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T Niki

Publications and source records attributed to T Niki.

At least 37 records · Page 2Linked to original sources
PubMed2000

MSSP promotes ras/myc cooperative cell transforming activity by binding to c-Myc.

BACKGROUND: MSSPs, myc single strand binding proteins, were originally identified as proteins recognizing a putative replication origin/transcriptional enhancer in the human c-Myc gene. The cDNAs encoding four of the family proteins, MSSP-1, MSSP-2, Scr2 and Scr3, were cloned. These proteins carry two copies of the putative RNA binding domains, RNP-A and RNP-B, and have been suggested to participate in DNA replication and cell cycle progression from the G1 to the S phase. RESULTS: We report that MSSP-1 and MSSP-2 bound directly to the C-terminal portion of c-Myc, along with Max, side by side. MSSP, c-Myc and Max formed a ternary complex in vivo, although MSSP did not directly associate with Max. The MSSP/Myc/Max ternary complex lost the binding activity to the E-box sequence-the recognition sequence of c-Myc/Max complex-thereby abrogating the E-box-dependent transcription activity of c-Myc. MSSP specifically stimulated the cooperative transforming activity of c-myc with ras, in a manner dependent upon the RNP sequences, while mssp itself showed no transforming activity in mouse NIH3T3 cells. The NIH3T3 transformants, together with ras, myc and mssp, grew to form very large colonies in soft agar, as compared to those with ras plus myc or ras alone. CONCLUSIONS: MSSP is a modulator of c-Myc and the c-Myc/MSSP complex may deregulate cell cycle controls and lead cells towards transforming pathways.

3T3 Cells↗
PubMed2000

Lung carcinoma with polypoid growth in the main pulmonary artery: report of two cases.

Invasion into the lumen of the main pulmonary artery is an uncommon mode of extension in lung carcinoma and its prognostic significance remains unclear. We describe here two resected cases of lung carcinoma that showed such a rare tumor spread. Although a preoperative evaluation, such as angiography or perfusion scan of the lung, had shown a significant decrease in circulation, we could not diagnose the intraluminal tumor growth preoperatively. Pneumonectomy was finally needed to perform a curative operation. The tumors were centrally located and showed polypoid growth in the main pulmonary artery. Postoperative pathological examination revealed the tumors to be adenosquamous carcinoma of the lung in both cases. No intrapulmonary metastases were detected. One patient is doing well with no signs of recurrence after a follow-up period of 10 years. Although intra-arterial polypoid growth of lung carcinoma is extremely rare, such tumor extension should be considered preoperatively to perform a curative surgical resection, especially when the tumor is centrally located. While arterial invasion is generally an ominous prognostic factor, curative surgical resection would offer a good prognosis, even for lung carcinoma invading the main pulmonary arterial trunk.

Aged↗
PubMed2000

New aspects of sterol carrier protein 2 (nonspecific lipid-transfer protein) in fusion proteins and in peroxisomes.

Sterol carrier protein 2 (SCP2) is a 13-kDa peroxisomal protein, identical to nonspecific lipid-transfer protein, and stimulates various steps of cholesterol metabolism in vitro. Although the name is reminiscent of acyl carrier protein, which is involved in fatty acid synthesis, SCP2 does not bind to lipids specifically or stoichiometrically. This protein is expressed either as a small precursor or as a large fusion (termed SCPx) that carries at its C-terminal the complete sequence of SCP2. SCPx exhibits 3-oxoacyl-CoA thiolase activity, as well as sterol-carrier and lipid-transfer activities. The N- and C-terminal parts of SCPx are similar to the nematode protein P-44 and the yeast protein PXP-18, respectively. P-44, which has no SCP2 sequence, thiolytically cleaved the side chain of bile acid intermediate at a rate comparable to that of SCPx. This, together with the properties of other fusions with SCP2-like sequence, suggests that the SCP2 part of SCPx does not play a direct role in thiolase reaction. PXP-18, located predominantly inside peroxisomes, is similar to SCP2 in primary structure and lipid-transfer activity, and protects peroxisomal acyl-CoA oxidase from thermal denaturation. PXP-18 dimerized at a high temperature, formed an equimolar complex with the oxidase subunit, and released the active enzyme from the complex when the temperature went down. This article attempts to gain insight into the role of SCP2, and to present a model in which PXP-18, a member of the SCP2 family, functions as a molecular chaperone in peroxisomes.

Animals↗
PubMed2000

Expression of vascular endothelial growth factors A, B, C, and D and their relationships to lymph node status in lung adenocarcinoma.

Vascular endothelial growth factors (VEGFs) C and D are novel members of the VEGF family that show some selectivity toward lymphatic endothelial cells. Recent studies suggest that VEGF-C may be involved in lymphangiogenesis and spread of cancer cells via lymphatic vessels. However, whether other VEGF family members play a role in lymph node metastasis is largely unknown. The aim of the present study was to explore whether expressions of VEGF-A, VEGF-B, VEGF-C, and VEGF-D are correlated with lymph node status in lung adenocarcinoma. Total RNA was isolated from 60 surgical specimens of lung adenocarcinoma with (n = 27) or without (n = 33) lymph node metastasis. The relative mRNA abundance of VEGF-A, VEGF-B, VEGF-C, and VEGF-D was measured by real-time reverse transcription-PCR analysis based on TaqMan fluorescence methodology. We found that, as single factors, expression of none of the four VEGF family members clearly correlated with the presence of lymph node metastasis. The only tendency noted was for higher VEGF-B and VEGF-C and lower VEGF-D levels in the node-positive group. However, two-way scatterplot analysis revealed that tumors with lymph node metastasis were associated with a pattern of low VEGF-D and high VEGF-A, VEGF-B, or VEGF-C, such that the ratios of VEGF-D:VEGF-A, VEGF-D:VEGF-B, or VEGF-D:VEGF-C were significantly lower in the node-positive group. Strikingly, none of the 11 tumors with high VEGF-D levels metastasized to lymph nodes. Furthermore, a low VEGF-D:VEGF-C ratio correlated with the presence of lymphatic invasion, and six of seven tumors with a pattern of very high expression of VEGF-C and low expression of VEGF-D displayed lymph vessel invasion that extended along the bronchovascular tree beyond the main tumor. Finally, levels of VEGF-A, but not VEGF-B or VEGF-C, were higher in tumors with large nodal metastasis (> or = 1 cm) than in those with small (< 1 cm) nodal metastasis. These results support the hypothesis that two VEGF family members are involved in lymph node metastasis at two distinct steps; VEGF-C facilitates entry of cancer cells into the lymph vasculature, whereas VEGF-A promotes the growth of metastatic tumor through angiogenesis. The results also suggest that the balance between VEGF-C and VEGF-D could be important rather than the level of VEGF-C alone. Whether a low VEGF-D level plays a causative role in lymph node metastasis requires further investigation.

Adenocarcinoma↗
PubMed1999

Differential expression patterns of inositol trisphosphate receptor types 1 and 3 in the rat suprachiasmatic nucleus.

Inositol 1,4,5-trisphosphate receptor types 1 (IP(3)-R1) and 3 (IP(3)-R3) were found in the rat suprachiasmatic nucleus (SCN) and the levels of both of IP(3)-R1 and IP(3)-R3 mRNA showed a reciprocal circadian rhythm. IP(3)-R1 immunoreactive cells were localized in neuronal cells in the SCN. In contrast, IP(3)-R3 immunoreactive cells were mainly localized in the astrocytes in the ventrolateral region of the SCN. These results suggest that IP(3)-R1 and IP(3)-R3 may have differential roles in the SCN in the mammalian circadian rhythm.

Animals↗
PubMed1999

Clinocopathologic significance of laminin-5 gamma2 chain expression in squamous cell carcinoma of the tongue: immunohistochemical analysis of 67 lesions.

BACKGROUND: The laminin-5 gamma2 chain plays an important role in cell migration during tumor invasion and tissue remodeling. METHODS: Laminin-5 gamma2 chain expression in squamous cell carcinomas of the tongue in 67 patients with Stage II, III, or IVA,B (excluding the cases with distant metastasis) was examined immunohistochemically to determine its associations with the clinicopathologic features of each tumor. The predominant staining patterns were categorized as follows: A, few or no tumor cells were positive; B, part of the tumor nest periphery was positive; C, the tumor nest periphery was circumferentially positive; or D, almost all the tumor cells were positive. RESULTS: Laminin-5 gamma2 chain expression was observed clearly in tumor cell cytoplasm. Of the 67 tumors examined, 6 (9%), 31 (46%), 19 (28%), and 11 (17%) showed staining patterns A, B, C, and D, respectively. With progression from staining pattern A to D, the number of immunopositive tumor cells increased significantly (P<0.0001), and the tumor histology showed significantly more infiltrative growth (P<0.0001) and poorer differentiation (P = 0.0021). Furthermore, both univariate (P = 0.0019) and multivariate (P = 0.0003; hazard ratio = 3.132) analysis of the patients' survival revealed that the prognosis became significantly poorer with progression from staining pattern A to D. CONCLUSIONS: Increased laminin-5 gamma2 chain immunoreactivity, which may reflect a high invasive potential of cancer cells, is a factor indicative of a poor prognosis for patients with squamous cell carcinoma of the tongue.

Adult↗
PubMed1999

The expression of the melatonin synthesis enzyme: arylalkylamine N-acetyltransferase in the suprachiasmatic nucleus of rat brain.

The hormone melatonin, secreted primarily from the pineal gland, plays an important physiological role in synchronizing biological rhythms and neuroendocrine. Presently, we find the expression of the serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase, AA-NAT) mRNA, the rate-limiting enzyme in the conversion of serotonin to melatonin, in the rat suprachiasmatic nucleus (SCN) which contains the biological circadian clock in mammals. AA-NAT mRNA content in rat SCN did not show a significant circadian rhythm. However, AA-NAT enzyme activity was lowest at midday and highest at early night, and the rhythm persisted under constant dark conditions. These results indicate that the rat SCN is capable of synthesizing melatonin and suggest that melatonin synthesis in the SCN may be regulated by the circadian clock at the post transcriptional level.

Animals↗
PubMed1999

Class VI intermediate filament protein nestin is induced during activation of rat hepatic stellate cells.

Hepatic stellate cells are considered to be liver-specific pericytes that play a key role in liver fibrosis. Because these cells express desmin and smooth muscle alpha-actin, they were assumed to be of myogenic origin. This hypothesis became doubtful when it was reported that stellate cells also express glial fibrillary acidic protein and neural cell adhesion molecule. In the present study, we show that activated stellate cells express nestin, a class VI intermediate filament protein originally identified as a marker for neural stem cells. Expression of nestin was first studied during spontaneous activation of stellate cells in culture. Immunohistochemistry showed that nestin-positive stellate cells already appeared at day 3, and nearly all the cells became positive for nestin at day 6 and 15. The immunoreaction was present in filaments except in dividing cells. The presence of messenger RNA transcript for nestin was shown by reverse transcription polymerase chain reaction and sequencing of amplified complementary DNA. We then compared the presence of nestin with that of other intermediate filament proteins and smooth muscle alpha-actin. Immunoblotting showed that the relative concentrations of nestin, desmin, and vimentin increased between day 2 and 6 in primary culture. After the initial increase vimentin leveled off, while nestin and desmin showed a tendency to decrease. This pattern was quite different from that of glial fibrillary acidic protein, which kept declining, and smooth muscle alpha-actin, which increased continuously up to day 13 in culture. We then studied the presence of nestin in normal and CCl4-injured rat liver. In normal liver, minimal immunoreaction for nestin was observed within the liver parenchyma. During induction of fibrosis by carbon tetrachloride, nestin-positive stellate cells appeared at 6 weeks, which was late in comparison with the induction of desmin and smooth muscle alpha-actin. We conclude that nestin is induced in stellate cells during transition from the quiescent to the activated phenotype; culture activation is a stronger stimulus than in vivo activation by injection of CCl4. Taken together with reports on expression of glial fibrillary acidic protein and neural cell adhesion molecule by stellate cells, new experimental studies on the embryonic origin of these cells are required.

Actins↗
PubMed1999

A histone deacetylase inhibitor, trichostatin A, suppresses myofibroblastic differentiation of rat hepatic stellate cells in primary culture.

Hepatic stellate cells are the major cellular sources of extracellular matrix in chronic liver diseases leading to fibrosis. We explored the antifibrogenic effect of two histone deacetylase inhibitors, sodium butyrate and trichostatin A (TSA), on this cell type in vitro. Primary hepatic stellate cells as well as culture activated cells were exposed to butyrate (0.01-1 mmol/L) or TSA (1-100 nmol/L); their effect on collagen types I and III and smooth muscle alpha-actin was examined by quantitative immunoprecipitation and by Northern analysis. Their antiproliferative effect was examined by 3H-thymidine incorporation and cell counting. Hyperacetylation of histones was demonstrated by acid urea/Triton-X-100 (AUT) polyacrylamide gel electrophoresis. Possible cytotoxic effects were judged on stellate cells by evaluating de novo total protein synthesis, and on hepatocytes by measuring lactate dehydrogenase (LDH) leakage, albumin secretion, and epoxide hydrolase and ethoxycoumarin O-deethylase activity. TSA at 100 nmol/L and butyrate at 1 mmol/L retarded the morphological changes characteristic for activation of primary stellate cells. TSA at 100 nmol/L inhibited synthesis of collagen types I and III and smooth muscle alpha-actin by 62%, 70%, and 88%. Butyrate at 1 mmol/L showed a modest inhibitory effect on collagen type III and smooth muscle alpha-actin, but had no effect on collagen type I. Northern analysis suggested that these inhibitory effects on collagen type III and smooth muscle alpha-actin were transcriptional, while the effect on collagen type I was largely posttranscriptional. At 100 nmol/L, TSA strongly suppressed proliferation of primary hepatic stellate cells. Inhibition of activation of stellate cells was preceded by hyperacetylation of histone H4. When tested on cells at day 14 in culture, butyrate had no inhibitory effects on the synthesis of collagens or smooth muscle alpha-actin. One hundred or 10 nmol/L TSA modestly inhibited the synthesis of collagens type I (-24%,-22%) and III (-34%,-22%), and smooth muscle alpha-actin (-27%,-12%). We conclude that TSA inhibits transdifferentiation of stellate cells into myofibroblasts by interfering with the level of acetylation of histone H4.

Actins↗
PubMed1999

Administration of G-CSF to normal individuals diminishes L-selectin+ T cells in the peripheral blood that respond better to alloantigen stimulation than L-selectin- T cells.

To determine whether administration of G-CSF induces phenotypic or functional changes in T cells, we examined peripheral blood T cells from normal individuals receiving G-CSF for activation antigen and adhesion molecule expression before and after G-CSF administration. G-CSF (10 microg/kg/day) was administered subcutaneously to 14 normal individuals for 3-5 days and their PBMC were serially analyzed with monoclonal Ab (mAb) directed to HLA-DR, CD45RO, CD45RA, CD25, CD122, CD95, CD11a, CD49d, CD44 and CD62L (L-selectin) coupled with anti-CD3 mAb. Among T cells positive for these antigens, only the proportion of T cells expressing L-selectin significantly decreased from 68% to 37% after 3-day G-CSF administration. When peripheral blood CD3+ T cells obtained before and after G-CSF administration were sorted into two populations depending on the expression of L-selectin and tested for their proliferative response to allogeneic B cells, the reactivity of L-selectin- cells to alloantigen stimulation was consistently lower than that of L-selectin+ cells regardless of the exposure to G-CSF. The decrease in the relative number of L-selectin+ cells induced by G-CSF administration may contribute to the unexpectedly low incidence of severe acute GVHD after allogeneic PBSC transplantation.

Granulocyte Colony-Stimulating Factor↗
PubMed1998

Mouse MD-1, a molecule that is physically associated with RP105 and positively regulates its expression.

RP105 is a leucine-rich repeat molecule that is expressed on mouse B cells and transmits a growth-promoting signal. An anti-RP105 Ab precipitated additional molecules as well as RP105. These molecules were found to be a mouse homologue of chicken MD-1. Chicken MD-1 was previously isolated as a v-myb-regulated gene, since its transcription increases rapidly after v-myb induction. Mouse MD-1, when transiently expressed as an epitope-tagged protein, is secreted in culture fluid but tethered to the cell surface by coexpressed RP105. An association of these molecules was confirmed by immunoprecipitation with the anti-RP105 Ab and subsequent probing of the epitope tag on MD-1. Moreover, MD-1 has an effect on the expression of RP105. In transient transfection of RP105, the percentage of RP105-positive cells increased more than twice with the coexpression of MD-1. The stable expression of MD-1 conferred approximately a sevenfold increase in cell surface RP105 on a cell line that expresses RP105 alone. Thus, MD-1 is physically associated with RP105 and is important for efficient cell surface expression.

Amino Acid Sequence↗
PubMed1998

Inhibition of insulin-induced GLUT4 translocation by Munc18c through interaction with syntaxin4 in 3T3-L1 adipocytes.

Insulin induces the translocation of vesicles containing the glucose transporter GLUT4 from an intracellular compartment to the plasma membrane in adipocytes. SNARE proteins have been implicated in the docking and fusion of these vesicles with the cell membrane. The role of Munc18c, previously identified as an n-Sec1/Munc18 homolog in 3T3-L1 adipocytes, in insulin-regulated GLUT4 trafficking has now been investigated in 3T3-L1 adipocytes. In these cells, Munc18c was predominantly associated with syntaxin4, although it bound both syntaxin2 and syntaxin4 to similar extents in vitro. In addition, SNAP-23, an adipocyte homolog of SNAP-25, associated with both syntaxins 2 and 4 in 3T3-L1 adipocytes. Overexpression of Munc18c in 3T3-L1 adipocytes by adenovirus-mediated gene transfer resulted in inhibition of insulin-stimulated glucose transport in a virus dose-dependent manner (maximal effect, approximately 50%) as well as in inhibition of sorbitol-induced glucose transport (by approximately 35%), which is mediated by a pathway different from that used by insulin. In contrast, Munc18b, which is also expressed in adipocytes but which did not bind to syntaxin4, had no effect on glucose transport. Furthermore, overexpression of Munc18c resulted in inhibition of insulin-induced translocation of GLUT4, but not of that of GLUT1, to the plasma membrane. These results suggest that Munc18c is involved in the insulin-dependent trafficking of GLUT4 from the intracellular storage compartment to the plasma membrane in 3T3-L1 adipocytes by modulating the formation of a SNARE complex that includes syntaxin4.

3T3 Cells↗
PubMed1998

The localization of the site of arylalkylamine N-acetyltransferase circadian expression in the photoreceptor cells of mammalian retina.

To investigate the molecular mechanism of the melatonin rhythm in the mammalian retina, we examined the temporal mRNA expression pattern of arylalkylamine (serotonin) N-acetyltransferase (AA-NAT), the rate-limiting enzyme in melatonin synthesis in the rat retina. Rat AA-NAT mRNA was detected exclusively in the retinal photoreceptors in the outer nuclear layer--low during the day and increased more than threefold at night. The nocturnal AA-NAT expression in rat retina was also confirmed by RNase protection and the AA-NAT enzymatic activity. This is the first report to localize the site of AA-NAT mRNA circadian expression in mammalian photoreceptor cells.

Animals↗
PubMed1998

Purification of rat hepatic stellate cells by side scatter-activated cell sorting.

In this study, we present a new method to obtain pure, viable, freshly isolated hepatic stellate cells. Stellate cells were purified by cell sorting using their high side scatter (SSC) of incident light. Purity of the cells was established by light and transmission electron microscopy (TEM). Starting from stellate cells that were 50% to 70% enriched by centrifugation in 11% Nycodenz, the cell purity after sorting was found to be 96.6% +/- 2.9%. Viability of the sorted cells was 90.8% +/- 2.2% as measured by the Trypan blue exclusion test and was confirmed by cell culturing. Per hour of sorting, 1.4 +/- 0.4 million stellate cells were obtained. Sorting runs of up to 4 hours were practically feasible, resulting in yields of 5 to 6 million cells per rat liver. Cells attached to plastic substratum within 24 hours. Subsequently, they spread and underwent spontaneous transition into myofibroblast-like cells. The purity of sorted cells was documented by reverse-transcriptase polymerase chain reaction (RT-PCR) experiments using specific primer pairs for messenger RNA (mRNA) species that were only present in parenchymal (preproalbumin), endothelial (endothelial cell nitric oxide synthase [eNOS]), stellate (desmin), or Kupffer cells (77- to 88-kd fucose receptor). Contaminating mRNA species were absent in sorted stellate cells. Next, we examined freshly sorted stellate cells by Western blotting to confirm the presence of relevant cytoskeletal proteins. Cells were positive for vimentin, desmin, and glial fibrillary acidic protein (GFAP), but negative for alpha-smooth muscle actin (alpha-SMA). Sorted and cultured cells were immunophenotyped for the presence of collagen types I, III, and IV, laminin, and the cytoskeletal proteins, alpha-SMA, desmin, vimentin, and GFAP. At 90 hours in culture, cells expressed all the investigated extracellular matrix proteins. Desmin was present in 82% +/- 1%, vimentin in 96% +/- 2.5%, and GFAP in 91% +/- 4.5% of cells. Alpha-SMA was present in 91% +/- 2% of cultured cells. We conclude that cell sorting based on SSC of incident light is a convenient method to obtain virtually pure stellate cells that can be used for direct analysis or for culturing. Although the yields obtained with this method are lower than with standard methods, and additional equipment is required, SSC-activated sorting offers the possibility of very pure cells when essential for analyses based on sensitive detection methods such as RT-PCR.

Albumins↗
PubMed1998

Second primary rhabdomyosarcomas in patients with bilateral retinoblastoma: a clinicopathologic and immunohistochemical study.

We reviewed six cases of rhabdomyosarcoma as a rare second primary malignancy in children with bilateral retinoblastoma after irradiation treatment. The patients comprised four females and two males (age range 1 year 4 months-7 years 11 months). Second tumors arose in the temporal muscle inside or close to the previously irradiated fields. All the children were alive and well 24-72 months after diagnosis. Microscopic examination showed proliferation of closely packed, small round cells with scanty cytoplasm, coarse nuclear chromatin, and increased mitotic activity without a myxoid background nor obvious alveolar architecture. The most characteristic feature was the presence of rosette-like structures in four tumors. Immunoreactivity for many skeletal muscle markers was evident, including desmin (six of six), muscle-specific actin (HHF35) (six of six), sarcomeric actin (six of six), myogenin (six of six), vimentin (six of six), and myoglobin (three of six). On reverse transcriptase-polymerase chain reaction examination, three second tumors lacked specific chimeric transcripts for alveolar rhabdomyosarcoma and Ewing's sarcoma. Unexpectedly, variable reactivity for neurofilament (150 kd) was identified in six of six second tumors as well as 15 of 20 sporadic primary rhabdomyosarcomas (75%) examined as controls, the result being confirmed by Western blot analysis. In addition, staining for retinoblastoma-susceptibility gene protein was negative in all second tumors, in contrast to positivity in 14 of 17 sporadic primary tumors (82%). This finding suggests that retinoblastoma-susceptibility gene abnormalities could be associated with the development of second primary rhabdomyosarcoma. We consider that knowledge of the occurrence of rhabdomyosarcoma and appropriate immunohistochemical study are helpful for avoiding a misdiagnosis of recurrent retinoblastoma or Ewing's sarcoma when encountering patients with a history of bilateral retinoblastoma who developed second small round cell neoplasms.

Antigens, Neoplasm↗
PubMed1997

Inhibition of the binding of SNAP-23 to syntaxin 4 by Munc18c.

SNARE proteins have been implicated in the insulin-induced translocation of vesicles containing the GLUT4 glucose transporter to the plasma membrane of adipocytes. The role of the target SNARE SNAP-25 or its homologs in this process was investigated by screening a mouse adipocyte cDNA library with rat SNAP-25 and human SNAP-23 cDNA probes. Both positive clones isolated encoded a protein with 87% sequence identity to human SNAP-23, and which was therefore designated mouse SNAP-23. Immunoblot and immunofluorescence analyses revealed that SNAP-23 is located predominantly in the plasma membrane of 3T3-L1 adipocytes incubated in the absence or presence of insulin. Of syntaxins 1 to 5, SNAP-23 bound with the highest affinity to syntaxins 1 and 4 in the yeast two-hybrid system. Expression of SNAP-23, syntaxin 4, and the syntaxin-binding protein Munc 18c in COS cells revealed that Munc18c reduced the amount of SNAP-23 bound to syntaxin 4 in a concentration-dependent manner. These results suggest that the binding of SNAP-23 to syntaxin 4 is inhibited by Munc18c in adipocytes.

Adipocytes↗
PubMed1997

Gene expression and synthesis of fibronectin isoforms in rat hepatic stellate cells. Comparison with liver parenchymal cells and skin fibroblasts.

Fibronectins are multifunctional glycoproteins that are important components of the extracellular matrix in normal and fibrotic liver. Multiple fibronectin isoforms are generated from a single gene by alternative splicing of the primary transcript at the domains EIIIA, EIIIB, and V. The aim of this study was to investigate the fibronectin isoforms expressed by activated hepatic stellate cells, the most important connective tissue-producing cells in injured liver. Hepatocytes and skin fibroblasts were also studied for comparison. Activation of hepatic stellate cells in vivo was induced by injecting CCl4 twice weekly for 3 weeks. Activation in vitro was achieved by culturing cells on plastic. The level of activation was evaluated by alpha-smooth muscle actin immunocytochemistry. Steady-state levels of fibronectin isoform messenger RNA were examined by Northern hybridization analysis using specific cDNA probes for the EIIIA, EIIIB, and V domains. The de novo synthesis of fibronectin isoforms was examined by metabolic labelling and immunoprecipitation using domain-specific monoclonal antibodies. Fibronectin transcripts were not detectable in freshly isolated hepatic stellate cells from normal liver. Cultured hepatic stellate cells, as well as skin fibroblasts, expressed EIIIA+, EIIIB+, and V95+ transcripts. They were detectable as early as day 3 and increased with time in culture. At 3 days in culture, more than 90 per cent of stellate cells were alpha-smooth muscle actin-positive. In vivo activated hepatic stellate cells expressed EIIIA+ and V95+ transcripts; EIIIB+ fibronectin mRNA was absent. Less than 20 per cent of in vivo activated stellate cells expressed alpha-smooth muscle actin. Freshly isolated parenchymal cells from normal liver as well as from CCl4-treated liver expressed V95+ transcripts, but were negative for EIIIA or EIIIB fibronectin mRNA. Immunoprecipitation results were in accordance with Northern hybridization analysis. Hepatic stellate cells in culture synthesized and secreted fibronectin molecules that contained EIIIA, EIIIB, and V fragments. Our results indicate that hepatic stellate cells synthesize and secrete fibronectin isoforms that are distinct from those of parenchymal cells.

Animals↗