Glycosaminoglycans and proteoglycans induce gap junction expression and restore transcription of tissue-specific mRNAs in primary liver cultures

Differential requirements for cell-specific elastase I enhancer domains in transfected cells and transgenic mice

The 134-bp enhancer region of the pancreatic elastase I gene is sufficient to direct pancreatic acinar cell-specific transcription in transgenic mice and in transfected cells in culture. Ten-base-pair scanner mutations in three separate enhancer domains that inactivate enhancer function in transfected pancreatic cells in culture have no significant effect in transgenic mice. Because any pair of the three domains is sufficient to direct pancreas-specific expression in mice, no one domain is required for pancreas-specific transcription. Disruption of any two domains does inactivate the enhancer function in transgenic mice. Therefore, the elastase I enhancer domains essential for function in transfected cells in culture are not essential in animals but have a redundant function not apparent in transfected cells. This redundant function is not because of the particular acinar cell line used for transfections, the nature of the reporter gene, or the state of integration of the foreign test gene. We conclude that a trans-acting transcription factor or a modification of a factor(s) present in pancreatic cells of an animal is absent in pancreatic acinar cell lines.

The in vitro unscheduled DNA synthesis (UDS) assay in rat primary hepatocytes. Validation of improved methods for primary culture including data on the lack of effect of ionizing radiation

The in vitro unscheduled DNA synthesis (UDS) assay was evaluated for inclusion in a battery of assays used at The Upjohn Company for evaluation of lead compounds in the development of new and existing drug entities. This evaluation process encompassed aspects of the isolation of hepatocytes and tests of reference mutagens and genotoxins. The flow rate of perfusion solutions and their temperatures were critical in the isolation of high viability hepatocytes in good yield. The attachment of freshly isolated hepatocytes to coverslips was greatly enhanced by coating the coverslips with type III collagen. Results of testing 12 known genotoxic agents (UV light, cyclophosphamide, 7,12-dimethylbenzanthracene, dimethylnitrosamine, diethylnitrosamine, 2-acetylaminofluorene, benzo[a]pyrene, methyl methanesulfonate, ethyl methanesulfonate, N-propyl-N'-nitro-N-nitrosoguanidine, benzidine and 4-aminobiphenyl) were in agreement with the literature. The use of X-ray did not induce unscheduled DNA synthesis in hepatocytes. This latter finding draws attention to the inability of this assay to detect agents which result in 'short-patch' repair of damage.

Maintenance of alcohol dehydrogenase activity in long-term culture of hepatocytes from female rat

Conditions for maintaining the activity of alcohol dehydrogenase in cultures of hepatocytes isolated from female rats were studied. The activity of alcohol dehydrogenase in freshly isolated cells was 1.7 U/mg DNA. When cultured, the activity declined 20% after one day of culture, irrespective of the culture conditions. In a conventional medium with 5 mM glucose the activity after one week of culture was only 30% of that initially measured in culture. Addition of 25 mM glucose or a high concentration of amino acids delayed the decrease. When these compounds were added together it was possible to maintain the initial activity for one week, but the activity declined during the following week. Addition of growth hormone had no effect during the first week of culture but abolished the fall during the second week. The initial metabolism of ethanol was 0.65 mumol/min x mg DNA and declined to two-thirds during the 2 weeks of culture.

Sex change in cytochrome P-450 phenotype by growth hormone treatment of adult rat hepatocytes maintained in a culture system on matrigel

Results of studies of hypophysectomized rats suggest that growth hormone serves as a final common mediator through which gonadal steroids and other modifiers of pituitary function alter the expression of gender-specific liver genes such as the sexually dimorphic pair of cytochrome P-450 isozymes, male-specific P-450h and female-specific P-450i. We tested the effects of growth hormone in a system for primary monolayer culture of adult rat hepatocytes on a laminin-rich extracellular matrix (matrigel), which permits sustained expression of both constitutive and inducible liver genes in a chemically defined medium. Cultures of freshly isolated hepatocytes prepared from untreated male rats and samples of the intact donor liver contained readily detectable quantities of immunoreactive P-450h protein (measured on immunoblots of cell microsomes) and P-450h mRNA (measured on Northern blots of cellular RNA). Neither P-450i immunoreactive protein nor P-450i mRNA were present. Addition of physiologic concentrations of human or bovine growth hormone, but not of prolactin, to culture medium lacking insulin or other hormones resulted in prompt induction of P-450i immunoreactive protein and P-450i mRNA. Induction of P-450i mRNA in male hepatocyte cultures was dependent on the concentration of growth hormone, required as little as 24 hr of exposure, and was markedly attenuated in cultures maintained on type I collagen rather than on matrigel. Growth hormone treatment also induced the level of mRNA for insulin-like growth factor I, whereas the amount of mRNA for the male-specific urinary protein alpha 2 mu-globulin was unaffected. Cultures of hepatocytes derived from untreated adult female rats retained high levels of P-450i mRNA but only if the culture medium contained growth hormone. None of the tested treatments with estrogens, androgens, glucocorticoids, or growth hormone induced P-450h mRNA or P-450h immunoreactive protein in cultures of female hepatocytes. We conclude that the somatogenic effects of growth hormone acting alone and directly on the hepatocyte in culture are sufficient to "feminize" the cytochrome P-450 phenotype. The present culture system offers a way to explore the molecular basis for hormonal control of liver gene expression.

Reciprocal regulation of adult rat hepatocyte growth and functional activities in culture by dimethyl sulfoxide

Hepatocyte DNA synthesis, initiated by epidermal growth factor (EGF), is reversibly inhibited by 2% dimethyl sulfoxide (DMSO). At that concentration, both the survival of the cells in culture and the expression of differentiated functions are prolonged. DMSO does not affect thymidine uptake or EGF receptor binding. Moreover, EGF receptor binding is maintained at 84% of initial 12 hr binding when cells are cultured for several days in the presence of DMSO, whereas specific receptor binding declines to 49% of initial binding under standard culture conditions without DMSO. Studies of hepatocyte functional activity indicate that, during early culture, total cellular export protein synthesis, specific albumin synthesis, and glycogen synthesis are enhanced in the presence of DMSO. Dexamethasone is required for the effect of DMSO on survival, and although dexamethasone alone enhances hepatocyte DNA synthesis in the presence of EGF, it does not reverse the inhibitory effect of 2% DMSO on DNA replication. The correlation of prolonged survival with growth inhibition supports the hypothesis that hepatic growth and differentiated functional activity may be reciprocally regulated.

Cellular interactions promote tissue-specific function, biomatrix deposition and junctional communication of primary cultured hepatocytes

Hepatocytes, prepared from normal adult rat liver, were seeded onto a collagen substratum and cultured alone or in the presence of rat liver endothelial cells. When hepatocytes were cultured alone in a hormonally defined serum-free medium, decreased albumin production and rapid morphological deterioration of bile canaliculi structures and gap junctions occurred within 4 to 5 days. In contrast, hepatocytes cocultured with liver mesenchymal cells remained morphologically intact and biochemically functional for at least 4 weeks. They reorganized into small islands, continued to secrete high levels of albumin, did not express alpha-fetoprotein (a fetal marker), and remained strongly dye coupled. All of the hepatocytes synthesized albumin and retained their gap junctional channels. No junctional communication was observed between hepatocytes and endothelial cells. Long fibers containing fibronectin, Type I collagen and laminin distributed over the hepatocytes were induced in coculture but never appeared in hepatocytes cultured alone. Moreover, supplementation of the hormonally defined medium with phenobarbital and dimethyl sulfoxide, both of which improve the life span and functional activities of cultured hepatocytes, failed to induce reticulin fiber formation in pure culture of hepatocytes. The modulation of albumin secretion, biomatrix deposition and junctional communication observed in hepatocytes cultured with sinusoidal liver cells was also obtained when hepatocytes were in association with various epithelial or mesenchymal cells [rat liver epithelial cells (T51B), mouse embryonic fibroblasts (NIH 3T3), human or rat dermal fibroblasts and bovine aorta endothelial cells (AG 4762)].

Primary culture of cryopreserved adult human hepatocytes on homologous extracellular matrix and the influence of monocytic products on albumin synthesis

Cultured human hepatocytes provide a useful method for studies of specific metabolic functions, such as plasma protein synthesis or drug metabolism in man and specific interaction of microorganisms with the human liver cell. In vitro studies using human hepatocytes are seriously hampered by the limited availability of viable tissue and the lack of suitable methods for preservation of hepatocytes. In addition, normal adult human hepatocytes, under classical culture conditions, do not proliferate in vitro. Recently, we have reported a method for long-term storage of human hepatocytes, using a cryopreservation technique. However, after thawing, the efficiency of cell seeding onto tissue culture plastic and, accordingly, the survival of hepatocytes in primary cultures were decreased as compared to freshly prepared and cultured hepatocytes. In the present study, we report the effects of extracellular matrix (ECM) obtained from normal liver of kidney donors on the attachment efficiency, survival, some metabolic functions and fine structure of human hepatocytes. It was found that the deleterious effect of deep-freeze storage on attachment efficiency and survival of hepatocytes could be significantly reduced by using tissue culture plastic precoated with human liver ECM. Hepatocytes survived for more than 4-6 weeks, without evidence of fibroblast overgrowth. Using this in vitro experimental system, we have also shown that these hepatocytes synthesize several liver-specific acute phase proteins, and monocytic products were able to decrease the hepatocytic synthesis of albumin while total protein synthesis remained unchanged. These results support our previous observations in cultured rodent hepatocytes, indicating the important role of monocytic products in the regulation of liver synthesis of albumin in inflammatory diseases in man.

Cell-cell and cell-matrix interactions differentially regulate the expression of hepatic and cytoskeletal genes in primary cultures of rat hepatocytes

Freshly isolated adult rat hepatocytes exhibit a flat, extended morphology when cultured on dried rat tail collagen in the presence of growth factors; they actively synthesize DNA and express high levels of cytoskeletal mRNAs and proteins (actin, tubulin, cytokeratins, vinculin, alpha-actinin, and desmoplakin), while exhibiting low levels of liver-specific mRNAs (albumin, alpha 1-inhibitor III, and alpha 1-antitrypsin) and limited synthesis and secretion of albumin. Hepatocytes cultured on hydrated gel matrix from the Engelbreth-Holm-Swarm (EHS) mouse tumor form small spherical aggregates and exhibit low DNA, cytoskeletal mRNA, and protein synthesis, while at the same time exhibiting elevated liver-specific mRNAs and albumin production; these cells, therefore, more nearly conform to the program of gene expression seen within the normal animal. Hepatocytes on hydrated rat tail collagen resemble those on dry collagen when cultured at low density, but at high density they form compact trabecular aggregates, synthesize negligible amounts of DNA, and maintain a pattern of gene expression resembling that of hepatocytes seeded on the EHS matrix. If cell morphology is compact, as on EHS or on hydrated rat tail collagen when densely populated, DNA synthesis and expression of cytoskeletal genes are low, while liver-specific mRNAs are abundant. When cells are extended the opposite is the case. Without the growth supplement DNA synthesis is low throughout but gene expression is little affected. These studies point to the importance of cell-cell and cell-matrix interactions in determining the differentiated phenotype of hepatocytes, and they reveal an inverse relationship between cytoskeletal and liver-specific protein expression.

Regulation of gene expression in adult rat hepatocytes cultured on a basement membrane matrix

Freshly isolated adult rat hepatocytes, when cultured on type I collagen (commercially available as Vitrogen), assume a polygonal shape, form a stable monolayer within 24 hours, but lose the capacity to express some liver-specific functions over time in culture. We incubated hepatocytes in a serum-free medium on a reconstituted basement membrane gel, "matrigel" (prepared from an extract of extracellular matrix of the murine Engelbreth-Holm-Swarm sarcoma), and observed that the cells adhered firmly, remained rounded as single cells or clusters, and maintained liver-specific gene expression for more than 1 week in vitro. Hepatocytes on matrigel secreted substantially higher amounts of albumin, transferrin, haptoglobin, and hemopexin, Northern blot analyses of extracted cellular RNA, expressed increased amounts of mRNA for the liver-specific protein albumin (as compared with cells on vitrogen). In cultures treated with phenobarbital, cytochrome P-450b, and cytochrome P-450e, mRNAs and proteins were barely detectable in cells on Vitrogen but were induced to levels similar to those in the liver in vivo in matrigel cultures. Likewise, the use of matrigel greatly enhanced the induction of mRNA and protein for P-450c by 3-methylcholanthrene and for P-450p by steroidal and nonsteroidal inducers. However, neither substratum permitted induction of P-450d by 3-methylcholanthrene, suggesting that the effects of matrigel are selective even for expression in liver of members of the superfamily of cytochrome P-450 genes. Within 5 days in cultures on Vitrogen, hepatocytes expressed detectable amounts of fetal liver aldolase activity and also mRNA for vimentin and type I collagen, each considered a phenotypic change reflecting hepatocyte "dedifferentiation." None of these was present in cells on matrigel. Responsiveness to mitogenic stimuli, as judged by incorporation of 3H-thymidine into DNA, was also decreased in hepatocytes cultured on matrigel. Finally, there was a remarkable increase in the levels of both matrices during the first 2 days in culture. However, the continuously cytoskeleton mRNA over time in culture than did the rounded cells on matrigel. We conclude that hepatocytes cultured on matrigel, as opposed to the standard collagen, exhibit remarkably enhanced expression of many liver-specific functions.

Regulation of rat mammary gene expression by extracellular matrix components

In the mammary gland the induction and maintenance of differentiation are dependent on both lactogenic hormones and the extracellular matrix (ECM). Since mammary epithelial cells differentiate on a basement membrane in vivo we have examined the effects of basement membrane components on the expression of milk protein genes in primary rat mammary cultures. We examined the effects of a basement membrane gel derived from the Englebreth-Holm-Swarm tumor as well as its major component, laminin, on the expression of a group of milk protein genes. We demonstrate that the basement membrane gel induces alpha-casein and alpha-lactalbumin (alpha-LA) accumulation up to 160- and 70-fold, respectively, of that on tissue culture plastic. Laminin, a major component of the basement membrane, also caused significant induction of these same proteins. In order to determine whether these ECM effects occurred at a translational or post-translational level, pulse-chase experiments were performed. These experiments demonstrated that a laminin substratum selectively effects milk protein turnover and secretion. In order to demonstrate whether ECM effects occurred at the level of steady state accumulation of mRNA we performed dot blot and Northern analyses using cloned cDNA probes for alpha-, beta-, and gamma-caseins and alpha-LA. These studies demonstrated that ECM components induced alpha- and beta-caseins up to 10-fold, and alpha-LA up to 3-fold, with no significant effect on gamma-casein. These results demonstrate that milk protein genes are not coordinately regulated by ECM components. Furthermore, since the amount of induction of milk proteins exceeds the amount of induction of mRNAs for these proteins, we conclude that in our system a major effect of ECM components is at the translational and/or post-translational levels. Based on these findings we propose a model in which basement membrane components effect mammary gene expression at multiple levels.

Persistence of liver-specific messenger RNA in cultured hepatocytes: different regulatory events for different genes

Normal adult rat hepatocytes plated on rat tail collagen-coated dishes and fed a chemically defined medium supplemented with epidermal growth factor and dimethylsulfoxide (DMSO) were examined over a 40-d culture period for (a) the amount of albumin secreted; (b) steady-state albumin mRNA levels; (c) steady-state mRNA levels for six other liver-specific genes and three common genes; and (d)transcription of several liver-specific and common genes using isolated nuclei. DMSO-treated hepatocytes in culture for 40 d expressed albumin mRNA at 45% the level of normal liver and five other liver-specific genes at levels ranging from 21% to 72% of those in normal liver. The rate of synthesis of ligandin RNA using nuclei from 40-d hepatocytes in a nascent chain extension assay was 130% of the value obtained for normal liver, indicating that liverlike transcriptional activity for ligandin was maintained in this in vitro culture system. In contrast, the rates of synthesis of albumin and phosphoenolpyruvate carboxykinase (PepCK) mRNAs using nuclei from 40-d hepatocytes were 8% and less than 1%, respectively, and, therefore, were at levels that were much lower than was expected given the steady-state mRNA levels for these two genes. The discrepancy between the steady-state mRNA levels and rates of synthesis of RNA was analyzed, and the results suggest that the albumin and PepCK mRNAs from hepatocytes in culture may be more stable than those from liver. A plateau period for secretion of albumin, expression of albumin, alpha 1-antitrypsin, ligandin, phenylalanine hydroxylase, and PepCK mRNAs, and synthesis of albumin RNA using isolated nuclei was observed from days 6 to 40. The usefulness at a biological and molecular level of a hepatocyte culture system in which liver-specific genes are expressed over a long plateau period is discussed.