The ets sequence from the transforming gene of avian erythroblastosis virus, E26, has unique domains on human chromosomes 11 and 21: both loci are transcriptionally active.

Human DNA segments homologous to the ets region from the transforming gene of avian erythroblastosis virus, E26, were molecularly cloned and shown to be closely related to the viral equivalent by hybridization and partial sequence analysis. The transforming gene of E26 has a tripartite origin with the structure delta gag [1.2 kilobases (kb) from the viral gag gene]-myb(0.9 kb from the chicken myb gene)-ets (1.6 kb from the chicken ets gene). Human ets DNA is located on two distinct human chromosomes. The human ets-1 locus on chromosome 11 encodes a single mRNA of 6.8 kb; the second locus, ets-2 on chromosome 21, encodes three mRNAs of 4.7, 3.2, and 2.7 kb. The ets-related sequences of human DNA on chromosomes 11 and 21 are discontiguous, except for a small overlap region encoding 14 amino acids, where 12 are conserved between these two loci. By contrast, the chicken homolog has contiguous ets-1 and ets-2 sequences and is primarily expressed in normal chicken cells as a single 7.5-kb mRNA. We conclude that the ets sequence shared by the virus, the chicken, and humans is likely to contain at least two dissociable functional domains, ets-1 and ets-2. Thus, the tripartite transforming gene of E26 includes four distinct domains that may be functionally relevant for the transforming function of the virus (delta gag, myb, ets-1, and ets-2).     

Cloning and expression profile of FLT3 gene during progenitor cell-dependent liver regeneration

BACKGROUND AND AIM: The liver has a unique capacity to regenerate upon exposure to viral infections, toxic reactions and cancer formation. Liver regeneration is a complex phenomenon in which several factors participate during its onset. Cellular proliferation is an important component of this process and the factors that regulate this proliferation have a vital role. FLT3, a well-known hematopoietic stem cell and hepatic lineage surface marker, is involved in proliferative events of hematopoietic stem cells. However, its contribution to liver regeneration is not known. Therefore, the aim of this study was to clone and examine the role of FLT3 during liver regeneration in rats. METHODS: Partial cDNA of rat homolog of FLT3 gene was cloned from thymus and the tissue specific expression of this gene at mRNA and protein levels was examined by RT-PCR and Western blot. After treating with 2-AAF and performing hepatectomy in rats to induce progenitor-dependent liver regeneration, the mRNA and protein expression profile of FLT3 was investigated by real-time PCR and Western blot during liver regeneration. In addition, cellular localization of FLT3 protein was determined by immunohistochemistry. RESULTS: The results indicated that rat FLT3 cDNA has high homology with mouse and human FLT3 cDNA. It was also found that FLT3 is expressed in most of the rat tissues and during liver regeneration. In addition, its intracellular localization is altered during the late stages of liver regeneration. CONCLUSION: The FLT3 receptor is activated at the late stages of liver regeneration and participates in the proliferation response that is observed during progenitor-dependent liver regeneration.     

Locus unlinked to alpha-fetoprotein under the control of the murine raf and Rif genes.

The levels of alpha-fetoprotein mRNA in mice are determined by at least two trans-acting, unlinked genes, raf and Rif. raf determines the basal levels of alpha-fetoprotein mRNA in adult mice, while Rif determines its degree of inducibility during liver regeneration. To determine whether these regulatory loci affect other structural genes, we screened a murine fetal liver cDNA library for clones containing mRNA sequences that decrease after birth. One such clone, termed pH19, was identified, and its mRNA was shown to be under the control of both raf and Rif. The single-copy gene for H19 mRNA was localized to chromosome 7, and genetic crosses established that it was unlinked to either raf or Rif. It encodes a 2.5-kilobase mRNA that was identified in those tissues that produce alpha-fetoprotein: visceral endoderm, liver, and fetal gut. The repression of H19 mRNA in neonatal liver occurs several days after the decrease in alpha-fetoprotein mRNA, whereas inductions of both mRNAs during the differentiation of F9 teratocarcinoma cells into visceral endoderm were identical. The tissue-specific expression of H19 mRNA is different from that of alpha-fetoprotein in that H19 mRNA was detected also in both cardiac and skeletal muscle where no alpha-fetoprotein mRNA is produced. Despite the fact that the levels of H19 mRNA decline to 1/10th to 1/20th in cardiac muscle after birth, the adult basal levels are not under the influence of raf. This observation argues that the raf gene is a tissue-specific regulator of mRNA levels.     

大鼠纤维化肝组织中PTEN的动态表达及其与肝星状细胞增殖和活化的关系

目的 探讨第10号染色体缺失的磷酸酶张力蛋白同源物基因(PTEN)在大鼠纤维化肝组织中的动态表达及其对在体肝星状细胞(HSC)活化、增殖的影响. 方法 采用胆总管结扎法建立大鼠肝纤维化模型;应用免疫组织化学染色、Western blot和实时荧光定量PCR技术测定大鼠肝组织中PTEN的表达;应用免疫荧光双标记共聚焦激光扫描显微术测定大鼠肝组织中活化HSC的PTEN表达;采用免疫组织化学染色检测大鼠肝组织中α-平滑肌肌动蛋白的表达.结果 免疫组织化学染色显示正常大鼠肝组织中PTEN有广泛表达,主要表达于细胞质,随着肝纤维化的发展,PTEN表达逐渐减少(P<0.01),而α-平滑肌肌动蛋白阳性细胞明显增多(P<0.01);造模1、2、3周及4周不同时间大鼠纤维化肝组织中PTEN的mRNA(分别为假手术组的0.66、0.53、0.44和0.37)及蛋白质表达(吸光度比值分别为1.20±0.13,1.07±0.16,0.88±0.08,0.73±0.07)均低于假手术组(P<0.01),并随着肝纤维化的进展逐渐降低(P<0.01);免疫荧光双标记共聚焦激光扫描显微术显示PTEN在活化HSC广泛表达,主要表达于细胞质,随着肝纤维化的进展,表达PTEN的活化HSC占总的活化HSC的比例逐渐减少(P<0.01). 结论 大鼠纤维化肝组织中PTEN的mRNA及蛋白质表达均下调;在体HSC的PTEN表达亦降低;肝组织中PTEN的动态表达与HSC的活化、增殖呈显著负相关.     

丹黄方对大鼠肝再生过程中PC3、c—fos、LRF—1影响的实验研究

目的：探讨丹黄方对大鼠肝切除肝再生模型中促肝细胞再生的作用机制。方法：采用肝部分切除肝再生模型，用丹黄方进行干预，通过RT-PCR、电泳凝胶等方法检测与肝再生密切相关因子PC3 mRNA、c-fos mRNA、LRF-1 mRNA的表达，观察丹黄方对肝细胞再生的影响。结果：丹黄方对肝再生模型大鼠肝组织PC3 mRNA、c-fos mRNA的表达有增强作用，与模型比较，差异有显著性意义；对肝组织LRF-1 mRNA表达的影响不显著。结论：丹黄方可能是通过增强肝组织PC3 mRNA、c-fosmRNA的表达而促进肝细胞的增殖。     

The mechanisms of hepatic sinusoidal endothelial cell regeneration: A possible communication system associated with vascular endothelial growth factor in liver cells

Vascular endothelial growth factor (VEGF) has been shown to induce proliferation of sinusoidal endothelial cells in primary culture. To elucidate the mechanisms of sinusoidal endothelial cell regeneration in vivo, mRNA expression of VEGF and its receptors, flt-1 and KDR/flk-1, were studied in rat livers. Northern blot analysis revealed that VEGF-mRNA was expressed in hepatocytes immediately after isolation from normal rats. In contrast, non-parenchymal cells, including sinusoidal endothelial cells, expressed VEGF receptor-mRNA. Vascular endothelial growth factor-mRNA expression in hepatocytes was decreased during primary culture, but increased following a peak of DNA synthesis, induced by addition of epidermal growth factor or hepatocyte growth factor to the culture medium at 24 h of plating. In a 70% resected rat liver, VEGF-mRNA expression increased with a peak at 72 h after the operation, and mRNA expression of VEGF receptors between 72 and 168 h. In such a liver, mitosis was maximal in hepatocytes at 36 h and in sinusoidal endothelial cells at 96 h. Also, mRNA expression of both VEGF and its receptors was significantly increased in carbon tetrachloride-intoxicated rat liver compared with normal rat liver. Vascular endothelial growth factor expression was minimal in Kupffer cells isolated from normal rats, but marked in activated Kupffer cells and hepatic macrophages from the intoxicated rats. Vascular endothelial growth factor-mRNA expression was also increased in activated stellate cells from these rats and in the cells activated during primary culture compared with quiescent cells. We conclude that increased levels of VEGF expression in regenerating hepatocytes may contribute to the proliferation of sinusoidal endothelial cells in partially resected rat liver, probably through VEGF receptors up-regulated on the cells. Also, VEGF derived from activated Kupffer cells, hepatic macrophages and stellate cells may be involved in this proliferation in injured rat liver.     

Tumor progression locus 2 (Tpl-2) encodes a protein kinase involved in the progression of rodent T-cell lymphomas and in T-cell activation.

The Tpl-2 locus, cloned by provirus tagging from one of three sublines of the Moloney leukemia virus-induced rat thymoma 2769, defines a gene encoding a protein kinase associated with progression in 22.5% of the tumors. Tpl-2 is expressed primarily in spleen, thymus, liver, and lung. Provirus integration occurs in the last intron of the gene, leading to the expression of a truncated mRNA that terminates in the proviral long terminal repeat and encodes a protein with an altered C-terminal domain. Strong evidence that this genetic change confers growth advantage to affected cell clones was provided by the finding that, during cultivation of all three sublines derived from tumor 2769, cells were selected that harbored independent provirus insertions in the Tpl-2 locus. Exposure of normal rat spleen cells to Con A induces the expression of enhanced levels of Tpl-2 within the first 60 min from the time of exposure suggesting that, in normal splenocytes, Tpl-2 may be involved in the transition from a quiescent to the G1 phase of the cell cycle.     

Evaluation of insulin-like growth factor II, cyclooxygenase-2, ets-1 and thyroid-specific thyroglobulin mRNA expression in benign and malignant thyroid tumours

OBJECTIVE: We evaluated three markers (insulin-like growth factor II (IGF-II), cyclooxygenase-2 (COX-2) and ets-1) of thyroid growth stimulation and cell transformation together with a thyroid-specific marker (thyroglobulin (Tg)) for their potential to differentiate benign and malignant follicular thyroid neoplasia (FN). DESIGN AND METHODS: mRNA expression levels were determined by real-time PCR in 100 snap-frozen thyroid samples: 36 benign thyroid nodules with different histology and function (19 cold (CTN) and 17 toxic thyroid nodules (TTN)), 36 corresponding normal thyroid tissues of the same patients, eight Graves' disease (GD) thyroids, 10 follicular thyroid carcinomas (FTC) and 10 papillary thyroid carcinomas (PTC). RESULTS: Mean IGF-II and COX-2 levels were not significantly altered between benign and malignant thyroid nodules (IGF-II) or nodular (FTC, TTN, CTN) and normal thyroid tissues (COX-2). In contrast, eight- to tenfold upregulation of ets-1 was observed in PTC and three- to fourfold upregulation of ets-1 was observed in FTC (and GD) compared with benign thyroid nodules and normal thyroid tissues. In addition, thyroglobulin mRNA expression was markedly downregulated (50- to 100-fold) in FTC, PTC and GD samples compared with benign nodular and normal thyroid tissues. Hence an ets-1/Tg ratio >20 distinguished differentiated thyroid cancer from benign nodular or normal thyroid tissue. We then studied ets1- and Tg mRNA expression levels in fine needle aspiration cytology (FNAC) samples. However, in a consecutive series of 40 FNAC samples only equivocal results were obtained on 38 benign and two malignant (FTC) thyroid tumour samples. CONCLUSIONS: Upregulation of ets-1 and downregulation of Tg mRNA expression occur in differentiated thyroid cancer and may facilitate pre-operative identification of thyroid malignancy depending on further evaluation of these potentially promising markers in a larger series of benign and malignant thyroid tumours and their FNAC samples.     

Male-enhanced antigen gene is phylogenetically conserved and expressed at late stages of spermatogenesis.

The male-enhanced antigen gene (Mea) was previously isolated from a mouse testicular cDNA library by using a pool of specific antisera against the serological H-Y antigen. The present studies characterize the human and mouse cDNAs and indicate that the MEA gene is conserved at both nucleic acid and protein levels. The corresponding mRNA encodes proteins of 18-20 kDa. The phylogenetic conservation could be extended to other mammalian species by Southern blot analysis. Although the Mea gene was transcribed as a 1-kilobase mRNA in most tissues, it was expressed at the highest level in adult testis. The testis-enhanced expression of the Mea gene was associated with germ cell development at late stages of spermatogenesis. Chromosome walking experiments identified two linked genes, A and B, located within 38 kilobases of human genomic sequence. Like the MEA gene, genes A and B were coordinately transcribed in the testis, which suggests that MEA and genes A and B are members of a gene family. In situ hybridization studies localized the MEA gene to the short arm of human chromosome 6 at band p21.1-21.3, close to the major histocompatibility complex locus. The genetic conservation and testis-specific expression of the MEA gene support the hypothesis that it plays an important role in mammalian spermatogenesis and/or testis development.     

Stem cell and hepatocyte proliferation in hepatitis C cirrhosis and hepatocellular carcinoma: transplant implications

Background. The liver possesses two distinct mechanisms for healing. Wound healing via hepatic stem cells recapitulates early development (hepatoblast proliferation), while liver regeneration resembles late embryonic growth (hepatocyte proliferation). Loss of control over both of these processes have been proposed as mechanisms that may contribute to poor outcomes in HCC.Material and methods. We used microarray gene expression profiles to examine the involvement of hepatic stem cell and hepatocyte proliferation markers and regulators in HCV-induced cirrhosis and HCC. We compared 30 cirrhosis and 49 HCC samples to 12 disease-free control livers.Results. Cirrhosis and HCC expressed markers of stem cell. Inhibitors of hepatocyte proliferation (HP) were highly expressed in cirrhosis. Loss of these HP inhibitors in HCC patients was associated poor prognosis (94 vs. 38% 2-year recurrence- free survival, p = 0.0003). Principal Components Analysis discriminated cirrhotic and HCC tissues, and HCC patients with poor (< 2 year) vs. good (> 2 year) recurrence-free survival. Loss of CDH1 expression correlated with up-regulation of hepatocyte proliferation promoters MET and YAP1. CDH1, MET, and YAP1 were independent predictors of recurrence-free survival by Cox regression when corrected for tumor stage (p < 0.0001).Conclusion. HCV-cirrhosis is characterized by proliferation of liver stem cells and inhibition of hepatocyte proliferation. HCC tumors in which this pattern persists have superior outcomes to those which acquire a hepatocyte proliferation signature. Genes in this signature should be studied further for potential as tissue or serum biomarkers for patient risk stratification. CDH1 and MET are candidates for personalized therapies with targeted pharmaceutical agents.     

S-adenosylmethionine regulates cytoplasmic HuR via AMP-activated kinase

BACKGROUND & AIMS: After liver injury, hepatic S-adenosylmethionine (SAM) content decreases, and the blockage this molecule imposes on hepatocyte proliferation is released, facilitating liver regeneration. This activity of SAM is important for normal liver function because mice deficient in hepatic SAM display abnormal liver regeneration and develop hepatocellular carcinoma. How SAM regulates hepatocyte growth is unclear, but because SAM blocks hepatocyte growth factor (HGF)-induced cyclin D1 expression and DNA synthesis without affecting HGF-induced extracellular signal-regulated kinase phosphorylation, the mitogen-activated protein kinase (MAPK) pathway is probably not the target. METHODS: The effects of SAM on AMPK, HuR localization were assessed in rat hepatocytes after HGF, AICAR, and SAM treatment. RESULTS: We show here that HGF and 5-aminoimidazole-4-carboxamide-riboside (AICAR), an activator of AMP-activated protein kinase (AMPK), induce the phosphorylation of AMPK in hepatocytes and that SAM blocks this process. We also show that HGF- and AICAR-induced AMPK activation stimulate the transport from nucleus to cytoplasm of HuR, an RNA-binding protein that increases the half-life of target mRNA such as cyclin A2, and that SAM blocks this process. We found that, in hepatocytes, AICAR increases HuR binding to cyclin A2 messenger RNA (mRNA) as well as the expression and stability of this mRNA and that SAM blocks these events. Consistently, we found that AICAR induces hepatocyte proliferation and that SAM blocks this effect. Finally, we found that liver AMPK phosphorylation, cytoplasmic HuR, and binding of HuR to HuR-target mRNA and the steady-state levels of these mRNA are increased in knockout mice deficient in hepatic SAM. CONCLUSIONS: Our results yield novel insights about the mechanism by which SAM inhibits cell-cycle progression in the liver.     

A glucose transport protein expressed predominately in insulin-responsive tissues.

Using low-stringency hybridization to the rat brain glucose transporter (GT), a 2489-base-pair cDNA clone was isolated from a rat soleus lambda gt10 cDNA library. It encodes a 509-amino acid protein whose sequence and predicted membrane structure is very similar to those of the rat brain and liver GTs. The muscle GT-like protein is 65% identical in amino acid sequence to the rat brain GT and 52% identical to the rat liver GT; the major differences are in the NH2- and COOH-terminal hydrophilic segments. This GT-like mRNA is expressed predominately in tissues where glucose transport is sensitive to insulin, including striated muscle, cardiac muscle, and adipose tissue; low-level expression is also detected in smooth muscle and kidney mRNA. This GT-like cDNA is the fourth member of the mammalian GT-related gene family identified to date. We propose that it encodes an insulin-sensitive GT.     

Heme oxygenase-1 is an antifibrogenic protein in human hepatic myofibroblasts

BACKGROUND & AIMS: Hepatic myofibroblasts play a key role in the development of liver fibrosis associated with chronic liver diseases. We have shown that oxidative stress is a messenger of 15-deoxy-delta-12,14-prostaglandin J2 (15-d-PGJ2) in human hepatic myofibroblasts. The aim of the present study was to investigate the role of a stress-inducible protein, heme oxygenase-1 (HO-1), in the action of 15-d-PGJ2. METHODS: Expression of HO-1 was characterized in biopsy specimens of normal human liver and active cirrhosis by immunohistochemistry, and in cultured human hepatic myofibroblasts by Northern and Western blot analysis. Functional studies also were performed in cultured human hepatic myofibroblasts. RESULTS: Immunohistochemistry showed that in biopsy specimens from normal livers, HO-1 protein expression was restricted to Kupffer cells. Biopsy specimens from cirrhotic patients displayed HO-1 protein both in macrophages and in myofibroblasts within fibrotic septa. HO-1 messenger RNA (mRNA) and protein also were detected in cultured human hepatic myofibroblasts and increased in response to 15-d-PGJ2 in a time- and dose-dependent manner. Induction of HO-1 in human hepatic myofibroblasts mediated 2 major antifibrogenic properties of 15-d-PGJ2, namely, inhibition of proliferation and of procollagen I mRNA expression. These effects were ascribed to bilirubin, one of the products of HO-1-mediated heme degradation. CONCLUSIONS: This study shows that HO-1 is expressed in human hepatic myofibroblasts and induced during chronic liver injury. Moreover, these data unravel HO-1 as a major antifibrogenic pathway.     

肝再生增强因子在肝癌细胞中的表达及意义

目的研究肝再生增强因子(ALR)对肝癌细胞和原代大鼠肝细胞增殖作用的影响及在肝细胞癌(HCC)中的表达。方法将不同种属的ALR分别与原代大鼠肝细胞和人肝癌细胞株QGY和HepG2共同培养后，用^3H-胸腺嘧啶核苷掺入法测定这些细胞的增殖情况。并应用免疫组织化学法对9例正常肝组织和21例HCC组织中ALR的表达进行了研究。结果不同种属的ALR在体外均能刺激人肝癌细胞株QGY和HepG2增殖，并呈剂量依赖关系，但对原代大鼠肝细胞均无刺激增殖作用。在正常肝组织中ALR不表达，但在HCC肝组织中ALR均表达，且ALR的表达程度与HCC分化程度和大小均无关。结论ALR可能在HCC的发生发展中起着重要作用。     

Kupffer cells are mandatory for adequate liver regeneration by mediating hyperperfusion via modulation of vasoactive proteins

OBJECTIVE: Physiological liver regeneration requires adequate microvascular perfusion after partial hepatectomy. Although Kupffer cells (KCs) are known to play a key role in modulating hepatocyte proliferation, their impact on regulating hepatic microcirculation during liver regeneration has so far been disregarded. With respect to their expression and modulation of vasoactive mediators, KCs may provide important signals that regulate hepatic perfusion during liver regeneration. METHODS: Intravital fluorescence microscopy, immunohistochemistry, Western blot analysis, and RT-PCR were used to analyze livers of KC-depleted mice (liposome-encapsulated clodronate application) and KC-competent mice at days 3, 5, and 8 after 68% hepatectomy. RESULTS: Selective and long-lasting KC elimination limited the resection-associated hyperperfusion, as evidenced by an only 1.7- to 2-fold increase of sinusoidal volumetric blood flow and shear stress in contrast to a 3.5- to 5-fold increase in KC-competent mice. In accordance to that livers of KC-depleted mice showed an altered pattern of vasoregulatory gene expression. KC-depleted mice failed to show resection-induced increase of HO-1 and eNOS protein expression, but revealed a reduction of hepatic eNOS and HO-1 protein levels to 22 and 12% of the corresponding values in KC-competent mice. In addition, the eNOS inhibitory protein caveolin-1 was increased in KC-depleted animals prior to as well as after resection. Furthermore, resection-associated accumulation of ET-1 mRNA was absent in KC-depleted livers. Finally, liver mass restoration was impaired, with a regain of only 79% weight within 8 days after resection in KC-depleted mice. CONCLUSION: The present study documents a remarkable change of the vasoactive mediator profile upon KC-depletion and liver resection, limiting intrahepatic hyperperfusion. Therefore, KC-dependent molecular mechanisms seem to be mandatory in regulating vasotonus during the process of liver regeneration and therewith maintaining intrahepatic shear stress as a trigger of hepatic proliferation.     

Regulation of hepatic transport systems involved in bile secretion during liver regeneration in rats.

We investigated the expression of hepatic transport systems involved in bile secretion during liver regeneration after partial hepatectomy (PH) in rats. Initial studies showed maximal BrdU incorporation 24 hours after PH. Therefore, transporter expression and bile secretion were analyzed in detail at this time. The mRNA levels of the multidrug resistance genes mdr1a and mrp1 slightly increased, whereas mdr1b mRNA levels showed an extensive increase after PH. The mRNA levels of the conjugate transporter, mrp2, decreased slightly, whereas mrp2 protein levels did not change. Bilirubin secretion did not change, but the biliary glutathione secretion markedly decreased and the hepatic GSH content increased. The messenger RNA levels of the bile salt uptake transporters ntcp, oatp1, and oatp2 and the bile salt exporter, bsep/spgp, all decreased with ntcp showing the most prominent decrease. Protein levels of ntcp dramatically decreased whereas oatp2 only slightly decreased. Oatp1 protein expression slightly increased and bsep/spgp protein levels did not change. Decreased levels of bile salt uptake systems were associated with a 10-fold increase in the plasma bile salt concentration, yet, bile flow and bile salt secretion were increased when expressed per gram liver and unaffected when expressed on the basis of body weight. In conclusion, during the initial phase of rat liver regeneration ntcp is down-regulated whereas other transporter proteins involved in bile secretion are only slightly affected. Despite increased serum bile salt levels the remnant liver is not cholestatic: bile flow is maintained by uptake of bile salts probably via oatp isoforms and their secretion via bsep/spgp.