Isolation of cDNA clones specific for collagen IV and laminin from mouse teratocarcinoma cells

Retinoic acid promotes transcription of the platelet-derived growth factor alpha-receptor gene

Retinoic acid together with dibutyryl cyclic AMP stimulated transcription of the platelet-derived growth factor alpha-receptor gene in embryonal carcinoma cells (line F9). Processed mRNA transcripts appeared within 4 h after exposure to these agents, and functional alpha:alpha homodimers appeared within 24 h.

Multiple isoforms of the mouse retinoic acid receptor alpha are generated by alternative splicing and differential induction by retinoic acid

Together with the previously described mouse retinoic acid receptor alpha-1 (mRAR-alpha 1, formerly mRAR-alpha 0), we have isolated and characterized here a total of seven mRAR-alpha cDNA isoforms (mRAR-alpha 1 to alpha 7). These isoforms are generated from mRAR-alpha primary transcript(s) of a single gene by alternative splicing of at least eight different exons with the exon which encodes the amino acid sequence of their common B region. All of these isoforms differ in their 5'-untranslated regions (5'-UTRs) and, in the case of mRAR-alpha 1 and alpha 2, also in the sequences encoding the N-terminal A region which is known to be important for differential trans-activation by other members of the nuclear receptor superfamily. In addition, the sequences encoding the open reading frames (ORFs) of mRAR-alpha 3 and alpha 4 cDNA isoforms remain open to their very 5' ends, which suggests that these two isoforms may also encode RAR-alpha s with unique A region amino acid sequences. The two predominant isoforms, mRAR-alpha 1 and alpha 2, were found to be differentially expressed in mouse adult and fetal tissues, as well as in P19 and F9 embryonal carcinoma (EC) cell lines. Interestingly, the expression of mRAR-alpha 2, in contrast to that of the mRAR-alpha 1 isoform, was induced by retinoic acid (RA) in EC cells, thus suggesting the presence of two promoters in the 5' region of the mRAR-alpha gene, which differ in their response to RA. The conservation between mouse and human RAR-alpha 1 and alpha 2 cDNA isoform sequences, as seen by cross-hybridization in Southern blots or by DNA sequence analysis, together with their differential patterns of expression, strongly suggests that they perform specific functions during embryogenesis and in the adult.

Characterization of a functional promoter for the human retinoic acid receptor-alpha (hRAR-alpha)

The three retinoic acid receptors RAR-alpha, beta and gamma are thought to mediate the effects of RA in vivo. We have determined here the exon organisation in the 5' region of the human RAR-alpha (hRAR-alpha) gene, and have identified its promoter. This promoter drives the expression of promoterless beta-globin or CAT reporter genes when transfected into HeLa, Cos-1 or mouse embryonal carcinoma (EC) P19.6 cells in culture. There are no TATA or CCAAT-box elements in this promoter, which appears to belong to the class of promoters made up of an initiator element preceded by several putative binding sites for the transcription factor Sp1. In addition, the hRAR-alpha promoter region contains a number of sequences that are similar to known enhancer elements. Notably, the hRAR-alpha promoter contains a sequence identical to a binding site for the Krox-20 transcription factors, a zinc finger-containing protein which is thought to play a role in the early development of the mouse central nervous system.

Retinoic acid promotes transcription of the platelet-derived growth factor alpha-receptor gene

Retinoic acid together with dibutyryl cyclic AMP stimulated transcription of the platelet-derived growth factor alpha-receptor gene in embryonal carcinoma cells (line F9). Processed mRNA transcripts appeared within 4 h after exposure to these agents, and functional alpha:alpha homodimers appeared within 24 h.

Adenovirus 12S E1A gene represses differentiation of F9 teratocarcinoma cells

The F9 teratocarcinoma cell line differentiates in vitro after treatment with retinoic acid and cAMP and has been a widely used model system for the study of the molecular events that are responsible for cellular commitment and differentiation during early development. Previous experiments have suggested intriguing parallels between the control of gene expression during F9 cell differentiation and the regulation of gene expression by adenovirus E1A. Transfection of a 12S E1A-expressing plasmid into terminally differentiated, nonproliferating F9 cells generates, at high frequency, colonies of dividing cells, each of which expresses E1A. Cell lines established from these colonies proliferate in the presence of retinoic acid and have lost the fully differentiated phenotype as characterized by the absence of expression of a series of differentiation-specific genes. We conclude that expression of the viral 12S E1A gene product interferes with retinoic acid-induced F9 cell differentiation. Moreover, the results suggest that the differentiation process, as defined by markers of terminal differentiation, may not be a permanent event but can be reversed by E1A expression.

Regulation of fibrillar collagen types I and III and basement membrane type IV collagen gene expression in pressure overloaded rat myocardium

Left ventricular hypertrophy is based on cardiac myocyte growth. The hypertrophic process can be considered heterogeneous based on whether it also includes a remodeling and accumulation of fibrillar types I and III collagens that are responsible for impaired myocardial stiffness. In the heart, the messenger RNA (mRNA) for fibrillar collagen types I and III has been detected only in cardiac fibroblasts, whereas mRNA for basement membrane collagen type IV is present in both fibroblasts and myocytes. We studied the early and long-term expression of these collagenous proteins in rat myocardium after abdominal aortic banding with renal ischemia. Complementary DNA probes for rat pro-alpha 2 (I), mouse type III and mouse type IV collagens, and chicken beta-actin were used. Northern and dot blot analysis on total RNA extracted from left ventricular tissue indicated a sixfold increase in steady-state levels of mRNA for collagen type I on day 3 of abdominal aortic banding, which had declined to control levels by day 7 where it remained rather constant at 4 and 8 weeks. Type III collagen showed a similar pattern of gene expression after banding. mRNA levels for type IV collagen, on the other hand, were elevated on day 1 after banding, returning to control at day 7 and remaining constant. Actin mRNA levels also increased on day 1 of banding, followed by a rapid return to control levels. Monospecific antibody to types I and III collagens and immunofluorescent light microscopy on frozen sections of the myocardium revealed that at 1 week after banding, the distribution and density of these collagens were similar to those of control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasminogen activator inhibitor type-2 is a major protein induced in human fibroblasts and SK-MEL-109 melanoma cells by tumor necrosis factor

Tumor necrosis factor (TNF) induces the synthesis of two proteins of Mr 42 and 36 kDa in human fibroblasts and SK-MEL-109 melanoma cells. To identify these proteins, a lambda gt10 cDNA library was prepared from the mRNA of TNF-treated SK-MEL-109 cells. By screening this library, we found a cDNA that preferentially hybridized to TNF-induced RNA. Hybrid-selected mRNA was translated into a protein of 42 kDa; cDNA sequence analysis followed by a comparison with other known protein sequences identified this protein with plasminogen activator inhibitor, type-2 (PAI-2). After removal of TNF, PAI-2 mRNA turned over rapidly, with an apparent half-life of approximately 2.5 h. Addition of dexamethasone increased the turnover of this mRNA, suggesting that the level of PAI-2 mRNA could be regulated post-transcriptionally by glucocorticoids. PAI-2 was not secreted, but accumulated in fibroblasts continuously treated with TNF.

Gene expression in visceral endoderm: a comparison of mutant and wild-type F9 embryonal carcinoma cell differentiation

We have examined the abundance and cell specificity of several mRNAs that are regulated during the retinoic acid (RA)-induced differentiation of F9 embryonal carcinoma cells to visceral endoderm. The experiments confirmed the multistep nature of this process by demonstrating the expression of the ERA-1/Hox 1.6 message within 6 h after RA addition; the expression of messages specific for the extracellular matrix proteins laminin B1 and B2, and collagen IV(alpha 1) between days 4 and 12; and the expression of two visceral endoderm markers, alpha-fetoprotein (AFP) and H19, by days 8-15. In situ hybridization experiments revealed that the collagen IV(alpha 1) mRNA is restricted to the outer cell layer of F9 cell aggregates regardless of the presence or absence of RA. Laminin B1 and B2 mRNAs are concentrated in the outer cell layer of RA-treated aggregates although significant levels of message are also observed within the interior cells of the aggregates. Unexpectedly, AFP mRNA is detectable in only a subset of the outer cells of F9 cell aggregates grown 15 d in the presence of RA. The results obtained from wild-type F9 cells were compared with those from a mutant F9 cell line, RA-5-1, which was previously shown to synthesize collagen IV containing six- to ninefold less 4-hydroxyproline than that in wild-type F9 cells. RA-5-1 cells exhibit four- to sixfold less of the mRNAs encoding two visceral endoderm proteins, AFP and H19, than wild-type F9 cells after RA treatment of RA-5-1 aggregates. RA-5-1 cells, however, do exhibit an RA-associated increase in the level of ERA-1/Hox 1.6 mRNA within 6 h after adding RA. Although the collagen IV protein level is similar in wild-type F9 and RA-5-1 aggregates, the collagen IV(alpha 1) message level is 6-20-fold greater in aggregates of mutant cells than in aggregates of wild-type cells. Moreover, in situ hybridizations showed that this message is evenly distributed throughout the RA-5-1 aggregates rather than restricted to the outer cell layers as it is in wild-type F9 aggregates. These results suggest that abnormal collagen IV expression and localization are associated with decreased expression of the visceral endoderm markers, AFP and H19, in RA-5-1 cell aggregates.

Cyclic AMP analogs and retinoic acid influence the expression of retinoic acid receptor alpha, beta, and gamma mRNAs in F9 teratocarcinoma cells

Retinoic acid (RA) receptor alpha (RAR alpha) and RAR gamma steady-state mRNA levels remained relatively constant over time after the addition of RA to F9 teratocarcinoma stem cells. In contrast, the steady-state RAR beta mRNA level started to increase within 12 h after the addition of RA and reached a 20-fold-higher level by 48 h. This RA-associated RAR beta mRNA increase was not prevented by protein synthesis inhibitors but was prevented by the addition of cyclic AMP analogs. In the presence of RA, cyclic AMP analogs also greatly reduced the RAR alpha and RAR gamma mRNA levels, even though cyclic AMP analogs alone did not alter these mRNA levels. The addition of either RA or RA plus cyclic AMP analogs did not result in changes in the three RAR mRNA half-lives. These results suggest that agents which elevate the internal cyclic AMP concentration may also affect the cellular response to RA by altering the expression of the RARs.

Expression of REX-1, a gene containing zinc finger motifs, is rapidly reduced by retinoic acid in F9 teratocarcinoma cells

In the presence of retinoic acid (RA), cultured F9 murine teratocarcinoma stem cells differentiate into nontumorigenic cells resembling the extraembryonic endoderm of the early mouse embryo. By differential hybridization screening of an F9 cell cDNA library, we isolated a 1,745-nucleotide cDNA for a gene, REX-1 (for reduced expression), whose steady-state mRNA level began to decline in F9 cells in monolayer culture within 12 h after the addition of RA. By 48 to 96 h after RA treatment of F9 cells in monolayer culture, the REX-1 steady-state mRNA level was more than sevenfold lower than the level in undifferentiated F9 stem cells. The REX-1 mRNA decrease did not result from the reduction in cell growth rate associated with the differentiation process, since the REX-1 mRNA level did not decline in F9 cells that were partially growth arrested after 48 h of isoleucine deprivation. The RA-associated REX-1 mRNA decrease resulted primarily from a reduction in the transcription rate of the REX-1 gene in the presence of RA. In contrast to results in F9 cells, we have been unable thus far to detect REX-1 mRNA in day 7.5 to 12.5 mouse embryo RNA samples or in the P19 teratocarcinoma stem cell line. The putative REX-1 protein identified by DNA sequence analysis contains four repeats of the zinc finger nucleic acid-binding motif and a potential acidic activator domain, suggesting that REX-1 encodes a regulatory protein. The REX-1 gene is not identical to the previously reported murine genes that encode zinc finger-containing proteins.

Cyclic AMP analogs and retinoic acid influence the expression of retinoic acid receptor alpha, beta, and gamma mRNAs in F9 teratocarcinoma cells

Retinoic acid (RA) receptor alpha (RAR alpha) and RAR gamma steady-state mRNA levels remained relatively constant over time after the addition of RA to F9 teratocarcinoma stem cells. In contrast, the steady-state RAR beta mRNA level started to increase within 12 h after the addition of RA and reached a 20-fold-higher level by 48 h. This RA-associated RAR beta mRNA increase was not prevented by protein synthesis inhibitors but was prevented by the addition of cyclic AMP analogs. In the presence of RA, cyclic AMP analogs also greatly reduced the RAR alpha and RAR gamma mRNA levels, even though cyclic AMP analogs alone did not alter these mRNA levels. The addition of either RA or RA plus cyclic AMP analogs did not result in changes in the three RAR mRNA half-lives. These results suggest that agents which elevate the internal cyclic AMP concentration may also affect the cellular response to RA by altering the expression of the RARs.

Ito-cell gene expression and collagen regulation

Ito cells are perisinusoidal cells thought to be a major source of collagen in normal and fibrotic livers. These cells appear to have features similar to several cell types but when cultured assume a fibroblast-like morphology. In this study we evaluated the phenotype of both freshly isolated and cultured Ito cells by examining their gene expression. To better define the modulators of Ito-cell collagen synthesis, we also examined the effect of transforming growth factor-beta 1, tumor necrosis factor-alpha and dexamethasone on collagen synthesis by these cells. Northern hybridization analysis revealed that cultured Ito cells expressed different types of procollagen mRNAs than did freshly isolated cells. Cultured cells contained large amounts of type I procollagen mRNA and lesser amounts of types III and IV, whereas freshly isolated cells contained more type IV procollagen mRNA than types I and III. Treatment of cultured cells with either transforming growth factor-beta 1 or tumor necrosis factor-alpha resulted in a greater than three-fold increase in total collagen content, and the effects of these cytokines on Ito-cell collagen synthesis involved different levels of gene regulation. Transforming growth factor-beta 1-treated cells had an approximately threefold increase in their type I procollagen mRNA levels, whereas no increase in this mRNA level was found in tumor necrosis factor-alpha-treated cells. Transforming growth factor-beta 1 treatment induced a twofold increase in transforming growth factor-beta 1 mRNA content in cultured cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of REX-1, a gene containing zinc finger motifs, is rapidly reduced by retinoic acid in F9 teratocarcinoma cells

In the presence of retinoic acid (RA), cultured F9 murine teratocarcinoma stem cells differentiate into nontumorigenic cells resembling the extraembryonic endoderm of the early mouse embryo. By differential hybridization screening of an F9 cell cDNA library, we isolated a 1,745-nucleotide cDNA for a gene, REX-1 (for reduced expression), whose steady-state mRNA level began to decline in F9 cells in monolayer culture within 12 h after the addition of RA. By 48 to 96 h after RA treatment of F9 cells in monolayer culture, the REX-1 steady-state mRNA level was more than sevenfold lower than the level in undifferentiated F9 stem cells. The REX-1 mRNA decrease did not result from the reduction in cell growth rate associated with the differentiation process, since the REX-1 mRNA level did not decline in F9 cells that were partially growth arrested after 48 h of isoleucine deprivation. The RA-associated REX-1 mRNA decrease resulted primarily from a reduction in the transcription rate of the REX-1 gene in the presence of RA. In contrast to results in F9 cells, we have been unable thus far to detect REX-1 mRNA in day 7.5 to 12.5 mouse embryo RNA samples or in the P19 teratocarcinoma stem cell line. The putative REX-1 protein identified by DNA sequence analysis contains four repeats of the zinc finger nucleic acid-binding motif and a potential acidic activator domain, suggesting that REX-1 encodes a regulatory protein. The REX-1 gene is not identical to the previously reported murine genes that encode zinc finger-containing proteins.

A retinoic acid-responsive element is present in the 5' flanking region of the laminin B1 gene

The retinoic acid (RA)-associated differentiation of murine F9 teratocarcinoma stem cells results in dramatic changes in gene expression. The cellular gene encoding the B1 subunit of the extracellular matrix protein laminin is transcriptionally activated by RA, and its transcription is further enhanced by N6,O2'-dibutyryladenosine 3',5'-cyclic monophosphate (Bt2cAMP) during the differentiation of F9 stem cells into extraembryonic parietal endoderm cells. We now report that expression vectors encoding the human RA receptors RAR-alpha, RAR-beta, and RAR-gamma can activate chloramphenicol acetyltransferase (CAT) expression from laminin B1 promoter/CAT expression vectors (e.g., p1.6LAMCAT) in RA-treated F9 cells, as measured in a transient transfection assay. Bt2cAMP does not further enhance the RA-associated increase in CAT activity. Through the use of deletion and mutation analyses, the RA-responsive element (RARE) of the murine laminin B1 gene has been defined as a 46-base-pair element between -477 and -432 of the laminin B1 5' flanking region. Insertion of a region of DNA containing this RARE in either orientation into a thymidine kinase promoter/CAT expression vector causes CAT expression to be activated 5- to 9-fold by the cotransfected human RAR-alpha or RAR-beta constructs in RA-treated F9 cells, and this RARE also functions in human HeLa cells. In contrast, this RARE in the p1.6LAMCAT vector does not activate CAT expression when cotransfected into F9 stem cells with the c-erbA gene in the presence of thyroid hormone. This suggests that the laminin B1 gene is activated by RA but not by thyroid hormone in vivo.

Control of beta-interferon expression in murine embryonal carcinoma F9 cells

Murine embryonal carcinoma F9 cells, a tissue culture model for early embryonic development, do not produce interferon (IFN) in response to poly(I-C), as determined by an antiviral assay. RNase protection analyses were used to examine total RNA extracted from the cells for the presence of beta-IFN RNA. Whereas F9 cells differentiated in vitro with retinoic acid produced a biologically active protein as well as beta-IFN RNA in response to poly(I-C), undifferentiated F9 cells produced no detectable beta-IFN RNA even in the presence of cycloheximide, an IFN-superinducing agent. These results show that undifferentiated embryonal carcinoma cells do not accumulate beta-IFN RNA in response to an IFN-inducing agent, suggesting a transcriptional regulatory mechanism. However, this control mechanism is altered upon differentiation, since the gene can be transcriptionally activated in retinoic acid-differentiated cells.

Increased proteoglycan synthesis following the differentiation of F9 embryonal carcinoma cells: formation of a differentiation-specific proteoheparan sulfate

We have examined changes in proteoglycan synthesis by F9 embryonal carcinoma cells after the cells have been treated with retinoic acid or retinoic acid plus cholera toxin. Retinoic acid is known to stimulate the differentiation of this cell type to a primitive endoderm-like cell characterized by the production of basement membrane components such as type IV collagen, laminin and proteoglycans. We have now demonstrated that proteoglycan synthesis and secretion were further stimulated when cholera toxin was added in addition to retinoic acid. Moreover, media of these fully differentiated cells was found to contain a different species of proteoheparan sulfate not produced by stem cells or retinoic acid-treated cells. This proteoheparan sulfate had a high density upon CsCl gradient centrifugation. The protein core of this proteoheparan sulfate was estimated by SDS gel electrophoresis to be approximately 15,000 daltons.

Retinoic acid receptor expression vector inhibits differentiation of F9 embryonal carcinoma cells

Expression vectors have been constructed for a region of the human retinoic acid receptor-alpha (hRAR-alpha) and transferred into F9 embryonal carcinoma (EC) cells. When the vectors are overexpressed in F9 cells, clones can be selected for resistance to retinoic acid-induced differentiation. This effect is obtained even when the hRAR-alpha region is expressed as a beta-galactosidase fusion protein. Using the beta-galactosidase component of the fusion protein as a marker, overexpression of the fusion protein has been correlated with the retinoic acid-resistance effect. The clones resistant to retinoic acid no longer exhibit the normal retinoic acid induction of endo B cytokeratin, laminin B-1, and tissue plasminogen activator mRNAs observed with normal F9 cells. Retinoic acid induction of type IV alpha-1 collagen and Hox-1.3 RNAs is observed with these clones. When transfected with a thyroid receptor DNA-binding sequence (TRE)/thymidine kinase promoter/luciferase construct, the retinoic acid-resistant clones do not yield the same retinoic acid-induced level of luciferase obtained with F9 cells. It is hypothesized that the RAR vectors are interfering with endogenous RAR(s) in a dominant-negative manner to inhibit retinoic acid-induced differentiation of F9 EC cells.

Adenovirus E1A-mediated negative control of genes activated during F9 differentiation

The phenotype of a differentiated cell results from the expression of a unique set of genes in that cell. The differentiation of F9 teratocarcinoma cells in response to retinoic acid and cyclic AMP is an excellent example of this process, as the appearance of several gene products during the course of the differentiation process has been documented. In principle, the activation of gene expression could be due to the appearance of positive-acting factors, the loss of negative-acting factors, or a combination of both. Since F9 cells have been shown to express a cellular E1A analog whereas differentiated F9 cells do not, and it is known that the viral E1A gene exerts a negative effect on transcription of both viral and cellular genes, we determined whether the cellular genes activated during F9 cell differentiation are subject to E1A negative control. We found that infection of differentiated F9 cells with wild-type adenovirus resulted in a decline in the levels of collagen type IV mRNA and plasminogen activator mRNA, both of which are induced by differentiation. At least for the collagen gene, this phenomenon appears to involve a transcriptional repression.

Control of beta-interferon expression in murine embryonal carcinoma F9 cells

Murine embryonal carcinoma F9 cells, a tissue culture model for early embryonic development, do not produce interferon (IFN) in response to poly(I-C), as determined by an antiviral assay. RNase protection analyses were used to examine total RNA extracted from the cells for the presence of beta-IFN RNA. Whereas F9 cells differentiated in vitro with retinoic acid produced a biologically active protein as well as beta-IFN RNA in response to poly(I-C), undifferentiated F9 cells produced no detectable beta-IFN RNA even in the presence of cycloheximide, an IFN-superinducing agent. These results show that undifferentiated embryonal carcinoma cells do not accumulate beta-IFN RNA in response to an IFN-inducing agent, suggesting a transcriptional regulatory mechanism. However, this control mechanism is altered upon differentiation, since the gene can be transcriptionally activated in retinoic acid-differentiated cells.

Expression of the fibronectin gene

Fibronectin (FN) is an extracellular matrix protein that acts as a substrate for cell migration and adhesion during development. FN adheres to cells through a dimeric membrane protein, the FN receptor. Antibodies to FN and synthetic peptides that inhibit FN-receptor interaction inhibit gastrulation, block neural crest cell migration, arrest cardiac development, and block the fusion of myoblasts to form myotubes. FN and its receptor also appear to be important for lung development, where their expression coincides with the onset of branching morphogenesis, but drops to barely detectable levels in adult lung, indicating developmental specificity. FN expression is generally low in most adult tissues. However, synthesis is drastically increased during injury and wound healing, a process that in many ways mimics development. FN synthesis is also drastically increased in fibroproliferative lung lesions associated with major architectural changes in the lung. Expression of FN is regulated by a variety of growth factors and hormones. Several of these inducers (cAMP, transforming growth factor-beta, epidermal growth factor, platelet-derived growth factor, glucocorticoids, and vitamin D3) have themselves been implicated in developmental processes, and both cAMP and transforming growth factor-beta are known to stimulate expression of other matrix genes. One role of these hormones and growth factors in development may be to control expression of matrix genes, thereby controlling cell migration and adhesion. In the following report, the effect of hormones and growth factors on expression of the FN gene is reviewed.

Adenovirus E1A-mediated negative control of genes activated during F9 differentiation

The phenotype of a differentiated cell results from the expression of a unique set of genes in that cell. The differentiation of F9 teratocarcinoma cells in response to retinoic acid and cyclic AMP is an excellent example of this process, as the appearance of several gene products during the course of the differentiation process has been documented. In principle, the activation of gene expression could be due to the appearance of positive-acting factors, the loss of negative-acting factors, or a combination of both. Since F9 cells have been shown to express a cellular E1A analog whereas differentiated F9 cells do not, and it is known that the viral E1A gene exerts a negative effect on transcription of both viral and cellular genes, we determined whether the cellular genes activated during F9 cell differentiation are subject to E1A negative control. We found that infection of differentiated F9 cells with wild-type adenovirus resulted in a decline in the levels of collagen type IV mRNA and plasminogen activator mRNA, both of which are induced by differentiation. At least for the collagen gene, this phenomenon appears to involve a transcriptional repression.

Early retinoic acid-induced F9 teratocarcinoma stem cell gene ERA-1: alternate splicing creates transcripts for a homeobox-containing protein and one lacking the homeobox

Retinoic acid (RA), the natural acidic derivative of vitamin A, can modulate the expression of specific genes and can induce some cell types, such as the murine F9 teratocarcinoma stem cell line, to differentiate in culture. As an initial step toward understanding the molecular mechanism(s) by which RA exerts these effects, we previously isolated cDNA clones for a gene, ERA-1, which has the characteristics of an early, direct target for RA. We demonstrated that RA causes a rapid, dose-dependent, and protein synthesis-independent expression of the ERA-1 gene (G. J. LaRosa and L. J. Gudas, Proc. Natl. Acad. Sci. USA 85:329-333, 1988). We now report the full-length cDNA sequence and the further characterization of this gene. The data indicate that the RA-induced 2.2- to 2.4-kilobase ERA-1 RNA species that we previously detected consists of two alternately spliced messages. One mRNA encodes a protein with a predicted mass of about 36 kilodaltons (kDa) that possesses the Hox 1.6 homeobox domain. The other mRNA encodes a truncated protein of about 15 kDa which is identical to the 36-kDa protein for 114 amino acids at the amino-terminal end but which lacks the homeobox amino acid sequence. The RA-associated increase in the ERA-1 mRNA level does not appear to be due to message stabilization, suggesting that the response is at the level of transcription. By Northern (RNA) blot analysis, the usual 2.2- to 2.4-kilobase mRNA species was also rapidly expressed in P19 teratocarcinoma cells during their differentiation to fibroblastic cells in response to RA and was detected in day 10.5 and day 13.5 mouse embryos. This result indicates that the expression of this gene is not limited to the endodermal differentiation of F9 cells.

Molecular biology of keratinocyte differentiation

Epidermal keratinocytes (skin cells) are highly specialized epithelial cells designed to perform a very specific function, separation of the organism from its environment. To accomplish this the cells synthesize precursors and assemble them into two distinct structures, the cornified envelope and keratin intermediate filaments. The intermediate filaments are assembled from keratin monomers and the cornified envelope is assembled from a protein called involucrin and several other proteins. Expression of involucrin and the keratins genes are regulated as a function of the stage of keratinocyte differentiation and by various external agents such as calcium and vitamin A. To study the function of these structures and the regulation of precursor production we have cloned cDNA and genomic clones encoding involucrin and four of the keratin polypeptides. Retinoids profoundly alter the differentiation pattern of human epidermal keratinocytes, but the underlying biochemical basis of this change is not known. In this report we describe retinoid-promoted changes in keratin gene expression that may, in part, be responsible for the alteration in cellular phenotype in the presence of the vitamin. We also describe the novel structure of the human 40 kD keratin, a member of the keratin family that is retinoid responsive and is likely to be important during epidermal development. Finally, we describe the structure of the envelope precursor protein, involucrin, as determined from its DNA sequence and speculate on its role in cornified envelope formation.

An embryonic DNA-binding protein specific for a region of the human IFN beta 1 promoter

Embryonal carcinoma (EC) cells are unable to make interferon in response to inducing agents. This block disappears after differentiation. We have found that nuclear extracts from undifferentiated P19 EC cells contain a DNA-binding activity which specifically recognizes a region within the human interferon-beta 1 promoter. This activity is absent from differentiated cell types, both of EC and non-EC origin. The binding of the factor in undifferentiated EC cells leads to dramatic changes in the overall protein binding pattern of the interferon promoter as compared with differentiated cells, and may be responsible for repression of the endogenous interferon-beta gene prior to differentiation.

Undifferentiated F9 embryonal carcinoma cells produce a short-chain collagen molecule

The undifferentiated F9 embryonal carcinoma cells produce a unique collagen that decreases in amount during retinoic acid-induced differentiation of F9 cells into basement-membrane parietal endoderm. A bacterial-collagenase-sensitive protein of approx. 60,000 Da was resolved on polyacrylamide-gel electrophoresis. After pepsin digestion, two pepsin-resistant fragments containing hydroxyproline were demonstrated, suggesting that a portion of the molecule has a stable triple helix. The mRNA from the undifferentiated F9 cells translates a collagenase-sensitive protein with a molecular mass consistent with the 60,000 Da collagenous protein produced by undifferentiated F8 cells.

Early retinoic acid-induced F9 teratocarcinoma stem cell gene ERA-1: alternate splicing creates transcripts for a homeobox-containing protein and one lacking the homeobox

Retinoic acid (RA), the natural acidic derivative of vitamin A, can modulate the expression of specific genes and can induce some cell types, such as the murine F9 teratocarcinoma stem cell line, to differentiate in culture. As an initial step toward understanding the molecular mechanism(s) by which RA exerts these effects, we previously isolated cDNA clones for a gene, ERA-1, which has the characteristics of an early, direct target for RA. We demonstrated that RA causes a rapid, dose-dependent, and protein synthesis-independent expression of the ERA-1 gene (G. J. LaRosa and L. J. Gudas, Proc. Natl. Acad. Sci. USA 85:329-333, 1988). We now report the full-length cDNA sequence and the further characterization of this gene. The data indicate that the RA-induced 2.2- to 2.4-kilobase ERA-1 RNA species that we previously detected consists of two alternately spliced messages. One mRNA encodes a protein with a predicted mass of about 36 kilodaltons (kDa) that possesses the Hox 1.6 homeobox domain. The other mRNA encodes a truncated protein of about 15 kDa which is identical to the 36-kDa protein for 114 amino acids at the amino-terminal end but which lacks the homeobox amino acid sequence. The RA-associated increase in the ERA-1 mRNA level does not appear to be due to message stabilization, suggesting that the response is at the level of transcription. By Northern (RNA) blot analysis, the usual 2.2- to 2.4-kilobase mRNA species was also rapidly expressed in P19 teratocarcinoma cells during their differentiation to fibroblastic cells in response to RA and was detected in day 10.5 and day 13.5 mouse embryos. This result indicates that the expression of this gene is not limited to the endodermal differentiation of F9 cells.

Protein synthesis inhibitors prevent the induction of laminin B1, collagen IV (alpha 1), and other differentiation-specific mRNAs by retinoic acid in F9 teratocarcinoma cells

Several differentiation-specific genes, including those for collagen IV and laminin, are induced by retinoic acid (RA) in mouse F9 teratocarcinoma cells. Dibutyryl cAMP can enhance the effect of RA in these cells, but dibutyryl cAMP alone does not induce these genes. Inhibition of RNA synthesis with 5-6-dichloro-1-B-D-ribofuranosylbenzimidazole prevents the induction of these genes by RA; inhibition of DNA synthesis with aphidicolin does not prevent the induction. In vitro transcription studies (Wang et al., Dev. Biol., 107:75-86, 1985) demonstrate that these differentiation-specific genes are regulated by RA at least partially at the level of transcription. To determine whether the regulation of transcription of these differentiation-specific genes is a primary effect of RA, we measured the sensitivity of the induction of mRNAs specific for these RA-inducible genes to inhibitors of protein synthesis. RNA was isolated from F9 cells that had been treated for 20 hr with RA (with or without dibutyryl cAMP) in the presence or absence of either cycloheximide or puromycin. We then hybridized the 32P-labeled recombinant plasmids collagen IV (alpha 1) (pcI5), laminin B1 (pcI56), and pcJ6 to RNA from the treated cells. Both cycloheximide and puromycin inhibited the RA induction of the collagen IV (alpha 1), laminin B1, and J6 mRNAs. In contrast, in a control experiment, a 20-hr treatment with cycloheximide did not inhibit the accumulation of metallothionein I-specific mRNA in response to zinc in F9 cells. Thus protein synthesis is required for the expression of the collagen IV (alpha 1), laminin B1, and J6 genes, and this result suggests that the transcriptional regulation of these genes by RA is indirect.

Laminin biosynthesis in the extracellular matrix-producing cell line PFHR9 studied with monoclonal and polyclonal antibodies

The biosynthesis of the basement-membrane glycoprotein laminin in the mouse teratocarcinoma cell line PFHR9 was studied by immunoelectron microscopy and pulse-chase experiments using monoclonal and polyclonal antibodies. By immunoelectron microscopy, most of the protein was found to be aggregated on the outer cell surface. Cytoplasmic stainings were rare and were located next to the intracellular side of the plasma membrane. Sequential immunoprecipitations of cell extracts with a monoclonal antibody (4C12) sensitive to the laminin native conformation and with a polyclonal antibody enables laminin, the B1 subunit and a 410 kDa molecule to be distinguished. Most of the laminin is of the A(B1B2) type, and the 410 kDa molecule appears to be a B1B2 heterodimer. The assembly of laminin from subunits is completed in less than 1 h, and B chains are incorporated via the formation of the B heterodimers. The B2 and A chains are not found as free forms, so their levels appear to be the rate-limiting factors for the assembly of the dimers and laminin respectively. The formation of an uncross-linked A(B1B2) complex as a short-lived intermediate in the biosynthetic process is possible. Together with immunoelectron microscopy, the present study suggests that the protein is rapidly exported after assembly to accumulate on the outer side of the cell membrane. The biosynthesis of laminin in the PFHR9 cell line appears to be similar to that in other matrix-producing cell lines.

Expression of SPARC/osteonectin transcript in murine embryos and gonads

A cDNA clone, p2-4, was isolated from mouse teratocarcinoma-derived parietal endoderm-like cells and used to analyze expression of the corresponding transcript during mouse embryogenesis. Nucleotide-sequence analysis revealed extensive homology between this clone and SPARC/osteonectin cDNA cloned from mouse parietal endoderm and bovine bone cells. The SPARC/osteonectin transcript became more abundant when embryonal carcinoma (EC) cells differentiated into parietal endoderm-like cells. In embryos, the transcript began to appear in the embryo proper on day 11 and continued to be expressed throughout the gestation period. The transcript was also present in extraembryonic membranes and placenta from days 9 and 11 onward, respectively. Thus, expression of the transcript was regulated during differentiation of EC cells and during embryogenesis. In adult mice, several non-bone tissues, including testis, also expressed the transcript. Analysis of germ-cell-deficient mice indicated that non-germ-cell components of the testis expressed the transcript. Analysis of mouse testicular cell lines further suggested that the transcript was abundant in Sertoli cells and Leydig cells. Cumulus oophorus cells that envelope the ovulated egg also expressed high levels of the transcript.

An early effect of retinoic acid: cloning of an mRNA (Era-1) exhibiting rapid and protein synthesis-independent induction during teratocarcinoma stem cell differentiation

Vitamin A and its derivatives (retinoids) exhibit profound effects on the proliferation and differentiation of many cell types. However, the molecular mechanism by which retinoids exert these effects is unknown. Cultured murine F9 teratocarcinoma stem cells, which differentiate into nontumorigenic endoderm cells in response to retinoic acid (RA), have been used to identify genes regulated by RA. A cDNA library synthesized from F9 cells treated with RA for 8 hr has been screened with a cDNA probe enriched for sequences rapidly induced by RA, and a gene that exhibits the characteristics of a primary target for RA has been identified. This gene, early retinoic acid-1 (Era-1), encodes a 2.2- to 2.4-kilobase polyadenylylated RNA; the level of Era-1 mRNA rapidly and transiently increases up to 35-fold, depending on the concentration of exogenous RA. The increase in Era-1 mRNA is dependent on the continuous presence of exogenous RA. The RA-associated increase in Era-1 mRNA is seen even in the presence of protein synthesis inhibitors, but the increase is prevented by inhibitors of RNA synthesis such as actinomycin D. This increase in the steady-state level of Era-1 mRNA in F9 cells is a very early effect of retinoic acid on gene expression in this differentiation system.

Differential control of mRNA levels for Thy-1 antigen and laminin in rat mammary epithelial and myoepithelial-like cells

Thy-1 antigen and laminin are two components often associated with the basement membrane of the rat mammary gland and are thought to be synthesized, at least in part, by the adjacent myoepithelial cells in vivo. The relative levels of Thy-1 mRNA and laminin mRNA are compared in a rat mammary cuboidal epithelial cell line and a derivative elongated myoepithelial-like cell line by hybridizing cloned cDNAs to cellular mRNA isolated from these cell types. Although the elongated myoepithelial-like cells synthesize four times as much laminin protein as the cuboidal epithelial cells, there is only a 1.7-fold increase in laminin mRNA between the two cell types. In contrast the 17-fold increase in Thy-1 antigen between the elongated cells and the cuboidal cells can be accounted for completely by a 14-18-fold increase in Thy-1 mRNA, suggesting that changes in the steady-state levels of Thy-1 mRNA in these cell lines are modulated at either a transcriptional or a post-transcriptional level. Run-off transcription by nuclei isolated from the cell lines does not distinguish between these two possibilities. The comparative results on Thy-1 antigen and laminin show that the enhanced production of two proteins often associated with the basement membrane of the rat mammary gland can be controlled at different levels in the elongated myoepithelial-like cells.

Transcriptional and posttranscriptional effects of dexamethasone on albumin and procollagen messenger RNAs in murine schistosomiasis

We have previously shown that dexamethasone increases albumin mRNA and decreases procollagen steady-state mRNA levels in rat hepatocyte cultures. These studies were extended by evaluating an in vivo model of fibrogenesis (murine schistosomiasis) and by determining a more precise level of gene expression responsible for these changes. Control mice and litter mates infected with Schistosomiasis mansoni were evaluated at 8 weeks postinfection when the livers of the infected mice had become fibrotic and their serum albumin levels significantly decreased. The addition of 4 micrograms/mL dexamethasone to the drinking water of half of the infected mice led to a 75% decrease in the liver collagen content as determined by high-performance liquid chromatography. RNA was extracted from the livers of mice under three conditions: control and infected +/- dexamethasone. This RNA was then hybridized with cDNA probes to determine steady-state levels of specific mRNAs. In the infected mice, albumin mRNA levels were decreased compared to control; however, infected mice treated with dexamethasone increased their albumin mRNA content by 3-fold at 8 weeks. Types I and IV procollagen steady-state mRNA levels in infected mice were increased compared to control while dexamethasone suppressed the mRNA level of collagen in infected mice by 50%. The level of gene expression responsible for these steady-state changes was evaluated by nuclear run-on analysis. While the effect of schistosomiasis on these genes was primarily at a transcriptional level, dexamethasone exerted its effect on different genes in the injured liver by diverse mechanisms, i.e., decreasing collagen synthesis at a transcriptional level and increasing albumin by posttranscriptional mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Carboxyl-terminal sequence of entactin deduced from a cDNA clone

Entactin is a widely distributed basement membrane sulfated glycoprotein of approximately equal to 150 kDa. The entactin gene is expressed early in mouse embryogenesis. Two cDNA clones complementary to rat entactin mRNA were isolated by antibody screening of an oligo(dT)-primed cDNA library constructed in the lambda gt11 expression vector. One of the clones, lambda 1E, was subcloned into plasmid pBR322 and further characterized. The clone contained sequences complementary to an mRNA species 6 kilobases in length. This mRNA was translated in rabbit reticulocyte lysates to yield a polypeptide of 143 kDa that was precipitated with anti-entactin antiserum. The cDNA insert, 1328 base pairs long, was sequenced and found to contain an open reading frame of 729 base pairs that coded for 243 amino acids at the carboxyl terminus of entactin. Analysis of the peptide revealed no extended alpha-helical or beta-sheet secondary structures. Radiolabeled probes prepared by nicktranslation of p lambda 1E were used to monitor the steady-state levels of entactin mRNA in F9 embryonal carcinoma cells that were induced to differentiate by exposure to retinoic acid and dibutyryl cyclic AMP. The increase in steady-state levels of entactin mRNA lagged behind the increase in mRNA for the B2 chain of laminin, suggesting that laminin and entactin are independently rather than coordinately regulated.

Expression of the intracisternal A-particle is elevated during differentiation of embryonal carcinoma cells

Three cDNA clones coding for the 3' region of the intracisternal A-particle (IAP), a mouse endogenous retrovirus, were isolated during screening of a library for genes whose expression was modulated during the retinoic acid-induced differentiation of the embryonal carcinoma cell line F9 into parietal endoderm-like (PE-like) cells. In contrast to previously reported results, no IAP transcripts were detected in either F9 cells or two pluripotent cell lines tested. Instead, IAP transcripts as well as IAPs were abundant in the PE-like cells PYS-2 and F9AcCl 9 and in retinoic acid-induced F9 cells but not in the other differentiated cell types of teratocarcinoma origin which were examined. A comparison of the nucleotide sequences of the three IAP cDNA clones with a genomically integrated proviral sequence (MIA14) demonstrated heterogeneity in both length and sequence among the clones. The position of the poly(A) addition site was determined to be 15 nucleotides from the proposed poly(A) addition signal and to occur after the sequence CAGA, not CA, as previously proposed. Length heterogeneity was greatest in a region of TC repeats 80 base pairs 5' to the poly(A) addition site. Additionally, the putative TATAA box found in MIA14 was deleted in the cDNA clones and in the long terminal repeat regions from two other genomic clones examined. The heterogeneity evident among the cDNA clones further demonstrated that at least two distinct IAP genes are activated during differentiation. An analysis of the rate of transcription in isolated nuclei indicated that the activation of expression of IAP genes in PE-like cells is the result of transcriptional regulation. Together, these observations suggest that the modulation of IAP transcription is regulated autonomously rather than by the fortuitous integration of an IAP sequence adjacent to a developmentally regulated cellular gene.

Control of type IV collagen production in rat mammary epithelial and myoepithelial-like cells

A rat mammary myoepithelial-like cell line (Rama 401) produces 3.5 times more type IV collagen than a mammary epithelial cell line (Rama 25), as measured by the formation of protein hydroxyproline. However, using quantitative "dot" hybridization techniques, the level of poly (A)-containing mRNA hybridizing to a type IV collagen cDNA probe is only 50% higher in Rama 401 cells than in Rama 25 cells. The total amount of hydroxyproline synthesized per cell by the two cell lines is similar. However, in the Rama 25 cells approximately 70% of the hydroxyproline is found as free hydroxyproline against 13% for Rama 401 cells. When Rama 25 cells are grown on collagen gels, they accumulate 2.5-fold more type IV collagen. However, type IV collagen mRNA levels are only 30% higher in Rama 25 cells grown on collagen. The total amount of hydroxyproline synthesized is the same as cells grown on plastic, whereas the extent of collagen degradation is reduced from 71% to 30% in cells grown on collagen gels. No degradation of type IV collagen can be detected in the culture medium of Rama 25 cells. These results indicate that the increased accumulation of type IV collagen in Rama 401 cells is not due to increased synthesis but to a decreased rate of intracellular degradation, and that for Rama 25 cells, the extracellular matrix modulates type IV collagen production by regulating the rate of intracellular collagen degradation.

Discrimination among multiple AATAAA sequences correlates with interspecies conservation of select 3' untranslated nucleotides

The DNA sequence corresponding to the 1.3 kb 3' untranslated region of the 6.5 kb human procollagen alpha 1(IV) mRNA was determined and compared with the mouse sequence obtained from 3' cDNA and genomic clones overlapping the reported 5' half (Oberbaumer et al., 1985, Eur. J. Biochem. 147:217). Although four AAUAAA hexanucleotides are found in the human and seven in the mouse RNAs, Northern blot hybridization showed almost exclusive utilization of the most 3' sequence, in contrast to the pattern seen when using alpha 1(I), alpha 2(I), alpha 1(III) and alpha 2(V) procollagen probes. Moreover, the ninety nucleotides 5' to the poly A tail in the major alpha 1(IV) mRNAs exhibit a much greater degree of interspecies homology than those encompassing the other three shared AAUAAA recognition signals. Further examination of this highly conserved area revealed the presence of two "consensus sequences" found in the 3' noncoding region of a number of RNA polymerase II transcribed genes (Mattaj and Zeller, 1983, Embo J. 2:1883) and, unexpectedly, some similarity with the nucleotides 5' to the poly A attachment signals in other procollagen mRNAs.

Large introns in the 3' end of the gene for the pro alpha 1 (IV) chain of human basement membrane collagen

Using a recently characterized cDNA clone (HT-21) coding for the pro alpha 1 (IV) chain of human type IV procollagen, we have isolated three clones from a bacterio-phage lambda Charon 4A library of human genomic DNA. The intron/exon structure of the pro alpha 1 (IV) genomic clones was analyzed by heteroduplex electron microscopy and nucleotide sequencing. The analysis showed that the introns separating exons 2-9 are large and have a total length of over 12,000 base pairs (bp). Six of seven exons at the 3' end of the gene coded for -Gly-Xaa-Yaa-repeats of the collagenous part of the chain. Five of the -Gly-Xaa-Yaa- coding exons (numbers 5-9) varied in size between 72 bp and 134 bp, and none of them were 54 bp or multiples thereof. A sixth exon (exon 4) was a junction exon containing 71 bp coding for -Gly-Xaa-Yaa- sequences and 142 bp coding for the carboxyl-terminal noncollagenous domain (NC-1). The seventh exon (exon 3, 178 bp) coded for sequences of the NC-1 domain. Five of the six -Gly-Xaa-Yaa- coding exons began with the second base coding for glycine, and only one exon began with a complete glycine codon at the 5' end. The results (i) suggest that the gene for the pro alpha 1(IV) chain of human basement membrane collagen is significantly larger than the genes for fibrillar collagens and (ii) show that it lacks the 54-bp exon repeats characteristic of fibrillar collagen genes.

Expression of the intracisternal A-particle is elevated during differentiation of embryonal carcinoma cells

Three cDNA clones coding for the 3' region of the intracisternal A-particle (IAP), a mouse endogenous retrovirus, were isolated during screening of a library for genes whose expression was modulated during the retinoic acid-induced differentiation of the embryonal carcinoma cell line F9 into parietal endoderm-like (PE-like) cells. In contrast to previously reported results, no IAP transcripts were detected in either F9 cells or two pluripotent cell lines tested. Instead, IAP transcripts as well as IAPs were abundant in the PE-like cells PYS-2 and F9AcCl 9 and in retinoic acid-induced F9 cells but not in the other differentiated cell types of teratocarcinoma origin which were examined. A comparison of the nucleotide sequences of the three IAP cDNA clones with a genomically integrated proviral sequence (MIA14) demonstrated heterogeneity in both length and sequence among the clones. The position of the poly(A) addition site was determined to be 15 nucleotides from the proposed poly(A) addition signal and to occur after the sequence CAGA, not CA, as previously proposed. Length heterogeneity was greatest in a region of TC repeats 80 base pairs 5' to the poly(A) addition site. Additionally, the putative TATAA box found in MIA14 was deleted in the cDNA clones and in the long terminal repeat regions from two other genomic clones examined. The heterogeneity evident among the cDNA clones further demonstrated that at least two distinct IAP genes are activated during differentiation. An analysis of the rate of transcription in isolated nuclei indicated that the activation of expression of IAP genes in PE-like cells is the result of transcriptional regulation. Together, these observations suggest that the modulation of IAP transcription is regulated autonomously rather than by the fortuitous integration of an IAP sequence adjacent to a developmentally regulated cellular gene.