underwent CFAE-ablation. PV potential (PVP) was recorded before and after ablation. After excluding 39 patients in whom sinus rhythm could not be maintained before ablation by internal cardioversion and/or who had a history of PVI(s), PVPs were analyzed. RESULTS: AF was terminated during ablation in 98% of paroxysmal, 80% of persistent, and 55% of long-standing persistent AF patients. Nifekalant (0.3-0.6 mg/kg) was administered in 30%, 57%, and 83%, respectively. The common areas of CFAE around the PVs were anterior to the right PVs, posterior to the left PVs, and at the ridge of the left atrial appendage. Among 215 PVs in 61 patients (42 paroxysmal, 19 persistent), only 17 PVs (8%) were unintentionally isolated. The atrial potential to PVP was prolonged (>30 ms) in 13% of PVs. After at least 12 months of follow-up (23 ± 5 months), 65% of paroxysmal (11% with drug), 54% of persistent (37% with drug), and 45% of long-standing (60% with drug) AF patients were free from atrial arrhythmia after one session. CONCLUSIONS: CFAE-ablation terminates AF without isolating PVs in a high percentage of patients, and yields excellent clinical outcomes.

Id4, a new candidate gene for senile osteoporosis, acts as a molecular switch promoting osteoblast differentiation.

Excessive accumulation of bone marrow adipocytes observed in senile osteoporosis or age-related osteopenia is caused by the unbalanced differentiation of MSCs into bone marrow adipocytes or osteoblasts. Several transcription factors are known to regulate the balance between adipocyte and osteoblast differentiation. However, the molecular mechanisms that regulate the balance between adipocyte and osteoblast differentiation in the bone marrow have yet to be elucidated. To identify candidate genes associated with senile osteoporosis, we performed genome-wide expression analyses of differentiating osteoblasts and adipocytes. Among transcription factors that were enriched in the early phase of differentiation, Id4 was identified as a key molecule affecting the differentiation of both cell types. Experiments using bone marrow-derived stromal cell line ST2 and Id4-deficient mice showed that lack of Id4 drastically reduces osteoblast differentiation and drives differentiation toward adipocytes. On the other hand knockdown of Id4 in adipogenic-induced ST2 cells increased the expression of Ppargamma2, a master regulator of adipocyte differentiation. Similar results were observed in bone marrow cells of femur and tibia of Id4-deficient mice. However the effect of Id4 on Ppargamma2 and adipocyte differentiation is unlikely to be of direct nature. The mechanism of Id4 promoting osteoblast differentiation is associated with the Id4-mediated release of Hes1 from Hes1-Hey2 complexes. Hes1 increases the stability and transcriptional activity of Runx2, a key molecule of osteoblast differentiation, which results in an enhanced osteoblast-specific gene expression. The new role of Id4 in promoting osteoblast differentiation renders it a target for preventing the onset of senile osteoporosis.

Development of a rapid culture method to induce adipocyte differentiation of human bone marrow-derived mesenchymal stem cells.

Human mesenchymal stem cells (hMSCs) derived from bone marrow are multipotent stem cells that can regenerate mesenchymal tissues such as adipose, bone or muscle. It is thought that hMSCs can be utilized as a cell resource for tissue engineering and as human models to study cell differentiation mechanisms, such as adipogenesis, osteoblastogenesis and so on. Since it takes 2-3weeks for hMSCs to differentiate into adipocytes using conventional culture methods, the development of methods to induce faster differentiation into adipocytes is required. In this study we optimized the culture conditions for adipocyte induction to achieve a shorter cultivation time for the induction of adipocyte differentiation in bone marrow-derived hMSCs. Briefly, we used a cocktail of dexamethasone, insulin, methylisobutylxanthine (DIM) plus a peroxisome proliferator-activated receptor gamma agonist, rosiglitazone (DIMRo) as a new adipogenic differentiation medium. We successfully shortened the period of cultivation to 7-8days from 2-3weeks. We also found that rosiglitazone alone was unable to induce adipocyte differentiation from hMSCs in vitro. However, rosiglitazone appears to enhance hMSC adipogenesis in the presence of other hormones and/or compounds, such as DIM. Furthermore, the inhibitory activity of TGF-beta1 on adipogenesis could be investigated using DIMRo-treated hMSCs. We conclude that our rapid new culture method is very useful in measuring the effect of molecules that affect adipogenesis in hMSCs.

High expression level of Toll-like receptor 2 on monocytes is an important risk factor for arteriosclerotic disease.

BACKGROUND: Toll-like receptors (TLRs) recognize pathogen-associated molecular patterns to initiate an innate immune response. We previously reported upregulation of TLR2 expression level on monocytes of stable angina pectoris patients with significant coronary artery disease (CAD) relative to control patients without significant CAD. In this study we aimed to determine whether high level of Toll-like receptor 2 (TLR2) is a risk factor for atherogenesis, independent of established risk factors including smoking, diabetes mellitus (DM), hypertension (HT), and hyperlipidemia (HL). METHODS: TLR2 expression level on circulating monocyte surfaces was measured by using our developed flow cytometry assay. Patients were classified into two groups: "Arteriosclerotic disease" group (n=108) and "Control" group (n=70). Patients of the first group had arteriosclerotic disease such as CAD, aortic aneurysm, or peripheral arterial disease (PAD). The "Control" group was sex- and age-matched to the "Arteriosclerotic disease" group. RESULTS: TLR2 expression was significantly higher in the "Arteriosclerotic disease" group than in the "Control" group (p<0.001). Multivariate ordinal logistic regression analysis was performed; other known risk factors, which were represented to two nominal score points, 0 or 1, for patients with and without it, respectively, and TLR2 level, which was treated as a metric variable. DM (p=0.002), HT (p=0.001), HL (p<0.001), and TLR2 level (p<0.001) were identified as significant contributors for arteriosclerotic disease. CONCLUSIONS: High TLR2 expression level on monocytes may be an independent risk factor for atherogenesis.

Usefulness of the adenosine triphosphate with a sufficient observation period for detecting reconduction after pulmonary vein isolation.

BACKGROUND: Although reconduction after pulmonary vein (PV) isolation is considered to play a key role in the recurrence of paroxysmal atrial fibrillation (AF), there have been few reports regarding the precise time course of early reconduction. Several studies have suggested that transient PV reconduction facilitated by adenosine may predict long-term AF recurrence. This study was designed to clarify the incidence and time course of early reconduction after PVI during the procedure and to confirm whether the use of ATP after a certain observation period was useful to detect early reconduction after PVI. METHODS: In 21 patients (18 males, 56 +/- 11 years) with drug refractory AF, radiofrequency circumferential PV antrum ablation was performed in all 4 PVs. After the completion of isolation, electrograms in each PV were repeatedly recorded (1.98 +/- 0.57 times per PV) using a circular mapping catheter for an observation period of 87 +/- 29 minutes. After isolation of all 4 PVs, 30 mg of adenosine triphosphate (ATP) was administered during isoproterenol infusion. RESULTS: PV electrical isolation was initially achieved in all 81 PVs. During the observation period, 12 (15%) PVs in 10 (48%) of 21 patients exhibited spontaneous reconduction. Among the remaining 69 PVs, 8 (12%) additional PVs had reconduction with the use of ATP. All PV reconduction was successfully eliminated by 4.5 +/- 2.2 additional radiofrequency applications. CONCLUSION: A sufficient observation period and the use of ATP are useful to detect early reconduction after PV isolation.

The role of infection in the development of non-valvular atrial fibrillation: up-regulation of Toll-like receptor 2 expression levels on monocytes.

Many studies have suggested that inflammation may participate in the pathogenesis of non-valvular atrial fibrillation (AF). However, it has been unknown by exposure to what the inflammation is caused. Recently, we reported that Toll-like receptor 2 (TLR2) level on monocytes was significantly up-regulated in viral and bacterial infections, but not in non-infectious inflammatory states. Our purpose was to test the hypothesis that expression of TLR2 levels may be up-regulated in patients with non-valvular AF. A total of 48 consecutive patients with non-valvular AF who were hospitalized for catheter ablation were enrolled in this study. TLR2 levels were assayed by using flow-cytometric analysis and compared with volunteers in sinus rhythm (control group, n = 24). Additionally, C-reactive protein (CRP) and interleukin-6 (IL-6) levels were assayed, and the left atrial volume indexes (LAVI) in the non-valvular AF group were measured. The results demonstrated that TLR2 levels in the non-valvular AF group were significantly higher than in the control group (median, 4682 vs. 3866 sites/cell; P < 0.01). Moreover, non-valvular AF patients had significantly higher IL-6 levels than controls. However, there was no significant difference in CRP levels between the two groups. It was observed in 44 AF patients, in whom pulmonary vein isolation was confirmed to be successful, that the LAVI significantly diminished 1 month after ablation (median, 33.6 vs. 29.5 ml/m²; P < 0.001), but not the TLR2 and IL-6 levels. Our results implied that an infectious inflammation may participate in the pathogenesis of non-valvular AF.

A technique for diagnosis of accessory pathway using the H-H and A-A intervals of the first entrained cycle during ventricular overdrive pacing.

Although advancement of succeeding atrial activation by a ventricular extrastimulus (VES) on His refractoriness during supraventricular tachycardia (SVT) has been used as evidence of an accessory pathway (AP), the sensitivity of this method is suboptimal. This study was designed to compare the His-His (H-H) and atrial-atrial (A-A) intervals of the first entrained cycle during ventricular overdrive pacing (VOD) for the diagnosis of AP, in comparison to the conventional VES method. In 55 patients with SVT, a VES was elicited on His refractoriness during SVT. VOD was subsequently performed at cycle lengths 30 to 40 ms shorter than SVT cycle lengths. When the A-A interval became equal to the pacing cycle length after some beats of VOD, the cycle was considered the first entrained cycle and the H-H interval preceding the A-A interval was measured. VES advanced the next atrial activation in 16 patients (52%) with an AP, but in no patient without an AP. The H-H interval of the first entrained cycle was longer than the pacing cycle length by > or =15 ms in all patients with an AP, but was equal to the pacing cycle length in all patients without an AP. The criterion of H-H greater than A-A by > or =15 ms for the first entrained cycle provided higher diagnostic yield for AP compared with the VES method(100% vs 52%, p <0.001). In conclusion, this new criterion reliably diagnoses the presence of an AP in patients with SVT, with higher sensitivity compared with the VES method.

Non-pulmonary vein epicardial foci of atrial fibrillation identified in the left atrium after pulmonary vein isolation.

BACKGROUND: Pulmonary vein (PV) isolation (PVI) has been demonstrated to be an effective technique for curing atrial fibrillation (AF). AF foci that cannot be isolated by PVI (non-PV foci) can become the cause of AF recurrence. The purpose of this study was to investigate the characteristics of non-PV AF foci. METHODS AND RESULTS: Two hundred consecutive patients with symptomatic AF underwent electrophysiologic studies. In all patients, successful ostial or antral PVI was achieved with a multielectrode basket catheter (MBC). In 45 patients, spontaneous AF was induced even after PVI. In 23 of those patients, 30 AF foci were found in the left atrium (LA) (12 in the PV antrum, and 18 in the LA wall). Twenty-six of those foci were eliminated by focal ablation guided by an MBC. Five of those foci (four in the PV antrum and one in the LA posterior wall) were speculated to be located epicardially because a small potential preceding the LA potential was recorded from the MBC electrodes during AF initiation at the successful ablation site where single large potentials were recorded during sinus rhythm and a longer duration of radiofrequency energy delivery was needed to eliminate them. CONCLUSIONS: MBC mapping with induction of spontaneous AF may be useful for identifying non-PV AF foci in the LA after PVI. In some of those non-PV foci, mainly around the PVI lesions, a few electrophysiologic findings suggesting an epicardial location were observed. This may be a rationale for the efficacy of extensive PV ablation.

Liver X receptor ligands inhibit the lipopolysaccharide-induced expression of microsomal prostaglandin E synthase-1 and diminish prostaglandin E2 production in murine peritoneal macrophages.

Microsomal prostaglandin E synthase (mPGES)-1, which is dramatically induced in macrophages by inflammatory stimuli such as lipopolysaccharide (LPS), catalyzes the conversion of cyclooxygenase-2 (COX-2) reaction product prostaglandin H(2) (PGH(2)) into prostaglandin E(2) (PGE(2)). The mPGES-1-derived PGE(2) is thought to help regulate inflammatory responses. On the other hand, excess PGE(2) derived from mPGES-1 contributes to the development of inflammatory diseases such as arthritis and inflammatory pain. Here, we examined the effects of liver X receptor (LXR) ligands on LPS-induced mPGES-1 expression in murine peritoneal macrophages. The LXR ligands 22(R)-hydroxycholesterol (22R-HC) and T0901317 reduced LPS-induced expression of mPGES-1 mRNA and mPGES-1 protein as well as that of COX-2 protein. However, LXR ligands did not influence the expression of microsomal PGES-2 (mPGES-2) or cytosolic PGES (cPGES) protein. Consequently, LXR ligands suppressed the production of PGE(2) in macrophages. These results suggest that LXR ligands diminish PGE(2) production by inhibiting the LPS-induced gene expression of the COX-2-mPGES-1 axis in LPS-activated macrophages.

Suppression of inducible nitric oxide synthase and cyclooxygenase-2 gene expression by 22(R)-hydroxycholesterol requires de novo protein synthesis in activated macrophages.

Liver X receptors (LXRs) play an important role in lipid metabolism. Recently, a role for these proteins was identified in suppressing the inflammatory response. However, it is not known whether the natural ligands of LXRs, e.g. 22(R)-hydroxycholesterol (22R-HC), can suppress the inflammatory response after the onset of inflammation. We demonstrate here that treatment of Lipopolysaccharide (LPS)-activated RAW264.7 macrophages with 22R-HC markedly suppressed nitric oxide (NO) production and inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) mRNA expression. Additionally, 22R-HC did not affect the DNA binding activity of NF-kappaB, AP-1 and C/EBP(s), important transcriptional factors for iNOS and COX-2 genes expression. Furthermore iNOS and COX-2 mRNA suppression by 22R-HC was diminished by cellular treatment with cycloheximide. These results suggest that 22R-HC suppresses the expression of iNOS and COX-2 genes through de novo protein synthesis of an unidentified protein in LPS-activated macrophages.

Polycomb group gene mel-18 modulates the self-renewal activity and cell cycle status of hematopoietic stem cells.

OBJECTIVE: Mel-18 is a member of the mammalian Polycomb group (PcG) genes. This family of genes regulates global gene expression in many biologic processes, including hematopoiesis and anterior-posterior axis formation by manipulating specific target genes, including members of the Hox family. Here, we demonstrate that mel-18 negatively regulates the self-renewal activity of hematopoietic stem cells (HSCs). MATERIALS AND METHODS: Long-term reconstitution activity was evaluated by competitive repopulating unit (CRU) and mean activity of the stem cells (MAS) assays in vivo in bone marrow cells (BMCs) derived from mel-18(-/-) and mel-18 tg mice. The expression levels of mel-18 and Hoxb4 were measured by quantitative real-time reverse transcription polymerase chain reaction. RESULTS: The Hoxb4 gene was highly expressed in HSCs derived from mel-18(-/-) mice. The observed CRUs were 3.21, 4.77, 3.32, and 1.64 CRU per 10(5) BMCs in mel-18(+/+), mel-18(-/-), C57BL/6, and mel-18 tg, respectively. MAS was 0.58, 0.18, 0.41, and 5.89 in mel-18(+/+), mel-18(-/-), C57BL/6, and mel-18 tg, respectively. The percentage in G0 phase HSCs (lin(-)flk2(-)c-Kit(+)Sca1+ cells) was increased in mel-18(-/-) mice and decreased in mel-18 tg mice. CONCLUSION: Loss or knockdown of mel-18 leads to the expression of Hoxb4, an increase in the proportion of HSCs in G0 phase, and the subsequent promotion of HSC self-renewal. These findings will enable us to develop new approaches for controlling HSC activity for hematopoietic transplantations based on ex vivo expansion of HSCs.

TCDD treatment eliminates the long-term reconstitution activity of hematopoietic stem cells.

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), an endocrine disrupting chemical (EDC), can cause carcinogenesis, immunosuppression, and teratogenesis, through a ligand-activated transcription factor, the aryl hydrocarbon receptor (AhR). Despite remarkable recent advances in stem cell biology, the influence of TCDD on hematopoietic stem cells (HSCs), which possess the ability to reconstitute long-term multilineage hematopoiesis, has not been well investigated. In this study we examined the influence of TCDD on HSCs enriched for CD34(-), c-kit(+), Sca-1(+), lineage negative (CD34-KSL) cells. The number of the CD34-KSL cells was found to be increased about four-fold upon a single oral administration of TCDD (40 micro g/kg body weight). Surprisingly, we found that these TCDD-treated cells almost lost long-term reconstitution activity. This defect was not present in AhR(-/-) mice. These findings suggest that modulation of AhR/ARNT system activity may have an effect on HSC function or survival.

Dimerization of the Polycomb-group protein Mel-18 is regulated by PKC phosphorylation.

The Polycomb-group (Pc-G) gene products form complexes via protein-protein interactions and maintain the transcriptional repression of genes involved in embryogenesis, cell cycle, and tumorigenesis. Previously, we have shown that mouse Mel-18, a Pc-G protein, has tumor suppressor gene-like activity and negatively regulates transcription. Here, we show in vitro by pull-down assays and in vivo in transiently transfected COS-7 cells that Mel-18 forms homodimers. Deletion analysis revealed that the N-terminal RING-finger and alpha-helix domains are required for homodimer formation. In addition, we demonstrated that Mel-18 homo-dimerization is regulated by protein kinase C (PKC) and protein phosphatases, such that dephosphorylated Mel-18 is able to homo-dimerize. These results suggest that the stoichiometry and/or equilibrium of subunits of the class II Polycomb complex containing Mel-18 might be regulated by changes in phosphorylation status via the PKC signaling pathway.