Nuclear factor binding to an AP-1 site is associated with the activation of pro-alpha 1(I)-collagen gene in dedifferentiating chondrocytes

Anti-wrinkling effects of the mixture of vitamin C, vitamin E, pycnogenol and evening primrose oil, and molecular mechanisms on hairless mouse skin caused by chronic ultraviolet B irradiation

BACKGROUND

Naturally occurring antioxidants were used to regulate the skin damage caused by ultraviolet (UV) radiation because several antioxidants have demonstrated that they can inhibit wrinkle formation through prevention of matrix metalloproteinases (MMPs) and/or increase of collagen synthesis.

OBJECTIVE

We examined the effect of oral administration of the antioxidant mixture of vitamin C, vitamin E, pycnogenol, and evening primrose oil on UVB-induced wrinkle formation. In addition, we investigated the possible molecular mechanism of photoprotection against UVB through inhibition of collagen-degrading MMP activity or through enhancement of procollagen synthesis in mouse dorsal skin.

METHODS

Female SKH-1 hairless mice were orally administrated the antioxidant mixture (test group) or vehicle (control group) for 10 weeks with UVB irradiation three times a week. The intensity of irradiation was gradually increased from 30 to 180 mJ/cm2. Microtopographic and histological assessment of the dorsal skins was carried out at the end of 10 weeks to evaluate wrinkle formation. Western blot analysis and EMSA were also carried out to investigate the changes in the balance of collagen synthesis and collagen degradation.

RESULTS

Our antioxidant mixture significantly reduced UVB-induced wrinkle formation, accompanied by significant reduction of epidermal thickness, and UVB-induced hyperplasia, acanthosis, and hyperkeratosis. This antioxidant mixture significantly prevented the UVB-induced expressions of MMPs, mitogen-activated protein (MAP) kinase, and activation of activator protein (AP)-1 transcriptional factor in addition to enhanced type I procollagen and transforming growth factor-beta2 (TGF-beta2) expression.

CONCLUSION

Oral administration of the antioxidant mixture significantly inhibited wrinkle formation caused by chronic UVB irradiation through significant inhibition of UVB-induced MMP activity accompanied by enhancement of collagen synthesis.

Differences in regulation of type I collagen synthesis in primary and passaged hepatic stellate cell cultures: the role of alpha5beta1-integrin

Hepatic stellate cells (HSC) differ in their phenotype depending on the initiation and progression of their activation. Our hypothesis was that different mechanisms govern type I collagen synthesis depending on stage of HSC activation. We investigated the role of alpha(5)beta(1)-integrin as a regulator of type I collagen gene COL1A1 expression in primary and passaged HSC cultures using transgenic mouse containing type I collagen gene COL1A1 promoter linked to the chloramphenicol acetyltransferase (CAT) reporter gene. The alpha(5)beta(1) protein levels increased during the activation and were highest in day 6 primary cultures but decreased in passaged HSC. CAT activity, reflecting COL1A1 expression, was upregulated by alpha(5)beta(1)-integrin. Inhibition of alpha(5)beta(1)-integrin by echistatin and blocking antibody resulted in reduced transgene activity only in early primary cultures (compared with the control, 53.3 +/- 12% echistatin and 58.8 +/- 7% blocking antibody, respectively, P < 0.05). Treatment of passaged HSC with either echistatin or blocking antibody had no effect. Fibronectin, an alpha(5)beta(1)-integrin ligand, increased transgene activity in primary (210 +/- 33%, P < 0.05) but not in passaged HSC cultures (119 +/- 8%). This alpha(5)beta(1)-integrin effect appears to be at least in part mediated by CCAAT enhancer binding protein-beta (C/EBPbeta), because fibronectin increased and alpha(5)-gene silencing by small interfering RNA decreased C/EBPbeta levels. In addition, C/EBPbeta knockout mice showed reduced type I collagen synthesis compared with wild-type littermates. Therefore alpha(5)beta(1)-integrin is an important regulator of type I collagen production in early primary HSC cultures but appears to have no direct role once the HSC are fully activated.

Interaction between Ascorbate and Light-Exposed Riboflavin Induces Lung Remodeling

Light-exposed parenteral multivitamins induce in lungs peroxide-like oxidant responses as well as the initiation of fibrosis. We hypothesized that peroxides generated in light-exposed total parenteral nutrition (TPN) affect lung remodeling. The objective was to assess the specific roles of peroxides, multivitamin preparation (MVP), and light exposure on lung remodeling during TPN. Three-day-old guinea pigs fitted with an indwelling catheter were assigned to the following intravenous regimens: TPN or MVP +/- photoprotection, H(2)O(2)+/- glutathione, MVP +/- metabisulfite, or ascorbic acid +/- riboflavin. Fed animals served as controls. After 4 days, lungs were sampled to determine alveolarization (intercepts), beta-actin mRNA (protection assay), and apoptosis (terminal deoxynucleotidyl transferase dUTP nick-end labeling). Data were analyzed by analysis of variance. The infusion of light-exposed multivitamins induced a 20% lower (p < 0.01) alveolarization index than fed controls, and 3-fold higher (p < 0.01) apoptotic events. This was prevented by photoprotecting TPN. The effect of multivitamins on the alveolarization index was reproduced (p < 0.05) by infusion of light-exposed riboflavin in the presence of vitamin C. The alveolarization index correlated (r(2) = 0.35; p < 0.05) with beta-actin mRNA, suggesting alveolar disruption. Antiperoxides conferred no protection against decreased alveolarization. Lung remodeling induced by exposure of TPN to ambient light is not due to a direct effect of infused peroxides but rather to an interaction between vitamin C and peroxides generated by the exposure of riboflavin to light. It is speculated that this interaction may play a role in the development of chronic lung disease of premature infants who receive TPN and have immature antioxidant defenses.

Control of human articular chondrocyte differentiation by reduced oxygen tension

Cell number is often a limiting factor in studies of chondrocyte physiology, particularly for human investigations. Chondrocytes can be readily proliferated in monolayer culture, however, differentiated phenotype is soon lost. We therefore endeavored to restore normal phenotype to human chondrocytes after serial passage in monolayer culture by manipulating cell morphology and oxygen tension towards the in vivo state. Third passage cells were encapsulated in alginate and exposed to either 20% or more physiologic 5% oxygen tensions. To assess cell phenotype, gene expression was measured using TaqMan real-time PCR. Encapsulated, primary chondrocytes cultured in 20% oxygen were used as a positive reference. Passaged human chondrocytes were fibroblastic in appearance and had lost normal phenotype as evidenced by a decrease in expression of collagen II, aggrecan, and sox9 genes of 66, 6, and 14 fold, respectively; with concomitant high expression of type I collagen (22 fold increase). A partial regaining of the differentiated phenotype was observed by encapsulation in 20% oxygen; however, even after 4 weeks, collagen II gene expression was not fully restored. Collagen II and aggrecan expression were increased, on average, 3 fold, in 5% oxygen tension compared to 20% cultures. Furthermore, matrix glycosaminoglycan (GAG) levels were significantly increased in reduced oxygen. In fact, after 4 weeks in 5% oxygen, encapsulated third passage cells had collagen II expression fully regained and aggrecan and sox9 levels actually exceeding primary cell levels in 20% oxygen. Our results show that the phenotype of serially passaged human articular chondrocytes is more fully restored by combining encapsulation with culture in more physiological levels of oxygen. Sox9, an essential transcription factor for chondrocyte differentiation is strongly implicated in this process since its expression was upregulated almost 27 fold. These findings have implications for the optimal conditions for the in vitro culture of chondrocytes.

The ethanol metabolite, linolenic acid ethyl ester, stimulates mitogen-activated protein kinase and cyclin signaling in hepatic stellate cells

Chronic ethanol consumption can result in hepatic fibrosis and cirrhosis. In addition to oxidative metabolism, ethanol can be metabolized by esterification with fatty acids to form fatty acid ethyl esters (FAEE) such as linolenic acid ethyl ester (LAEE). We have previously demonstrated that LAEE has promitogeinc and activating effects on hepatic stellate cells (HSC), but the mechanisms of these actions are not known. Intracellular signaling through MAP kinase pathways, including extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) can influence the activity of the transcription factor AP-1, while cell-cycle regulatory proteins such as cyclin E and cyclin-dependent kinase (CDK), play an important role in cell proliferation. In this study, we demonstrate that treatment of HSC with LAEE increases cyclin E expression and cyclin E/CDK2 activity, which may underlie the promitogenic effects of this compound. In addition, LAEE increases ERK and JNK activity, and these pathways play an important role in the activation of AP-1-dependent gene expression by LAEE. The stimulation of intracellular signaling pathways in HSC by this well-characterized ethanol metabolite may contribute to ethanol-induced hepatic fibrogenesis.

Photoaging in Asians

The aging process of the skin can be divided into intrinsic and photoaging. Clinically, naturally aged skin is smooth, pale and finely wrinkled. In contrast, photoaged skin is coarsely wrinkled and associated with dyspigmentation and telangiectasia. Although the population of Asia is more than half the population of the Earth, no well-designed study has been undertaken to investigate the characteristics of cutaneous photodamage in Asian skin. As Asian skin is more pigmented, the acute and chronic cutaneous responses to UV irradiation seen in brown skin differ from those in white skin. The clinical characteristics of photoaging in Asian skin, such as pigmentary changes and wrinkle patterns, differ from those of Caucasian skin. This review provides an outline of the characteristic features of photoaging on the brown skin of Asians.

Activation of AP-1 and SP1 correlates with wound growth factor gene expression in glucan-treated human fibroblasts

Glucan is a natural product immunomodulator that has been reported to enhance early wound repair. The mechanism of glucan-stimulated wound repair was thought to be indirect via macrophage release of wound growth factors. However, recent data indicate that there are glucan-specific receptors on human fibroblasts that can modulate cellular function following interaction with the glucan ligand. In this study we examined the effect of glucan on activation of the transcription factors activator protein-1 (AP-1) and specificity protein-1 (Sp1) in normal human dermal fibroblasts. AP-1 and Sp1 are involved in the regulation of cytokine and procollagen genes. In addition, we evaluated the effect of glucan on wound growth factor and vascular endothelial growth factor (VEGF) mRNA expression in primary cultures of normal human dermal fibroblasts. Glucan (1 microg/ml) stimulated fibroblast AP-1 and Sp1 activation in a time-dependent manner, although the temporal kinetics varied between the two transcription factors. AP-1 binding activity was increased (p<0.05) at early time intervals (1, 2, 4, 8 and 12 h), while Sp1 nuclear binding activity was increased (p<0.05) at later time intervals (12, 24, 36 and 48 h). Glucan (1 microg/ml) stimulated fibroblast expression of neurotrophin 3 (NT-3), platelet derived growth factor A (PDGF-A), platelet derived growth factor B (PDGF-B), fibroblast growth factor acidic (aFGF), fibroblast growth factor basic (bFGF), transforming growth factor alpha (TGFalpha), transforming growth factor beta (TGFbeta) and VEGF mRNA at 8 h.

Regulation of type-II collagen gene expression during human chondrocyte de-differentiation and recovery of chondrocyte-specific phenotype in culture involves Sry-type high-mobility-group box (SOX) transcription factors

During ex vivo growth as monolayer cultures, chondrocytes proliferate and undergo a process of de-differentiation. This process involves a change in morphology and a change from expression of chondrocyte-specific genes to that of genes that are normally expressed in fibroblasts. Transfer of the monolayer chondrocyte culture to three-dimensional culture systems induces the cells to re-acquire a chondrocyte-specific phenotype and produce a cartilaginous-like tissue in vitro. We investigated mechanisms involved in the control of the de-differentiation and re-differentiation process in vitro. De-differentiated chondrocytes re-acquired their chondrocyte-specific phenotype when cultured on poly-(2-hydroxyethyl methacrylate) (polyHEMA) as assayed by morphology, reverse transcriptase PCR of chondrocyte-specific mRNA, Western-blot analysis and chondrocyte-specific promoter activity. Essentially, full recovery of the chondrocyte-specific phenotype was observed when cells that had been cultured for 4 weeks on plastic were transferred to culture on polyHEMA. However, after subsequent passages on plastic, the phenotype recovery was incomplete or did not occur. The activity of a gene reporter construct containing the promoter and enhancer from the human type-II collagen gene (COL2A1) was modulated by the culture conditions, so that its transcriptional activity was repressed in monolayer cultures and rescued to some extent when the cells were switched to polyHEMA cultures. The binding of Sry-type high-mobility-group box (SOX) transcription factors to the enhancer region was modulated by the culture conditions, as were the mRNA levels for SOX9. A transfected human type-II collagen reporter construct was activated in de-differentiated cells by ectopic expression of SOX transcription factors. These results underscore the overt change in phenotype that occurs when chondrocytes are cultured as monolayers on tissue-culture plastic substrata.

Apigenin decreases expression of the myofibroblast phenotype

We investigated the effect of the dietary flavonoid apigenin on myofibroblast function. We report that in myofibroblasts treated with apigenin, proliferation and basal levels of alpha1(I) collagen and alpha-smooth muscle actin mRNAs were markedly reduced. Apigenin also attenuated the transforming growth factor-beta-stimulated increases of alpha1(I) collagen and alpha-smooth muscle actin mRNAs. Characterization of the apigenin effects indicates that apigenin reduces both the stability of the alpha1(I) collagen mRNA and the rate of transcription of the alpha1(I) collagen gene through a cycloheximide-sensitive pathway. Western blot analyses indicate that Akt activity is reduced in apigenin-treated myofibroblasts.

Decreased extracellular-signal-regulated kinase and increased stress-activated MAP kinase activities in aged human skin in vivo

The ability of human skin to rejuvenate itself diminishes with the passage of time, resulting in increased fragility. This increased fragility reflects both reduced growth of skin cells and loss of collagenous connective tissue. Oxidative damage plays a central role in cellular aging. Cellular responses to growth signals and oxidative stress are mediated, in part, by growth-factor-activated and stress-activated MAP kinases. We report here that the extracellular-signal-regulated MAP kinase pathway is reduced and the stress-activated MAP kinase pathway is increased in old, compared with young, human skin in vivo. Extracellular-signal-regulated kinase activity was 45% lower in old skin (mean age 84.3 y) relative to young skin (mean age 23.8 y). This lower extracellular- signal-regulated kinase activity resulted from reduced activation, since total extracellular-signal-regulated kinase protein levels did not differ between young and old skin, whereas phosphorylated (i.e., activated) extracellular-signal-regulated kinase protein was reduced 60% in old skin. Cyclin D2, which is regulated by extracellular-signal-regulated kinase and functions to promote cell cycle progression, was reduced 50% in old skin compared with young skin. In contrast, stress-activated MAP kinase activity was elevated 3.4-fold in old skin compared with young skin. This increased activity resulted from enhanced activation, since total stress-activated MAP kinase protein levels were similar in old and young skin. Transcription factor c-Jun, which is activated by stress-activated MAP kinases and promotes expression of connective-tissue-degrading matrix metalloproteinases, was elevated 2-fold in old skin compared with young skin. Treatment of old skin with vitamin A (retinol) for 7 d stimulated extracellular-signal-regulated kinase activity, consistent with its demonstrated ability to stimulate cell growth in old human skin. Taken together, these data indicate that alterations in MAP kinase activities play a key role in the pathophysiology of human skin aging.

Estradiol suppresses type I collagen synthesis in mesangial cells via activation of activator protein-1

BACKGROUND

Estradiol suppresses the synthesis of type I collagen by murine mesangial cells. However, neither the alpha 1(I) nor the alpha 2(I) collagen gene contains an estrogen-response element. Because estradiol modulates the transcription of several genes that lack an estrogen-response element but contain a regulatory activator protein-1 (AP-1) binding motif, we hypothesized that AP-1 may mediate estradiol-induced suppression of type I collagen synthesis.

METHODS

We measured type I collagen synthesis in murine mesangial cells exposed to estradiol, phorbol 12-myristate 13-acetate (an activator of AP-1), or curcumin (an inhibitor of AP-1). We also assessed the effects of estradiol on the steady-state level of c-fos and c-jun mRNA and on the binding of mesangial cell nuclear extracts to an AP-1 consensus binding site oligonucleotide.

RESULTS

Estradiol (10(-10) M to 10(-7) M) suppressed type I collagen synthesis by murine mesangial cells in a dose-dependent manner (10(-7) M, 43.7 +/- 8.2% of control values, P < 0.001). Phorbol 12-myristate 13-acetate (10 microM, four-hr exposure) also decreased type I collagen in the media. In contrast, curcumin (1 microM) increased type I collagen. Estradiol increased the steady-state level of c-fos mRNA twofold at 30 minutes, with a return to basal levels at one hour. This was associated with a greater than threefold increase in the binding of nuclear extracts from estradiol-treated mesangial cells to an AP-1 consensus binding site oligonucleotide. Estradiol-enhanced binding of nuclear extracts to the AP-1 oligonucleotide was reversed by cycloheximide.

CONCLUSIONS

These data suggest that estradiol suppresses collagen I synthesis by murine mesangial cells via enhanced AP-1 activity.

Polyenylphosphatidylcholine inhibits PDGF-induced proliferation in rat hepatic stellate cells

Polyenylphosphatidylcholine (PPC), a polyunsaturated phospholipid extract from soy beans, prevents the development of liver cirrhosis in animal models. Its mechanism of action is unknown. Based on the hypothesis that PPC might act by decreasing hepatic stellate cell proliferation, we studied the effect of PPC and its main components, dilinoleoylphosphatidylcholine (DLPC) and palmitoyl-linoleoylphosphatidylcholine (PLPC), on PDGF-induced stellate cell proliferation and intracellular signal transduction. Normal rat hepatic stellate cells in tissue culture were serumstarved, and incubated with 10ng/ml PDGF in the absence or presence of phospholipids. Cell proliferation was measured by 3H-thymidine incorporation. P44MAPK activation was determined by kinase assay, and AP-1 binding by electrophoretic mobility shift assay. PPC (200 ng/ml) significantly inhibited PDGF-induced proliferation (p < 0.05; ANOVA, n = 3) and antagonized PDGF-induced P44MAPK activation and AP-1 binding. This effect was mimicked by DLPC but not by PLPC. Neither DLPC nor PLPC prevented PDGF receptor activation. We conclude that PPC exerts a previously unrecognized effect on mitogen-induced stellate cell proliferation which may be mediated by DLPC. Inhibition of this cascade represents a potential mechanism for the inhibitory effect of PPC on hepatic fibrogenesis.

Suppression of NF-kappa B and AP-1 activation by glucocorticoids in experimental glomerulonephritis in rats: molecular mechanisms of anti-nephritic action

Transcription factors nuclear factor-kappa B (NF-kappa B) and activator protein-1 (AP-1) play an important role in the induction of pro-inflammatory factors such as cytokines and cell adhesion molecules, which could be involved in the pathogenesis of glomerulonephritis. We have recently reported the pathogenic significance of NF-kappa B activation in experimental glomerulonephritis in rats. In this study, we investigated the pathogenic relevance of AP-1 activation in nephrotoxic serum (NTS)-induced glomerulonephritis. Increased AP-1 DNA-binding activity was detected in nephritic glomeruli by a gel shift assay. The kinetics of AP-1 activation was similar to that of NF-kappa B. Activation of both NF-kappa B and AP-1 preceded proteinuria, an important pathophysiological parameter for glomerulonephritis. Treatment with prednisolone, a glucocorticoid hormone, prevented activation of both NF-kappa B and AP-1 in glomeruli and subsequent mRNA expression of NF-kappa B- and AP-1-regulated genes. Prednisolone was also effective therapeutically and reduced DNA-binding activities of NF-kappa B and AP-1 which are already activated in nephritic glomeruli. These results suggest that activated NF-kappa B and AP-1 may play an important pathogenic role in glomerulonephritis and the anti-nephritic action of glucocorticoids may be mediated through the suppression of these transcription factors.

Osteogenic protein-1 up-regulation of the collagen X promoter activity is mediated by a MEF-2-like sequence and requires an adjacent AP-1 sequence

Bone morphogenetic proteins induce chondrogenesis and osteogenesis in vivo. To investigate molecular mechanisms involved in chondrocyte induction, we examined the effect of osteogenic protein (OP)-1/bone morphogenetic protein-7 on the collagen X promoter. In rat calvaria-derived chondrogenic C5.18 cells, OP-1 up-regulates collagen X mRNA levels and its promoter activity in a cell type- specific manner. Deletion analysis localizes the OP-1 response region to 33 bp (-310/-278), which confers OP-1 responsiveness to both the minimal homologous and heterologous Rous sarcoma virus promoter. Transforming growth factor-beta2 or activin, which up-regulates the expression of a transforming growth factor-beta-inducible p3TP-Lux construct, has little effect on collagen X mRNA and on this 33-bp region. Mutational analysis shows that both an AP-1 like sequence (-294/-285, TGAATCATCA) and an A/T-rich myocyte enhancer factor (MEF)-2 like sequence (-310/-298, TTAAAAATAAAAA) in the 33-bp region are necessary for the OP-1 effect. Gel shift assays show interaction of distinct nuclear proteins from C5.18 cells with the AP-1-like and the MEF-2-like sequences. OP-1 rapidly induces nuclear protein interaction with the MEF-2-like sequence but not with the AP-1 like sequence. MEF-2-like binding activity induced by OP-1 is distinct from the MEF-2 family proteins present in C2C12 myoblasts, in which OP-1 does not induce collagen X mRNA or up-regulate its promoter activity. In conclusion, we identified a specific response region for OP-1 in the mouse collagen X promoter. Mutational and gel shift analyses suggest that OP-1 induces nuclear protein interaction with an A/T-rich MEF-2 like sequence, distinct from the MEF-2 present in myoblasts, and up-regulates collagen X promoter activity, which also requires an AP-1 like sequence.

Detection and characterization of Sp1 binding activity in human chondrocytes and its alterations during chondrocyte dedifferentiation

We have detected DNA binding activity for a synthetic oligonucleotide containing an Sp1 consensus sequence in nuclear extracts from human chondrocytes. Changes in the levels of Sp1 oligonucleotide binding activity were examined in nuclear extracts from freshly isolated human chondrocytes, from chondrocytes that had been cultured under conditions that allowed the maintenance of a chondrocyte-specific phenotype on plastic dishes coated with the hydrogel poly(2-hydroxyethyl methacrylate), and from chondrocytes induced to dedifferentiate into fibroblast-like cells by passage in monolayer culture on plastic substrata. It was observed that Sp1 binding was 2-3-fold greater in nuclear extracts from dedifferentiated chondrocytes than in nuclear extracts from either freshly isolated chondrocytes or from cells cultured in suspension. The Sp1 binding activity was specific, since it was competed by unlabeled Sp1 but not by AP1 or AP2. The addition of a polyclonal antibody against Sp1 to nuclear extracts from freshly isolated chondrocytes or to extracts isolated from chondrocytes cultured in monolayer decreased the binding of Sp1 by approximately 85%. However, when the same experiment was carried out with nuclear extracts prepared from cells cultured on poly(2-hydroxyethyl methacrylate)-coated plates, only a very slight inhibition of Sp1 binding was observed. When fragments of the COL2A1 promoter containing putative Sp1 binding sites amplified by polymerase chain reaction were examined, it was found that the amounts of DNA-protein complex formed with nuclear extracts from dedifferentiated chondrocytes were 2-3-fold greater than the amounts formed with nuclear extracts from freshly isolated chondrocytes or from cells cultured in suspension. Quantitation of DNA binding activity by titration experiments demonstrated that nuclear extracts from fibroblast-like cells contained approximately 2-fold greater Sp-1 specific binding activity than nuclear extracts from chondrocytes. The direct role of Sp1 in type II collagen gene transcription was demonstrated by co-transfection experiments of COL2A1 promoter-CAT constructs in Drosophila Schneider line L2 cells that lack Sp1 homologs. This is the first demonstration of Sp1 binding activity in human chondrocytes and of differences in Sp1 DNA binding activity between differentiated and dedifferentiated chondrocytes.

Surface adhesion-mediated regulation of chondrocyte-specific gene expression in the nontransformed RCJ 3.1C5.18 rat chondrocyte cell line

Recent evidence suggests that decreased chondrocyte function in osteoarthritis and other articular disorders may be due to chondrocyte dedifferentiation produced by altered regulatory signals from the cartilage extracellular matrix (ECM). However, there are currently no mammalian chondrocytic cell line systems adapted to the study of this process. We therefore examined the effects of ECM growth conditions on markers of differentiated chondrocytic phenotype expression in the nontransformed rat RCJ 3.1C5.18 (RCJ) chondrocyte cell line, including type II collagen expression, aggrecan production, link protein gene expression, and parathyroid hormone (PTH) receptor number. RCJ cells grown in monolayer on plastic exhibited a dedifferentiated phenotype characterized by flattened cell morphology, with > 80% type I collagen and < 5% type II collagen production, as determined by two-dimensional gel mapping electrophoresis of collagen cyanogen bromide peptides. In addition, aggrecan production was low, and link protein mRNA was not expressed at detectable levels. After transfer to growth under minimal attachment conditions on the surface of a composite type I collagen/agarose (0.15%-0.8%) gel (CAG) for 7 days, RCJ cells developed a rounded, chondrocytic morphology and a pattern of differentiated, chondrocytic gene expression, with 79% type II and 8% type I collagen production. Steady-state type I and type II procollagen mRNA levels were altered in parallel with collagen protein expression. In cells grown on CAG, aggrecan production increased 6-fold, and there was a marked increase in both aggrecan core protein and link protein mRNA levels. In addition, maximal PTH-stimulated cAMP generation increased 15-fold in association with an increased PTH receptor number. Therefore, the RCJ chondrocyte cell line is highly sensitive to ECM regulation of chondrocyte-specific gene expression.

Transcriptional repression of the alpha 1(I) collagen gene by ras is mediated in part by an intronic AP1 site

We have previously shown that transformation of fibroblasts by ras results in transcriptional inhibition of the alpha 1(I) gene. An alpha 1(I)-hGH chimeric plasmid containing 3.7 kb of 5' flanking and 4.4 kb of alpha 1(I) transcribed sequence was regulated appropriately by ras in a transient transfection assay. In contrast, a similar plasmid containing alpha 1(I) DNA from -220 to +500 was virtually unresponsive to ras. The regions from -3700 to -220 and +500 to +4400 contributed equally to the ras-mediated inhibition of the parental plasmid. Deletion analysis indicated that a short fragment, between +500 and +890 in the first intron of the alpha 1(I) gene, was recognized differently in ras-transformed and wild-type cells. A previously described AP1 site in this fragment stimulated alpha 1(I) transcription in Rat1 fibroblasts but was inactive in ras-transformed cells. Mobility shift assays using nuclear extracts from the two cell types demonstrated differences in binding to the alpha 1(I) AP1 site. We conclude that ras transformation suppresses the function of a cell-specific enhancer in the first intron of the alpha 1(I) collagen gene.

Tissue-specific expression of the gene for type I procollagen (COL1A1) in transgenic mice. Only 476 base pairs of the promoter are required if collagen genes are used as reporters

Inconsistent data have been reported on the size of the promoter that is necessary for high levels of tissue-specific expression of the COL1A1 gene for type I procollagen. Some of the inconsistencies may be traced to the use of reporter gene constructs. Therefore, we prepared transgenic mice with modifications of the intact gene engineered so that the level of expression of the transgene could be assayed both as mRNA and protein that were similar to the products from the endogenous COL1A1 gene. The results with a mini-COL1A1 gene lacking 41 internal exons and introns indicated that the first intron and 90% of the 3'-untranslated region were not essential for tissue-specific expression. In a hybrid COL1A1/COL2A1 construct, a 1.9-kilobase 5'-fragment from the COL1A1 gene that contained only 476 of the promoter was linked to a promoterless 29.5-kilobase fragment of the human COL2A1 gene for type II procollagen. The hybrid COL1A1/COL2A1 construct was expressed as both mRNA and protein in tissues that normally synthesize type I procollagen but not type II procollagen. Apparently, 476 base pairs of the promoter are sufficient to drive tissue-specific expression of the COL1A1 gene and totally inappropriate expression of the COL2A1 gene.

Cell-specific expression of alpha 1(I) collagen-hGH minigenes in transgenic mice

Sequences within the first intron of the alpha 1(I) collagen gene have been implicated in the regulation of expression of alpha 1(I) collagen-reporter gene constructs in cultured cells. However, the physiological significance of these intronic elements has not been established. We have used in situ hybridization to examine whether a cell-specific pattern of expression of human alpha 1(I) collagen-human growth hormone minigenes exists in transgenic mice. Our results indicate that transgenes which contained 2,300 bp of promoter/5' flanking sequence and an intact first intron were well expressed by fibroblasts in dermis and fascia, whereas transgenes lacking the intronic sequence, +292 to +1440, were not expressed in dermis and poorly expressed in fascia. Analysis of transgene expression in cultured fibroblasts obtained from dermal explants of transgenic animals confirmed the requirement for these intronic sequences in the regulation of the alpha 1(I) collagen gene. In contrast, transgenes with or without the intronic deletion were expressed equally well in tendon and bone, in a manner comparable to the endogenous mouse alpha 1(I) collagen gene, and expression of neither transgene was detected in skeletal muscle or perichondrium. These data support a model in which cis-acting elements in the first intron, and their cognate DNA-binding proteins, mediate transcription of the alpha 1(I) collagen gene in some cells, such as dermal fibroblasts, but not in tendon cells or osteoblasts. Moreover, regions of the gene not included in the sequence, -2300 to +1440, appear to be required for transcription in tissues such as skeletal muscle and perichondrium.

Nuclear and cytoplasmic alpha 1 (I) collagen mRNA-binding proteins

We have recently identified a cytoplasmic protein, alpha 1-RBF67, that specifically interacts with the conserved 3'-untranslated region of the alpha 1 (I) collagen gene. The binding activity was decreased in extracts from dexamethasone treated cells, which correlates with the known accelerated turnover of the COL1A1 RNA [Määttä, A. and Penttinen, R.P.K. (1993) Biochem. J. 295, 691-698]. Now we report that a very similar protein is present in nuclear extracts of NIH 3T3, human fibroblast and HeLa cells, which suggests that determination of cytoplasmic mRNA stability is not the sole function of the alpha 1-RBF67 activity. The binding to the RNA probe can be inhibited by annealing a DNA oligonucleotide or using excess of cold specific competitors. In UV-cross linking assays the nuclear protein has the same molecular weight (67 kDa) as the cytoplasmic one and the RNA-bound peptides generated by CNBr or V8 protease cleavage from both the cytoplasmic and the nuclear protein were identical. This protein was the only one of several nuclear collagen mRNA 3'-UTR binding proteins that was present in both nuclear and cytoplasmic extracts. In fibroblasts heparin-resistant nuclear RNA binding proteins had molecular weights of 45, 67 (alpha 1-RBF67), and 71 kDa. HeLa-cells contained an additional protein of 51 kDa and several non-specific RNA-binding proteins. The binding activity is modified by changes in the redox state, which implicates that in the nucleus the binding affinities of alpha 1(I) collagen RNA-binding protein and AP-1, a redox sensitive nuclear factor, that is important in the transcription of alpha 1(I) collagen gene, can be regulated simultaneously to the same direction.