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Hsin-Chen Lee

Publications and source records attributed to Hsin-Chen Lee.

16 recordsLinked to original sources
PubMed2026

Mitochondrial translocation of DNMT3L suppresses oxidative phosphorylation and restrains megakaryopoiesis.

DNMT3L, a catalytically inactive member of the DNA methyltransferase family, is identified here as a negative regulator of megakaryopoiesis. In K562 cells undergoing PMA-induced megakaryocytic differentiation, DNMT3L protein levels declined progressively, and shRNA-mediated depletion enhanced differentiation, whereas overexpression attenuated it. Consistent with these findings, Dnmt3l-knockout mice exhibited elevated peripheral blood platelet counts and expanded bone marrow megakaryocytes. Mechanistically, megakaryocytic differentiation triggered rapid mitochondrial translocation of DNMT3L within 6 h; mitochondrial DNMT3L suppressed oxidative phosphorylation (OXPHOS) capacity and ATP production and downregulated mitochondrial-encoded genes spanning Complex I, III, IV, and ATP synthase, without altering mitochondrial DNA copy number. This metabolic suppression was mediated through compartment-specific remodeling of DNMT3L-containing protein complexes: upon differentiation, DNMT3L selectively dissociated from DNMT1 and DNMT3B in mitochondria, relieving the repressive constraint on OXPHOS, whereas in the nucleus DNMT3L remained associated with DNMT3A, which concomitantly accumulated during differentiation. These findings reveal a previously unrecognized mechanism by which a catalytically inactive epigenetic co-regulator spatially redistributes to coordinate mitochondrial metabolic output with nuclear epigenetic control, thereby facilitating terminal megakaryocytic maturation.

Animals↗
PubMed2006

Mitochondrial DNA mutations and mitochondrial DNA depletion in breast cancer.

Somatic mutations in mitochondrial DNA (mtDNA) have been demonstrated in various tumors, including breast cancer. However, it still remains unclear whether the alterations in mtDNA are related to the clinicopathological features and/or the prognosis in the breast cancer. We analyzed somatic mutations in the D-loop region, the common 4,977-bp deletion, and the copy number of mtDNA in breast cancer and paired nontumorous breast tissues from 60 Taiwanese patients. We found that 18 of the 60 (30%) breast cancers displayed somatic mutations in mtDNA D-loop region. The incidence of the 4,977-bp deletion in nontumorous breast tissues (47%) was much higher than that in breast cancers (5%). The copy number of mtDNA was significantly decreased in 38 of the 60 (63%) breast cancers as compared to their corresponding nontumorous breast tissues (P = 0.0008). The occurrence of D-loop mutations was associated with an older onset age (>or=50 years old, P = 0.042), and tumors that lacked expressions of estrogen receptor and progesterone receptor (P = 0.024). Patients with mtDNA D-loop mutation and breast cancer had significantly poorer disease-free survival than those without mutation, when assessed by Kaplan-Meier curves and log-rank test (P = 0.005). Multivariate Cox regression analysis indicated that a D-loop mutation is a significant marker that is independent of other clinical variables and that it can be used to assess the prognosis of patients. Our findings suggest that somatic mutations in mtDNA D-loop can be used as a new molecular prognostic indicator in breast cancer.

Age Factors↗
PubMed2006

Aberrant methylation of EDNRB and p16 genes in hepatocellular carcinoma (HCC) in Taiwan.

Epigenetic alternation via the promoter hypermethylation of putative tumor suppressor genes has been implicated in the development of hepatocellular carcinoma (HCC). In this study, we investigated the epigenetic changes in two candidate tumor suppressor genes, endothelin receptor type B (EDNRB) and p16, and their relation to the expression of these two genes in HCC. Methylation-specific polymerase chain reaction (MS-PCR) was performed to analyze the promoter methylation status of the EDNRB and p16 genes in tumors and paired non-tumor liver portions of 34 HCC patients. The mRNA expression was assessed by reverse transcription-PCR assay. Hypermethylation of the EDNRB and p16 genes was detected in 29.4% (10/34) and 32.3% (11/34) of HCC patients, respectively. Moreover, the reduction of mRNA expression was correlated to the promoter hypermethylation of the EDNRB and p16 genes. In conclusion, aberrant methylation of EDNRB and p16 genes is highly prevalent in HCC. It suggested that epigenetic alteration of the EDNRB and p16 genes may play an important role in the pathogenesis of HCC.

Carcinoma, Hepatocellular↗
PubMed2006

Anticancer effects of low-dose 10-hydroxycamptothecin in human colon cancer.

10-Hydroxycamptothecin (10-HCPT), an indole alkaloid isolated from a Chinese tree, Camptotheca acuminate, inhibits the activity of topoisomerase I and has a broad spectrum of anticancer activity in vitro and in vivo. However, its use has been limited due to its water-insolubility and toxicity with i.v. administration. The purpose of this study was to investigate the efficacy, toxicity and proper dosage of 10-HCPT as a single agent by oral administration in the treatment of human colon cancer. 10-HCPT significantly repressed the proliferation of Colo 205 cells at a relatively low concentration (5-20 nM). Flow cytometry analysis and western blot and apoptosis assays demonstrated that low-dose 10-HCPT arrested Colo 205 cells in the G2 phase of the cell cycle and triggered apoptosis through a caspase-3-dependent pathway. Moreover, following oral administration at doses of 2.5-7.5 mg/kg/2 days, significant suppression of tumor growth by 10-HCPT was observed in mouse xenografts. No acute toxicity was observed after an oral challenge of 10-HCPT in BALB/c-nude mice every 2 days. The results of this study suggest that a relatively low dose of 10-HCPT (p.o.) is able to inhibit the growth of colon cancer, facilitating the development of a new protocol of human trials with this anticancer drug.

Administration, Oral↗
PubMed2005

Accumulation of mitochondrial DNA with 4977-bp deletion in knee cartilage--an association with idiopathic osteoarthritis.

OBJECTIVE: Since mitochondrial DNA (mtDNA) mutations have been established to associate with the aging process and some degenerative diseases, we investigated the correlation between idiopathic osteoarthritis (OA) and the 4977-bp mtDNA deletion. DESIGN: Cartilage were collected from six sites in knee joints removed from 18 aged patients with idiopathic OA, 10 aged non-OA cadavers, 3 young cadavers (YC), and lateral femoral condyle of 9 young patients. Histopathologic changes were examined and the common 4977-bp mtDNA deletions were analyzed in young and elderly cartilages obtained from different sites in the knee joint. The association of the 4977-bp deletion of mtDNA with idiopathic OA and aging was evaluated. RESULTS: The 4977-bp mtDNA deletion was detected in 17 of the 18 OA patients, 9 of the 10 aged non-OA cadavers, and 1 of the 3 YC. None of the nine specimens collected from the lateral femoral condyle of young patients had a detectable deletion of mtDNA. The 4977-bp mtDNA deletion was not significantly correlated with the severity of OA graded by the Mankin score. The frequencies of occurrence of the 4977-bp mtDNA deletion were significantly different between the OA group and the aged non-OA control group (P=0.004) and between the aged non-OA group and the young control group (P=0.002). CONCLUSIONS: The results suggest that accumulation of the 4977-bp deletion of mtDNA in knee cartilage increases with age and may play a role in the development of idiopathic OA in the knee joint.

Adolescent↗
PubMed2005

Mitochondrial DNA mutations and mitochondrial DNA depletion in gastric cancer.

Gastric carcinoma is one of the most common types of cancer in Taiwan. Somatic mitochondrial DNA (mtDNA) alteration in gastric carcinoma and its association with clinicopathologic features remain unclear. When we used polymerase chain reaction (PCR) and direct sequencing, 15 of the 31 (48%) gastric carcinomas displayed somatic mutations in the D-loop region, a hot spot for mutations in mtDNA of human cancers. Ten (67%) cancers with the somatic mutations in the D-loop had insertion or deletion mutations in nucleotide position (np) 303-309 in the mononucleotide repeat region. One carcinoma carried tandem duplication and triplication flanked by mononucleotide repeats starting at np 311 and 568, respectively, in the D-loop. We also detected the common 4,977-bp deletion in 17 (55%) of the noncancerous tissue samples, but only in three (9%) carcinomas. Moreover, we quantified the mtDNA content using a competitive PCR technique and found that mtDNA depletion occurred in 17 (55%) of the gastric carcinomas. Although no significant association was found between clinicopathologic features and the mtDNA mutations in the D-loop, mtDNA depletion was observed significantly in the ulcerated, infiltrating (Borrmann's type III) and diffusely thick (Borrmann's type IV) types of gastric carcinomas (P = 0.018). Our results suggest that somatic mtDNA mutations and mtDNA depletion occur in gastric cancer and that mtDNA depletion is involved in carcinogenesis and/or cancer progression of gastric carcinoma.

Base Sequence↗
PubMed2005

Mitochondrial biogenesis and mitochondrial DNA maintenance of mammalian cells under oxidative stress.

Mitochondrial biogenesis and mitochondrial DNA (mtDNA) maintenance depend on coordinated expression of genes in the nucleus and mitochondria. A variety of intracellular and extracellular signals transmitted by hormones and second messengers have to be integrated to provide mammalian cells with a suitable abundance of mitochondria and mtDNA to meet their energy demand. It has been proposed that reactive oxygen species (ROS) and free radicals generated from respiratory chain are involved in the signaling from mitochondria to the nucleus. Increased oxidative stress may contribute to alterations in the abundance of mitochondria as well as the copy number and integrity of mtDNA in human cells in pathological conditions and in aging process. Within a certain level, ROS may induce stress responses by altering expression of specific nuclear genes to uphold the energy metabolism to rescue the cell. Once beyond the threshold, ROS may cause oxidative damage to mtDNA and other components of the affected cells and to elicit apoptosis by induction of mitochondrial membrane permeability transition and release of pro-apoptotic proteins such as cytochrome c. On the basis of recent findings gathered from this and other laboratories, we review the alterations in the abundance of mitochondria and mtDNA copy number of mammalian cells in response to oxidative stress and the signaling pathways that are involved.

Animals↗
PubMed2005

Mitochondrial genome instability and mtDNA depletion in human cancers.

An increase in the rate of glycolysis is one of the metabolic alterations in most cancer cells. However, the role of alterations in mitochondrial function and mitochondrial DNA (mtDNA) in carcinogenesis still remains unclear. In this study, we analyzed the nucleotide sequence of the D-loop and the copy number of mtDNA in 54 hepatocellular carcinomas (HCCs), 31 gastric, 31 lung, and 25 colorectal cancers as well as their corresponding non-tumorous tissues. The results revealed that 42.6% (23/54) of the HCCs, 51.6% (16/31) of the gastric cancers, 22.6% (7/31) of the lung cancers, and 40.0% (10/25) of the colorectal cancers harbored mutation(s) in the D-loop of mtDNA. The mtDNA mutations in 43.5% (10/23) of the HCCs, 62.5% (10/16) of the gastric cancers, 57.1% (4/7) of the lung cancers, and 90.0% (9/10) of the colorectal cancers were changes in the mononucleotide or dinucleotide repeats, deletions, or multiple insertions. Moreover, we found that there is a significant decrease in mtDNA copy number in 57.4% (31/54) of the HCCs, 54.8% (17/31) of the gastric cancers, 22.6% (7/31) of the lung cancers, and 28.0% (7/25) of the colorectal cancers compared with the corresponding non-tumorous tissues. It is noteworthy that the incidence of somatic mutations in the D-loop of mtDNA in the cancers of later stages was higher than that of the early-stage cancers. Taken together, our findings suggest that instability in the D-loop region of mtDNA, together with the decrease in mtDNA copy number, is involved in the carcinogenesis of human cancers.

DNA, Mitochondrial↗
PubMed2004

Polymorphisms of estrogen-metabolizing genes and risk of hepatocellular carcinoma in Taiwan females.

Estrogen has been related to the development of hepatocellular carcinoma (HCC). In this molecular epidemiological study, we used logistic regression to compare the genotype frequencies of estrogen-metabolizing genes that are involved in estrogen biogenesis (CYP17), hydroxylation (CYP1A1) and inactivation of the reactive metabolites (catechol-O-methyltransferase, COMT) in HCC patients and control subjects, and determined their relationship with the risk of female HCC. The heterozygous or homozygous variants of high activity CYP17 (A2), high inducibility CYP1A1(m1), and low activity COMT (L) alleles were considered as high-risk genotypes. We found that the risk of HCC was elevated in women harboring either heterozygous or homozygous variants of the CYP1A1 gene and the respective OR (and 95% confidence interval) were 6.61 (1.35, 32.43) and 12.00 (1.73, 83.46). Moreover, we found that the risk of HCC was increased in the female subjects harboring higher numbers of high-risk genotypes, but not in male subjects. The OR for female HCC associated with two putative high-risk genotypes was 12.63 (1.50, 106.37), and the OR for three putative high-risk genotypes was 16.67 (1.82, 152.77). These findings strongly suggest that estrogen play a critical role in female hepatocarcinogenesis.

Carcinoma, Hepatocellular↗
PubMed2004

Somatic mutations in the D-loop and decrease in the copy number of mitochondrial DNA in human hepatocellular carcinoma.

Somatic mutations in mitochondrial DNA (mtDNA) have been detected in many human cancers, including hepatocellular carcinoma (HCC). The D-loop region was found to be a "hot spot" for mutation in mtDNA of the tumors. However, effects of the D-loop mutations on the copy number of mtDNA in tumor tissues are poorly understood. Using direct sequencing, we examined mutations in the D-loop region of mtDNA in 61 HCCs and the corresponding non-tumor liver tissues. The results revealed that 39.3% of the HCCs carried somatic mutation(s) in the D-loop of mtDNA, and most of these mutations were homoplasmic. Moreover, 37.0% (10/27) of these mutations were T-to-C and G-to-A transitions and 40.7% (11/27) of them were located in the polycytidine stretch between nucleotide position (np) 303 and 309 of mtDNA. In addition, we found that mtDNA copy number of HCC was significantly decreased in 60.5% of the patients with hepatoma, especially in those with somatic mutation(s) in the D-loop of mtDNA (17/24). This decrease in mtDNA copy number was highly associated with the occurrence of point mutations near the replication origin of the heavy-strand of mtDNA. Interestingly, we found that 42.9% (6/14) of the HCCs without mutation in the D-loop had a reduced copy number of mtDNA, indicating that other unidentified factors involved in mitochondrial biogenesis might be defective in the tumor. The results obtained in this study strongly suggest that somatic mutations in the D-loop together with the decrease in the copy number of mtDNA may be an important event during the early phase of liver carcinogenesis.

Base Sequence↗
PubMed2003

Increased expression of manganese-superoxide dismutase in fibroblasts of patients with CPEO syndrome.

Alterations in the expression of free radical scavenging enzymes and production of reactive oxygen species (ROS) in tissue cells may contribute to the pathogenesis of mitochondrial diseases such as chronic progressive external ophthalmoplegia (CPEO) syndrome. Since the mitochondria with impaired respiratory function in affected tissues generate more ROS via electron leakage, we examined the expression levels of free radical scavenging enzymes in primary culture of muscle fibroblasts of eight patients with CPEO syndrome. The results showed that the enzyme activity and protein levels of Mn-SOD of the fibroblasts from CPEO patients were significantly increased but those of Cu,Zn-SOD, catalase and glutathione peroxidase (GPx) were not increased compared with controls. A similar pattern was observed in the mRNA levels of Mn-SOD and GPx in muscle fibroblasts of all CPEO patients. The activity ratios of Mn-SOD/catalase and Mn-SOD/GPx in muscle fibroblasts of the CPEO patients were increased 1.7-3.4 and 1.8- to 5.3-fold, respectively, compared to those of the controls. Moreover, by using flow cytometry we found that the production of O2(*-) and H2O2 in the fibroblasts was about 2 times higher than those of controls. The 8-OHdG/dG ratios in total DNA of muscle biopsies from three CPEO patients were much higher than those of age-matched controls as determined by high performance liquid chromatography (HPLC). In the light of these findings, we suggest that the increase in expression of Mn-SOD, ROS production and oxidative damage in affected tissues may play an important role in the pathogenesis and progression of the CPEO syndrome.

Autoradiography↗
PubMed2002

Increase in mitochondrial mass in human fibroblasts under oxidative stress and during replicative cell senescence.

Abnormal proliferation of mitochondria generally occurs in muscle of aged individuals and patients with mitochondrial myopathy. An increase in the mitochondrial DNA (mtDNA) copy number has also been observed in aging human tissues. However, the molecular mechanism underlying the increase in mitochondrial mass and mtDNA is still unclear. In a previous study, we demonstrated that sublethal levels of oxidative stress caused an increase in mitochondrial mass in human lung cells. In this communication, we report our recent findings that the mitochondrial mass in human lung fibroblasts (MRC-5) in a later proliferation stage is significantly increased compared to that in the early stages of proliferation. The extent of the increase in mitochondrial mass in the senescent cells was similar to that in cells in the early stages of proliferation that had been treated with low concentrations (< or = 180 microM) of hydrogen peroxide (H(2)O(2)). Moreover, we found that the rate of reactive oxygen species (ROS) production was higher in cells in the later proliferation stage compared to cells in the early proliferation stages. A similar phenomenon was also observed in cells in the early proliferation stages under low levels of oxidative stress. On the other hand, the mRNA levels of many nuclear DNA-encoded proteins involved in mitochondrial biogenesis, particularly nuclear respiratory factor-1, were found to increase in cells in later proliferation stages and in cells in early proliferation stages that had been treated with 180 microM H(2)O(2). Interestingly, the increase in mitochondrial mass in the cells under oxidative stress could be repressed by treatment with cycloheximide or m-chlorocarbonyl cyanide phenylhydrazone but not by chloramphenicol. Furthermore, the mitochondrial mass of mtDNA-less rho(o) cells was also significantly increased by exposure to low concentrations (e.g. 180 microM) of H(2)O(2). These results suggest that the increase in mitochondrial mass in replicative senescent cells may result from an increase in ROS production, and that it is dependent on both de novo synthesis of nuclear DNA-encoded proteins and their import into mitochondria, dictated by the membrane potential of mitochondria.

Cells, Cultured↗
PubMed2002

Oxidative stress, mitochondrial DNA mutation, and impairment of antioxidant enzymes in aging.

Mitochondria do not only produce less ATP, but they also increase the production of reactive oxygen species (ROS) as by-products of aerobic metabolism in the aging tissues of the human and animals. It is now generally accepted that aging-associated respiratory function decline can result in enhanced production of ROS in mitochondria. Moreover, the activities of free radical-scavenging enzymes are altered in the aging process. The concurrent age-related changes of these two systems result in the elevation of oxidative stress in aging tissues. Within a certain concentration range, ROS may induce stress response of the cells by altering expression of respiratory genes to uphold the energy metabolism to rescue the cell. However, beyond the threshold, ROS may cause a wide spectrum of oxidative damage to various cellular components to result in cell death or elicit apoptosis by induction of mitochondrial membrane permeability transition and release of apoptogenic factors such as cytochrome c. Moreover, oxidative damage and large-scale deletion and duplication of mitochondrial DNA (mtDNA) have been found to increase with age in various tissues of the human. Mitochondria act like a biosensor of oxidative stress and they enable cell to undergo changes in aging and age-related diseases. On the other hand, it has recently been demonstrated that impairment in mitochondrial respiration and oxidative phosphorylation elicits an increase in oxidative stress and causes a host of mtDNA rearrangements and deletions. Here, we review work done in the past few years to support our view that oxidative stress and oxidative damage are a result of concurrent accumulation of mtDNA mutations and defective antioxidant enzymes in human aging.

Aging↗
PubMedDate not supplied

Mitochondrial DNA mutations in light-associated skin tumors.

Mutations of mitochondrial DNA (mtDNA) have been proposed to be involved in carcinogenesis. In this study, we applied the polymerase chain reaction techniques to investigate the frequency of occurrence and proportion of mtDNA with length mutations (deletions and tandem duplications) in light-associated skin tumors (actinic keratosis, AK; basal cell carcinoma, BCC; and squamous cell carcinoma, SCC) in aged individuals. We demonstrated the existence of multiple mtDNA deletions and tandem duplications in tissues of AK, BCC, SCC and normal skin. We showed that the frequencies of occurrence of the 4,977 bp and 7,436 bp deletions and tandem duplications (200 bp and 260 bp) of mtDNA in light-associated skin tumors were not significantly different from those of sun-exposed normal skin (p>0.05), but higher than those of non-exposed normal skin (p<0.05). In addition, we found that the proportion of the 4,977 bp-deleted mtDNA in the skin of the same individual was also affected by skin pathologies. The proportion of 4,977 bp-deleted mtDNA in relatively rapid growing tumor cells in SCC was lower than that of normal skin cells. We suggest that the existence of these length mutations of mtDNA in normal, precancerous or cancerous human skin may be attributed to the stochastic effect of photo-damage. However, it is unclear whether the mutations of mtDNA have a direct bearing on carcinogenesis in skin. Future investigation is warranted to elucidate the causal relationship between mtDNA mutations and skin cancers and to address the pathophysiological role of mtDNA mutations in skin cancer development.

Aged↗