[Show abstract][Hide abstract] ABSTRACT: Tissue repair in the adult mammalian liver occurs in two distinct processes, referred to as the first and second tiers of defense. We undertook to characterize the changes in molecular constituents of the extracellular matrix when hepatic progenitor cells (HPCs) respond in a second tier of defense to liver injury.
We used transcriptional profiling on rat livers responding by a first tier (surgical removal of 70 % of the liver mass (PHx protocol)) and a second tier (70 % hepatectomy combined with exposure to 2-acetylaminofluorene (AAF/PHx protocol)) of defense to liver injury and compared the transcriptional signatures in untreated rat liver (control) with those from livers of day 1, day 5 and day 9 post hepatectomy in both protocols. Numerous transcripts encoding specific subunits of collagens, laminins, integrins, and various other extracellular matrix structural components were differentially up- or down-modulated (P < 0.01). The levels of a number of transcripts were significantly up-modulated, mainly in the second tier of defense (Agrn, Bgn, Fbn1, Col4a1, Col8a1, Col9a3, Lama5, Lamb1, Lamb2, Itga4, Igtb2, Itgb4, Itgb6, Nid2), and their signal intensities showed a strong or very strong correlation with Krt1-19, a well-established marker of a ductular/HPC reaction. Furthermore, a significant up-modulation and very strong correlation between the transcriptional profiles of Krt1-19 and St14 encoding matriptase, a component of a novel protease system, was found in the second tier of defense. Real-time PCR confirmed the modulation of St14 transcript levels and strong correlation to Krt-19 and also showed a significant up-modulation and strong correlation to Spint1 encoding HAI-1, a cognate inhibitor of matriptase. Immunodetection and three-dimensional reconstructions showed that laminin, Collagen1a1, agrin and nidogen1 surrounded bile ducts, proliferating cholangiocytes, and HPCs in ductular reactions regardless of the nature of defense. Similarly, matriptase and HAI-1 were expressed in cholangiocytes regardless of the tier of defense, but in the second tier of defense, a subpopulation of HPCs in ductular reactions co-expressed HAI-1 and the fetal hepatocyte marker Dlk1.
Transcriptional profiling and immunodetection, including three-dimensional reconstruction, generated a detailed overview of the extracellular matrix constituents expressed in a second tier of defense to liver injury.
[Show abstract][Hide abstract] ABSTRACT: Dynamic shifts in transcription factor binding are central to the regulation of biological processes by allowing rapid changes in gene transcription. However, very few genome-wide studies have examined how transcription factor occupancy is coordinated temporally in vivo in higher animals. Here, we quantified the genome-wide binding patterns of two key hepatocyte transcription factors, CEBPA and CEBPB (also known as C/EBPalpha and C/EBPbeta), at multiple time points during the highly dynamic process of liver regeneration elicited by partial hepatectomy in mouse. Combining these profiles with RNA polymerase II binding data, we find three temporal classes of transcription factor binding to be associated with distinct sets of regulated genes involved in the acute phase response, metabolic/homeostatic functions, or cell cycle progression. Moreover, we demonstrate a previously unrecognized early phase of homeostatic gene expression prior to S-phase entry. By analyzing the three classes of CEBP bound regions, we uncovered mutually exclusive sets of sequence motifs, suggesting temporal codes of CEBP recruitment by differential cobinding with other factors. These findings were validated by sequential ChIP experiments involving a panel of central transcription factors and/or by comparison to external ChIP-seq data. Our quantitative investigation not only provides in vivo evidence for the involvement of many new factors in liver regeneration but also points to similarities in the circuitries regulating self-renewal of differentiated cells. Taken together, our work emphasizes the power of global temporal analyses of transcription factor occupancy to elucidate mechanisms regulating dynamic biological processes in complex higher organisms.
[Show abstract][Hide abstract] ABSTRACT: TGFß signaling patterns the primitive streak, yet little is known about transcriptional effectors that mediate the cell fate choices during streak-like development in mammalian embryos and in embryonic stem (ES) cells. Here we demonstrate that cross-antagonistic actions of EVEN-SKIPPED HOMEOBOX 1 (EVX1) and GOOSECOID (GSC) regulate cell fate decisions in streak-like progenitors derived from human ES cells exposed to BMP4 and/or activin. We found that EVX1 repressed GSC expression and promoted formation of posterior streak-like progeny in response to BMP4, and conversely that GSC repressed EVX1 expression and was required for development of anterior streak-like progeny in response to activin. Chromatin immunoprecipitation assays showed that EVX1 bound to the GSC 5'-flanking region in BMP4 treated human ES cells, and band shift assays identified two EVX1 binding sites in the GSC 5'-region. Significantly, we found that intact EVX1 binding sites were required for BMP4-mediated repression of GSC reporter constructs. We conclude that BMP4-induced EVX1 repress GSC directly and the two genes form the core of a gene regulatory network (GRN) controlling cell fates in streak-like human ES cell progeny.
Full-text · Article · Dec 2011 · Developmental Biology
[Show abstract][Hide abstract] ABSTRACT: During liver development, intrahepatic bile ducts are thought to arise by a unique asymmetric mode of cholangiocyte tubulogenesis characterized by a series of remodeling stages. Moreover, in liver diseases, cells lining the Canals of Hering can proliferate and generate new hepatic tissue. The aim of this study was to develop protocols for three-dimensional visualization of protein expression, hepatic portal structures and human hepatic cholangiocyte tubulogenesis.
Protocols were developed to digitally visualize portal vessel branching and protein expression of hepatic cell lineage and extracellular matrix deposition markers in three dimensions. Samples from human prenatal livers ranging from 7 weeks + 2 days to 15½ weeks post conception as well as adult normal and acetaminophen intoxicated liver were used. The markers included cytokeratins (CK) 7 and 19, the epithelial cell adhesion molecule (EpCAM), hepatocyte paraffin 1 (HepPar1), sex determining region Y (SRY)-box 9 (SOX9), laminin, nestin, and aquaporin 1 (AQP1).Digital three-dimensional reconstructions using CK19 as a single marker protein disclosed a fine network of CK19 positive cells in the biliary tree in normal liver and in the extensive ductular reactions originating from intrahepatic bile ducts and branching into the parenchyma of the acetaminophen intoxicated liver. In the developing human liver, three-dimensional reconstructions using multiple marker proteins confirmed that the human intrahepatic biliary tree forms through several developmental stages involving an initial transition of primitive hepatocytes into cholangiocytes shaping the ductal plate followed by a process of maturation and remodeling where the intrahepatic biliary tree develops through an asymmetrical form of cholangiocyte tubulogenesis.
The developed protocols provide a novel and sophisticated three-dimensional visualization of vessels and protein expression in human liver during development and disease.
[Show abstract][Hide abstract] ABSTRACT: Compromised epithelial barriers are found in dysplastic tissue of the gastrointestinal tract. Claudins are transmembrane proteins important for tight junctions. Claudins regulate the paracellular transport and are crucial for maintaining a functional epithelial barrier. Down-regulation of the oncogenic serine protease, matriptase, induces leakiness in epithelial barriers both in vivo and in vitro. We found in an in-silico search tight co-regulation between matriptase and claudin-7 expression. We have previously shown that the matriptase expression level decreases during colorectal carcinogenesis. In the present study we investigated whether claudin-7 expression is likewise decreased during colorectal carcinogenesis, thereby causing or contributing to the compromised epithelial leakiness of dysplastic tissue.
The mRNA level of claudin-7 (CLDN7) was determined in samples from 18 healthy individuals, 100 individuals with dysplasia and 121 colorectal cancer patients using quantitative real time RT-PCR. In addition, immunohistochemical stainings were performed on colorectal adenomas and carcinomas, to confirm the mRNA findings.
A 2.7-fold reduction in the claudin-7 mRNA level was found when comparing the biopsies from healthy individuals with the biopsies of carcinomas (p < 0.001). Reductions in the claudin-7 mRNA levels were also detected in mild/moderate dysplasia (p < 0.001), severe dysplasia (p < 0.01) and carcinomas (p < 0.01), compared to a control sample from the same individual. The decrease at mRNA level was confirmed at the protein level by immunohistochemical stainings.
Our results show that the claudin-7 mRNA level is decreased already as an early event in colorectal carcinogenesis, probably contributing to the compromised epithelial barrier in adenomas.
[Show abstract][Hide abstract] ABSTRACT: Cerebral edema is a feared complication to acute liver failure (ALF), but the pathogenesis is still poorly understood. The water channels Aquaporin-1 (Aqp1) and -4 (Aqp4) has been associated with brain edema formation in several neuropathological conditions, indicating a possible role of Aqp1 and/or Aqp4 in ALF mediated brain edema. We induced acute liver injury and hyperammonemia in mice, to evaluate brain edema formation and the parallel expression of Aqp1 and Aqp4 in ALF. Liver injury and hyperammonemia were induced by +D-galactosamine (GLN) plus lipopolysaccharide (LPS) intraperitoneally and intravenous ammonia-acetate (NH(4)(+)), the GLN+LPS+NH(4)(+) group. The vehicle control group (CONTROL) was treated with NaCl and phosphate-buffered saline. The GLN+LPS+NH(4)(+) group showed significantly elevated p-alanine aminotransferase, p-INR and p-ammonium vs. CONTROL (p < 0.001). Cortical brain water content was significantly elevated in the GLN+LPS+NH(4)(+) group vs. CONTROL, mean (SEM) 80.8(0.3) vs 80.0(0.1) % (p < 0.05). Western blot of membrane enriched cortical brain tissue showed significantly upregulation of Aqp4 in the GLN+LPS+NH(4)(+) group vs. CONTROL, mean AU (SEM) 100775(14820) vs. 58857(6266) (p < 0.05), and stationary levels for Aqp1. Aqp1 and Aqp4 mRNA were stationary. This study indicates that Aqp4, but not Aqp1, may be of importance in the pathogenesis of cortical brain edema in mice with ALF.
No preview · Article · Oct 2010 · Metabolic Brain Disease
[Show abstract][Hide abstract] ABSTRACT: Nonsense-mediated mRNA decay (NMD) is a post-transcriptional RNA surveillance process that facilitates the recognition and destruction of mRNAs bearing premature terminations codons (PTCs). Such PTC-containing (PTC+) mRNAs may arise from different processes, including erroneous processing and expression of pseudogenes, but also from more regulated events such as alternative splicing coupled NMD (AS-NMD). Thus, the NMD pathway serves both as a silencer of genomic noise and a regulator of gene expression. Given the early embryonic lethality in NMD deficient mice, uncovering the full regulatory potential of the NMD pathway in mammals will require the functional assessment of NMD in different tissues.
Here we use mouse genetics to address the role of UPF2, a core NMD component, in the development, function and regeneration of the liver. We find that loss of NMD during fetal liver development is incompatible with postnatal life due to failure of terminal differentiation. Moreover, deletion of Upf2 in the adult liver results in hepatosteatosis and disruption of liver homeostasis. Finally, NMD was found to be absolutely required for liver regeneration.
Collectively, our data demonstrate the critical role of the NMD pathway in liver development, function and regeneration and highlights the importance of NMD for mammalian biology.
[Show abstract][Hide abstract] ABSTRACT: Clinical trials where cancer patients were treated with protease inhibitors have suggested that the serine protease, prostasin, may act as a tumour suppressor. Prostasin is proteolytically activated by the serine protease, matriptase, which has a very high oncogenic potential. Prostasin is inhibited by protease nexin-1 (PN-1) and the two isoforms encoded by the mRNA splice variants of hepatocyte growth factor activator inhibitor-1 (HAI-1), HAI-1A, and HAI-1B.
Using quantitative RT-PCR, we have determined the mRNA levels for prostasin and PN-1 in colorectal cancer tissue (n = 116), severe dysplasia (n = 13), mild/moderate dysplasia (n = 93), and in normal tissue from the same individuals. In addition, corresponding tissues were examined from healthy volunteers (n = 23). A part of the cohort was further analysed for the mRNA levels of the two variants of HAI-1, here denoted HAI-1A and HAI-1B. mRNA levels were normalised to beta-actin. Immunohistochemical analysis of prostasin and HAI-1 was performed on normal and cancer tissue.
The mRNA level of prostasin was slightly but significantly decreased in both mild/moderate dysplasia (p < 0.001) and severe dysplasia (p < 0.01) and in carcinomas (p < 0.05) compared to normal tissue from the same individual. The mRNA level of PN-1 was more that two-fold elevated in colorectal cancer tissue as compared to healthy individuals (p < 0.001) and elevated in both mild/moderate dysplasia (p < 0.01), severe dysplasia (p < 0.05) and in colorectal cancer tissue (p < 0.001) as compared to normal tissue from the same individual. The mRNA levels of HAI-1A and HAI-1B mRNAs showed the same patterns of expression. Immunohistochemistry showed that prostasin is located mainly on the apical plasma membrane in normal colorectal tissue. A large variation was found in the degree of polarization of prostasin in colorectal cancer tissue.
These results show that the mRNA level of PN-1 is significantly elevated in colorectal cancer tissue. Future studies are required to clarify whether down-regulation of prostasin activity via up regulation of PN-1 is causing the malignant progression or if it is a consequence of it.
[Show abstract][Hide abstract] ABSTRACT: Barrett's esophagus (BE) represents a major risk factor for esophageal adenocarcinoma (AC). For this reason, patients with BE are subjected to a systematic endoscopic surveillance to detect initial evolution towards non-invasive neoplasia (NiN) and cancer, that eventually occurs only in a small fraction of BE patients. This study was aimed to investigate the possible role of glutathione-S-transferase-omega 1 (GSTO1), a recently discovered member of the glutathione-S-transferase family, as a progression marker in the Barrett's disease in order to improve the diagnosis of NiN in BE and to understand the mechanisms of the progression from BE to AC. We investigated the expression and subcellular localization of GSTO1 in biopsies from patients with BE and in human cancer cell lines subjected to heath shock treatment. A selective nuclear localisation of GSTO1 was found in 16/16 biopsies with low- or high-grade NiN, while it appeared in only 4/22 BE biopsies without signs of NiN (P<0.0001). Among biopsies of BE without NiN, diffuse (nuclear and cytoplasmic) staining was found in 5/22 cases, while selective cytoplasmic localisation was found in 13/22. The 6 cases with indefinite grade of NiN were equally divided between nuclear, cytoplasmic and diffuse staining (2 each, respectively). Experiments in vitro showed that in human HeLa cancer cells, GSTO1 translocates into the nucleus as a consequence of heath shock. These findings suggested that the nuclear translocation of glutathione-S-transferase-omega 1 could be involved in the stress response of human cells playing a role in the cancer progression of Barrett's esophagus. Its immunohistochemical detection could represent a useful tool in the grading of Barrett's disease.
[Show abstract][Hide abstract] ABSTRACT: Delta-like protein (DLK) is a membrane protein with mostly unknown function. It is expressed by several embryonic tissues among others by the hepatoblasts of rodent and human fetal livers. We have investigated in the present study if this protein is expressed in human hepatoblastomas. The presence of DLK has been studied by standard immunohistochemistry in 31 hepatoblastomas and in several differential diagnostically related tumours: hepatocellular carcinomas and in undifferentiated childhood neoplasms. All the hepatoblastomas were positive for DLK; the surrounding liver tissue remained negative. The reaction was present in the epithelial component of the tumours. The staining pattern was mostly membranous, occasionally cytoplasmic. The other studied tumours were negative for DLK, except one hepatocellular carcinoma and the differentiating cells of two ganglioneuroblastomas. Therefore, DLK seems to be a highly sensitive and specific marker for hepatoblastomas.
Full-text · Article · May 2008 · Archiv für Pathologische Anatomie und Physiologie und für Klinische Medicin
[Show abstract][Hide abstract] ABSTRACT: Thy-1, a marker of hematopoietic stem cells, has been reported to be expressed by oval cells proliferating during stem cell-mediated regeneration in rat liver, suggesting a relationship between the two cell populations. Consequently, Thy-1 has become an accepted cell surface marker to sort hepatic oval cells. In the present study we used the well-characterized 2-acetylaminfluorene/partial hepatectomy model to induce transit-amplification of hepatic oval cells in the regenerating liver and characterized Thy-1 expression using Northern hybridization, quantitative reverse transcriptase-polymerase chain reaction analysis, immunofluorescence confocal microscopy, and immunoelectronmicroscopy. We found that Thy-1 expression was induced during transit-amplification of the oval cell population, but Thy-1 mRNA was not present in the alpha-fetoprotein-expressing oval cells. Thy-1 protein was consistently present outside the basement membrane surrounding the oval cells. It overlapped frequently with smooth muscle actin staining. A similar cellular localization of the Thy-1 protein was found on human liver specimens with ductular reactions obtained from patients with fulminant liver failure. Furthermore, Thy-1 was expressed by myofibroblasts in experimental liver fibrosis models without oval cell proliferation. We conclude that Thy-1 is not a marker of oval cells but is present on a subpopulation of myofibroblasts/stellate cells.
Full-text · Article · Dec 2007 · American Journal Of Pathology
[Show abstract][Hide abstract] ABSTRACT: The experimental protocols used in the investigation of stem cell-mediated liver regeneration in rodents are characterized by activation of the hepatic stem cell compartment in the canals of Hering followed by transit amplification of oval cells and their subsequent differentiation along hepatic lineages. Although the protocols are numerous and often used interchangeably across species, a thorough comparative phenotypic analysis of oval cells in rats and mice using well-established and generally acknowledged molecular markers has not been provided. In the present study, we evaluated and compared the molecular phenotypes of oval cells in several of the most commonly used protocols of stem cell-mediated liver regeneration-namely, treatment with 2-acetylaminofluorene and partial (70%) hepatectomy (AAF/PHx); a choline-deficient, ethionine-supplemented (CDE) diet; a 3,5-diethoxycarbonyl-1,4-dihydro-collidin (DDC) diet; and N-acetyl-paraaminophen (APAP). Reproducibly, oval cells showing reactivity for cytokeratins (CKs), muscle pyruvate kinase (MPK), the adenosine triphosphate-binding cassette transporter ABCG2/BCRP1 (ABCG2), alpha-fetoprotein (AFP), and delta-like protein 1/preadipocyte factor 1 (Dlk/Pref-1) were induced in rat liver treated according to the AAF/PHx and CDE but not the DDC protocol. In mouse liver, the CDE, DDC, and APAP protocols all induced CKs and ABCG2-positive oval cells. However, AFP and Dlk/Pref-1 expression was rarely detected in oval cells. CONCLUSION: Our results delineate remarkable phenotypic discrepancies exhibited by oval cells in stem cell-mediated liver regeneration between rats and mice and underline the importance of careful extrapolation between individual species.
[Show abstract][Hide abstract] ABSTRACT: Trefoil factors (TFFs) 1, 2, and 3 are expressed in mucosal epithelia. TFFs are particular abundant in the intestine in which they play a crucial role in maintenance and restitution of the epithelium. Because pancreas developmentally arises from the primitive foregut, we explored the expression of TFFs in the pancreas in man and rat. Immunocytochemical staining of adult human pancreas showed abundant TFF3 immunoreactivity in pancreatic islets and some duct cells, whereas weak TFF1 and no TFF2 staining were detected. In the islets TFF3 localized to most insulin and some glucagon and pancreatic polypeptide-producing cells. TFF3 immunoreactivity was colocalized with insulin and glucagon in distinct cell clusters in human fetal pancreas at wk 14 and in the newborn rat pancreas. In isolated human and rat islets, TFF3 and TFF1 mRNA was identified by RT-PCR, and TFF3 protein was detected in human pancreas and islets by ELISA. Exposure of neonatal rat islets or insulinoma cells to GH, a known beta-cell growth factor, resulted in markedly increased TFF3 but decreased TFF1 mRNA levels. The effect of GH on TFF3 expression was confirmed by Western blot. Culture of neonatal rat islets in the presence of TFF3 resulted in attachment and migration of the islet cells, but no effects on proliferation, insulin secretion or cytokine-induced apoptosis were seen. These data demonstrate expression of TFFs in the endocrine pancreas, but their possible functions remain unknown.
[Show abstract][Hide abstract] ABSTRACT: Although normally quiescent, the adult mammalian liver possesses a great capacity to regenerate after different types of injuries in order to restore the lost liver mass and ensure maintenance of the multiple liver functions. Major players in the regeneration process are mature residual cells, including hepatocytes, cholangiocytes and stromal cells. However, if the regenerative capacity of mature cells is impaired by liver-damaging agents, hepatic progenitor cells are activated and expand into the liver parenchyma. Upon transit amplification, the progenitor cells may generate new hepatocytes and biliary cells to restore liver homeostasis. In recent years, hepatic progenitor cells have been the subject of increasing interest due to their therapeutic potential in numerous liver diseases as alternative or supportive/complementary tools to liver transplantation. While the first investigations on hepatic progenitor cells have focused on their origin and phenotypic characterization, recent attention has focused on the influence of the hepatic microenvironment on their activation and proliferation. This microenvironment comprises the extracellular matrix, epithelial and non-epithelial resident liver cells, and recruited inflammatory cells as well as the variety of growth-modulating molecules produced and/or harboured by these elements. The cellular and molecular responses to different regenerative stimuli seem to depend on the injury inflicted and consequently on the molecular microenvironment created in the liver by a certain insult. This review will focus on molecular responses controlling activation and expansion of the hepatic progenitor cell niche, emphasizing similarities and differences in the microenvironments orchestrating regeneration by recruitment of progenitor cell populations or by replication of mature cells.
[Show abstract][Hide abstract] ABSTRACT: The polychaete Capitella capitata sp.I has a high capacity to metabolize polycyclic aromatic hydrocarbons (PAHs) which are among the most hazardous environmental pollutants with significant biological effects. In the present study, two novel cytochrome P450 (CYP) genes were identified in this species. One was named CYP331A1, the first member of a new family of CYP331, and the other CYP4AT1 is the first member of a new subfamily CYP4AT. Both of these genes are constitutively expressed in the worms and detectable by RT-PCR. The expression of CYP331A1 mRNA was observed to be more sensitive to PAH exposure than CYP4AT1, which indicated that CYP331A1 should play a more important role than CYP4AT1 in PAH metabolism in this species. Considering the importance of C. capitata sp.I in taking up PAH and other organic pollutants from contaminated marine sediments with the potential for subsequent food-chain transfer, our results are important for understanding the molecular basis of biotransformation and detoxification in this invertebrate, and also have evolutionary significance for understanding the diversity and history of the CYP superfamily.
No preview · Article · Jan 2005 · Biochemical and Biophysical Research Communications
[Show abstract][Hide abstract] ABSTRACT: Hepatic regeneration from toxic or surgical injury to the adult mammalian liver, endorses different cellular responses within the hepatic lineage. The molecular mechanisms determining commitment of a cell population at a specific lineage level to participate in liver repair as well as the fate of its progeny in the hostile environment created by the injury are not well defined. Based on the role of the Notch/Delta/Jagged system in cell fate specification and recent reports linking Notch signaling with normal bile duct formation in mouse and human liver, we examined the expression of Notch1, Notch2, Notch3, Delta1, Delta3, Jagged1, and Jagged2, and delta-like protein/preadipocyte factor 1/fetal antigen 1 (dlk) in four well-defined experimental rat models of liver injury and regeneration. Although Delta3 and Jagged2 were undetectable by reverse transcriptase-polymerase chain reaction and Northern blot, we observed the most significant up-regulation of all other transcripts in the 2-acetylaminofluorene-70% hepatectomy (AAF/PHx) model, in which liver mass is restored by proliferation and differentiation of transit-amplifying ductular (oval) cells. The most profound change was observed for dlk. Accordingly, immunohistochemical analyses in the AAF/PHx model showed a specific expression of dlk in atypical ductular structures composed of oval cells. Delta-like protein was not observed in proliferating hepatocytes or bile duct cells after partial hepatectomy or ligation of the common bile duct whereas clusters of dlk immunoreactive oval cells were found in both the retrorsine and the AAF/PHx models. Finally, we used dlk to isolate alpha-fetoprotein-positive cells from fetal and adult regenerating rat liver by a novel antibody panning technique.
Full-text · Article · May 2004 · American Journal Of Pathology
[Show abstract][Hide abstract] ABSTRACT: We have evaluated cell survival, apoptosis, and cell cycle responses in a panel of DNA mismatch repair (MMR)-deficient colon and prostate cancer cell lines after alkylation and UV-C damage. We show that although these MMR-deficient cells tolerate alkylation damage, they are as sensitive to UV-C-induced damage as are the MMR-proficient cells. MMR-proficient cells arrest in the S-G2 phase of the cell cycle and initiate apoptosis following alkylation damage, whereas MMR-deficient cells continue proliferation. However, two prostate cancer cell lines that are MMR-deficient surprisingly arrest transiently in S-G2 after alkylation damage. Progression through G1 phase initially depends on the expression of one or more of the D-type cyclins (D1, D2, and/or D3). Analysis of cyclin D1 expression shows an initial MMR-independent decrease in the protein level after alkylation as well as UV-C damage. At later time points, however, only DNA damage-arrested cells showed decreased cyclin D1 levels irrespective of MMR status, indicating that reduced cyclin D1 could be a result of a smaller fraction of cells being in G1 phase rather than a result of an intact MMR system. Finally, we show that cyclin D1 is degraded by the proteasome in response to alkylation damage.
No preview · Article · Feb 2004 · Experimental Cell Research