The compliance of collagen gels regulates transforming growth factor-beta induction of alpha-smooth muscle actin in fibroblasts

Wound contraction is mediated by myofibroblasts, specialized fibroblasts that appear in large numbers as the wound matures and when resistance to contractile forces increases. We considered that the regulation of myofibroblast differentiation by wound-healing cytokines may be dependent on the resistance of the connective tissue matrix to deformation. We examined transforming growth factor-beta1 (TGF-beta1) induction of the putative fibroblast contractile marker, alpha-smooth muscle actin (alpha-SMA), and the regulation of this process by the compliance of collagen substrates. Cells were cultured in three different types of collagen gels with wide variations of mechanical compliance as assessed by deformation testing. The resistance to collagen gel deformation determined the levels of intracellular tension as shown by staining for actin stress fibers. For cells plated on thin films of collagen-coated plastic (ie, minimal compliance and maximal intracellular tension), TGF-beta1 (10 ng/ml; 6 days) increased alpha-SMA protein content by ninefold as detected by Western blots but did not affect beta-actin content. Western blots of cells in anchored collagen gels (moderate compliance and tension) also showed a TGF-beta1-induced increase of alpha-SMA content, but the effect was greatly reduced compared with collagen-coated plastic (<3-fold increase). In floating collagen gels (high compliance and low tension), there were only minimal differences of alpha-SMA protein. Northern analyses for alpha-SMA and beta-actin indicated that TGF-beta1 selectively increased mRNA for alpha-SMA similar to the reported protein levels. In pulse-chase experiments, [35S]methionine-labeled intracellular alpha-SMA decayed most rapidly in floating gels, less rapidly in anchored gels, and not at all in collagen plates after TGF-beta1 treatment. TGF-beta1 increased alpha2 and beta1 integrin content by 50% in cells on collagen plates, but the increase was less marked on anchored gels and was undetectable in floating gels. When intracellular tension on collagen substrates was reduced by preincubating cells with blocking antibodies to the alpha2 and beta1 integrin subunits, TGF-beta1 failed to increase alpha-SMA protein content in all three types of collagen matrices. These data indicate that TGF-beta1-induced increases of alpha-SMA content are dependent on the resistance of the substrate to deformation and that the generation of intracellular tension is a central determinant of contractile cytoskeletal gene expression.     

转化生长因子β2对人晶状体上皮细胞E-钙黏素和α-平滑肌肌动蛋白表达的影响

背景：有研究表明,人晶状体上皮细胞的间质转分化是后发性白内障的主要病理改变,转化生长因子β2可以诱导间质转分化的发生。 目的：体外培养人晶状体上皮细胞,观察转化生长因子β2对人晶状体上皮细胞转分化相关蛋白E-钙黏蛋白和α-平滑肌肌动蛋白表达的影响。 方法：利用组织块法体外培养人晶状体上皮细胞并传代,选择传5代的细胞进行实验,采用100 ng/L转化生长因子β2诱导48 h,反转录-聚合酶链反应方法检测E-钙黏蛋白、α-平滑肌肌动蛋白mRNA的表达,应用蛋白质印迹法Western blot检测其蛋白表达。 结果与结论：转化生长因子β2处理人晶状体上皮细胞48 h后,细胞E-钙黏蛋白表达明显减弱,α-平滑肌肌动蛋白的表达明显增强。提示转化生长因子β2可以成功诱导晶状体上皮细胞间质转分化,转化生长因子β2处理的晶状体上皮细胞可以作为间质转分化的细胞模型。     

Regulation of alpha-smooth muscle actin expression in granulation tissue myofibroblasts is dependent on the intronic CArG element and the transforming growth factor-beta1 control element

Myofibroblasts are specialized contractile fibroblasts that are critical in wound closure and tissue contracture. Generation of contractile force is correlated with the expression of alpha-smooth muscle actin (alpha-SMA); however, little is known regarding molecular mechanisms that control activation of alpha-SMA in myofibroblasts in granulation tissue. The aims of the present studies were to identify sufficient promoter regions required for alpha-SMA expression in myofibroblasts in vivo and to determine whether activation of alpha-SMA expression in myofibroblasts in vivo is dependent on an intronic CArG [CC(A/T)6GG] and a transforming growth factor-beta1 control element (TCE) that are required for alpha-SMA expression in smooth muscle cells. A Lac Z transgene construct from -2600 through the first intron was expressed in myofibroblasts within granulation tissue of cutaneous wounds in a pattern that closely mimicked endogenous alpha-SMA expression. Mutation of either the intronic CArG element or the TCE completely inhibited transgene expression in myofibroblasts in granulation tissue and responsiveness to transforming growth factor-beta1 in cultured transgenic fibroblasts. These same elements were also critical in regulating alpha-SMA expression during skeletal muscle repair but not during skeletal muscle development. Taken together, these results provide the first in vivo evidence for the importance of the intronic CArG and TCE cis-elements in the regulation of alpha-SMA expression in myofibroblasts in granulation tissue.     

Induction of transforming growth factor-beta 1 production in human cells by herpes simplex virus.

Transforming growth factor-beta (TGF-beta) is a cytokine of particular interest in human retrovirus infections because it can abrogate antigen-specific cellular activation. Although TGF-beta production has been observed in HIV infections, there is no evidence that herpes simplex virus (HSV)-stimulated human cells produce this cytokine. Here we present evidence, for the first time, that in vitro infection of human mononuclear cells with HSV type 1 (HSV-1) induced the release of TGF-beta1 protein. The production of this cytokine was time dependent and was found highly significant (p < 0.001) after 48 h. In addition, we observed that the secretion of TGF-beta1 was dependent on the concentration of human cells. It was found that virus needs to replicate in human cells for the production of TGF-beta1, as UV-inactivated virus did not induce significant production of cytokine protein. Interestingly, increased HSV-1-induced TGF-beta1 production in cultures containing antiinterleukin (IL)-12 or antiinterferon (IFN)-gamma antibodies was observed, whereas an irrelevant antibody had no effect on the production of this cytokine. Taken together, these findings indicate that human cells synthetize TGF-beta1 in response to HSV-1 and at the same time suggest that HSV-1-induced TGF-beta1 production may be one of the mechanisms by which HSV can at least partly evade activation of the host immune system.     

Heparin induces alpha-smooth muscle actin expression in cultured fibroblasts and in granulation tissue myofibroblasts.

BACKGROUND: Heparin increases alpha-smooth muscle actin expression in smooth muscle cells in vivo and in vitro. It has been recently suggested that alpha-smooth muscle actin expression in fibroblasts is a marker of myofibroblastic differentiation. We have examined the effect of heparin and of four nonanticoagulant heparin derivatives on alpha-smooth muscle actin expression by fibroblasts in vitro and in vivo. EXPERIMENTAL DESIGN: For in vitro experiments, heparin was added for 7 days to different fibroblastic cultures. We studied cell proliferation and alpha-smooth muscle actin protein and mRNA expression. For in vivo studies, osmotic minipumps filled with NaCl or tumor necrosis factor-alpha without or with nonanticoagulant heparin were implanted subcutaneously. After 14 days, newly accumulated connective tissues around the pumps were processed for immunofluorescence and electron microscopic and biochemical studies. RESULTS: In vitro, heparin inhibited proliferation and increased the expression of alpha-smooth muscle actin protein and mRNA. Analysis of [3H]thymidine incorporation in synchronized cells suggested that heparin produces a selection of alpha-smooth muscle actin expressing cells. In vivo, the local application of tumor necrosis factor-alpha resulted in formation of a typical granulation tissue: immunofluorescence showed that accumulated fibroblastic cells express alpha-smooth muscle actin only in the presence of heparin derivatives. In tumor necrosis factor-alpha treated animals, electron microscopic examination established the presence of myofibroblasts, but alpha-smooth muscle actin was expressed in microfilament bundles only in the presence of heparin derivatives. CONCLUSIONS: These results show that heparin and its nonanticoagulant derivatives influence the expression of alpha-smooth muscle actin in fibroblastic cells both in vitro and in vivo and that this effect is probably related to the selection of a particular cell subpopulation. They suggest a possible role for heparin during the formation and evolution of granulation tissue.     

Induction of the interleukin 1 receptor antagonist protein by transforming growth factor-beta.

Transforming growth factor-beta 1 (TGF-beta 1) mediates many immunosuppressive effects on immune cells and can inhibit the production of tumor necrosis factor and interleukin 1 (IL 1). However, TGF-beta 1 can stimulate the production of IL 6 and platelet-derived growth factor, indicating that TGF-beta 1 initiates complex effects on the production of cytokines. In this report we show that treatment of peripheral blood monocytes with TGF-beta 1 leads to the induction of a recently described IL 1 receptor antagonist protein (IRAP). The effect of TGF-beta 1 was both dose and time dependent. TGF-beta 1 induced de novo synthesis of IRAP, as Northern blotting experiments indicated a rapid and transient induction of the mRNA encoding IRAP. The induction of IRAP suggests a potential mechanism by which some of the inhibitory effects of TGF-beta 1 are mediated.     

Induction of cardiac fibrosis by transforming growth factor-beta(1)

The role of transforming growth factor-beta(1) (TGF-beta(1)) in the production and deposition of collagens and in the induction of gene expression in the myocardium in relation to the development of myocardial fibrosis will be discussed. Very low expression of TGF-beta(1) and collagen type I and III mRNA is seen in the normal rat heart. Both expressions are markedly increased in the infarcted heart and the levels of TGF-beta(1) mRNA precedes increases in mRNA levels for extracellular matrix (ECM) proteins, suggesting a possible role of TGF-beta(1) in remodeling processes in the myocardium. The TGF-beta(1) expression is normally only transient since continuous TGF-beta(1) overexpression seems to promote nonadaptive cardiac hypertrophy and myocardial fibrosis. In vitro, TGF-beta(1) induces an increase in collagen production and secretion and enhances the abundance of mRNA levels for collagen type I and III in rat cardiac fibroblasts in culture. TGF-beta(1) also stimulates in vivo the expression of ECM proteins and in vivo gene transfer of TGF-beta(1) can induce myocardial fibrosis. Increased myocardial TGF-beta(1) and ECM protein mRNA are found in myocardial fibrosis induced by angiotensin II infusion, by noradrenaline treatment, by isoprenaline infusion, and by long-term blockade of NO synthesis. In vivo antagonism of TGF-beta(1) by neutralizing anti-TGF-beta(1) antibodies or by proteoglycans prevents the increase in gene expression of ECM proteins and inhibits myocardial fibrosis, suggesting that the increases in matrix protein production and fibrosis are mediated by TGF-beta(1).     

Distribution of transforming growth factor-beta 1 in human astrocytomas.

We used immunohistochemical techniques to study the distribution of transforming growth factor-beta 1 (TGF-beta 1) and infiltrating lymphocytes and macrophages in human astrocytomas. Thirteen of 15 grade 4 astrocytomas (glioblastomas) showed staining with anti-TGF-beta 1 antibody, predominantly in proliferating endothelial complexes and surrounding small and medium-sized blood vessels. Brain tissue microscopically free of tumor cells (n = 8) and more differentiated astrocytomas of varying grade (1 to 3; n = 6) devoid of endothelial proliferation did not stain with anti-TGF-beta 1. Normal brain contained only rare lymphoreticular cells. The majority of astrocytomas studied, however, contained T lymphocytes and macrophages with smaller numbers of B lymphocytes. The lymphoreticular infiltrates were concentrated primarily in close proximity to blood vessels. Within an individual tumor perivascular regions staining for TGF-beta 1 never contained more than occasional T lymphocytes. Perivascular regions not staining for TGF-beta 1 frequently contained low to high numbers of T lymphocytes. The inverse relationship in the distribution of TGF-beta 1 and lymphocyte infiltrates is compatible with a functional relationship between this cytokine and an immune effector cell response to glioblastomas.     

Inhibition of human neutrophil degranulation by transforming growth factor-beta1

Neutrophils enter tissues including the uterus and are found in the endometrium in increased numbers prior to menses. In this environment, they are exposed to transforming growth factor (TGF)-beta1 produced by endometrial stromal and epithelial cells. We observed that incubation of neutrophils in vitro with TGF-beta1 at 1 pg/ml significantly reduced their secretion of lactoferrin in response to lipopolysaccharide (LPS). This effect was achieved with as little as 15 min of pretreatment with TGF-beta1. Inhibition of lactoferrin release by TGF-beta1 was observed irrespective of whether neutrophils were stimulated by ligands for Toll-like receptor (TLR)-2, TLR-4 or FPR, the G protein-coupled receptor for formylated peptides. Inhibition by TGF-beta1 was negated by SB-431542, a small molecule inhibitor that specifically blocks the kinase activity of the type I TGF-beta receptor (ALK5) In contrast to lactoferrin release, another important neutrophil function, interleukin (IL)-8 driven chemotaxis, was not affected by TGF-beta1 at 1 pg/ml or 100 pg/ml. We conclude that in tissues of the female reproductive tract, TGF-beta1 inhibition of neutrophil degranulation may prevent these cells from initiating an inflammatory response or releasing degradative enzymes that could potentially damage the oocyte or fetus.     

Induction of transforming growth factor-beta and prostaglandin E2 production by ethanol in human monocytes.

To test our hypothesis that monocytes (M phi) and their mediators are major contributors to ethanol-related immunodepression, the modulating capacity of acute ethanol treatment was assessed on the production of transforming growth factor-beta (TGF beta) and prostaglandin E2 (PGE2) by human peripheral blood M phi. We demonstrate that acute in vitro treatment of adherent M phi with either 50 or 150 mM ethanol induced a significant increase in the production of TGF beta (P < 0.045 and P < 0.001, respectively). Furthermore, M phi pretreatment with both 50 and 150 mM ethanol augmented TGF beta production in response to subsequent stimulation with the synthetic bacterial analog, muramyl dipeptide (MDP) (P < 0.05 and P < 0.001, respectively). Ethanol also increased TGF beta production in interferon gamma (IFN gamma-activated M phi in response to MDP stimulus (P < 0.05). M phi TGF beta levels, however, were always lower in IFN gamma-activated than in non-IFN gamma-activated M phi after the same stimulation with ethanol plus MDP, suggesting that M phi preactivation by IFN gamma can partially counteract the TGF beta inducing potential of ethanol. Similar to its TGF beta-inducing potential, ethanol (150 mM) had the capacity to induce PGE2 production in adherent human M phi (P < 0.045). However, ethanol failed to augment M phi PGE2 production induced by the PGE2 secretagogue, MDP. TGF beta induction by ethanol was unaffected by the presence of cyclooxygenase inhibitor, suggesting that ethanol-induced M phi TGF beta production does not require M phi PGE2 production. These results indicate that ethanol is a potent inducer for inhibitory M phi mediators, TGF beta and PGE2, and also has the capacity to augment M phi TGF beta production in response to subsequent stimulation. Thus, ethanol-induced elevation of M phi TGF beta and PGE2 production might contribute to decreased T cell proliferation and abnormal M phi functions after alcohol exposure, resulting in a depressed immune response.     

Modulation of human IgE synthesis by transforming growth factor-beta.

Exogenous transforming growth factor-beta 2 (TGF-beta 2) markedly inhibits the interleukin 4 (IL4)-stimulated synthesis of human IgE in three models where the B cell co-stimulation signals are contact dependent. This concerns T cell-dependent IgE production by (i) unfractionated peripheral blood mononuclear cells (PMBC) cultured with IL4 and (ii) highly purified B cells cocultured with irradiated EL4 thymoma cells in the presence of IL4 and phorbol myristate acetate, as well as monocyte-dependent IgE production by rigorously T cell-depleted PBMC cultured with IL4 and hydrocortisone. The suppression is not isotype specific. TGF-beta exerts its effect by inhibiting the proliferation of B cells and perhaps also the differentiation of proliferating B cells. However, at a later stage of differentiation, IgE B cells are refractory to the inhibitory effect of TGF-beta, as shown by the slight but significant increase of the spontaneous secretion of IgE by PBMC of atopic patients. This enhancement is due to the suppression of endogenous interferon-gamma production. Most interestingly the synthesis of IgE by highly purified B cells costimulated with IL4 and Epstein-Barr virus is unaffected by TGF-beta. It is concluded that TGF-beta mainly acts by inhibiting IL4-supported B cell proliferation; however, its effects depend upon the B cell costimulation signals that are required together with IL4 for the induction of IgE synthesis.     

Melanoma-associated expression of transforming growth factor-beta isoforms.

Melanocytic neoplasia is characterized by the aberrant overproduction of multiple cytokines in vitro. However, it is largely unknown how cytokine expression relates to melanoma progression in vivo. Transforming growth factor beta (TGF-beta) is a multifunctional cytokine commonly produced by cultured melanoma cells. The in situ expression of all three TGF-beta isoforms (TGF-beta1, -2, and -3) was determined immunohistochemically in melanocytes and in 51 melanocytic lesions using isoform-specific antibodies. Significant linear trends of expression were observed from melanocytes through nevi and primary and metastatic melanomas for all three isoforms. TGF-beta1 was expressed by some melanocytes and almost uniformly by nevi and melanomas. TGF-beta2 and -3 were not expressed in normal melanocytes but were expressed in nevi and early and advanced primary (radial and vertical growth phase) and metastatic melanomas in a tumor-progression-related manner. TGF-beta2 was heterogeneously expressed in advanced primary and metastatic melanomas, whereas TGF-beta3 was uniformly and highly expressed in these lesions. Thus, expression of TGF-beta isoforms in melanocytes and melanocytic lesions is heterogeneous and related to tumor progression, and expression of TGF-beta2 and TGF-beta3 commences at critical junctures during progression of nevi to primary melanomas.     

Transforming growth factor-beta1 induces transforming growth factor-beta1 and transforming growth factor-beta receptor messenger RNAs and reduces complement C1qB messenger RNA in rat brain microglia

Transforming growth factor-beta1 is a multifunctional peptide with increased expression during Alzheimer's disease and other neurodegenerative conditions which involve inflammatory mechanisms. We examined the autoregulation of transforming growth factor-beta1 and transforming growth factor-beta receptors and the effects of transforming growth factor-beta1 on complement C1q in brains of adult Fischer 344 male rats and in primary glial cultures. Perforant path transection by entorhinal cortex lesioning was used as a model for the hippocampal deafferentation of Alzheimer's disease. In the hippocampus ipsilateral to the lesion, transforming growth factor-beta1 peptide was increased >100-fold; the messenger RNAs encoding transforming growth factor-beta1, transforming growth factor-beta type I and type II receptors were also increased, but to a smaller degree. In this acute lesion paradigm, microglia are the main cell type containing transforming growth factor-beta1, transforming growth factor-beta type I and II receptor messenger RNAs, shown by immunocytochemistry in combination with in situ hybridization. Autoregulation of the transforming growth factor-beta1 system was examined by intraventricular infusion of transforming growth factor-beta1 peptide, which increased hippocampal transforming growth factor-beta1 messenger RNA levels in a dose-dependent fashion. Similarly, transforming growth factor-beta1 increased levels of transforming growth factor-beta1 messenger RNA and transforming growth factor-beta type II receptor messenger RNA (IC(50), 5pM) and increased release of transforming growth factor-beta1 peptide from primary microglia cultures. Interactions of transforming growth factor-beta1 with complement system gene expression are also indicated, because transforming growth factor-beta1 decreased C1qB messenger RNA in the cortex and hippocampus, after intraventricular infusion, and in cultured glia. These indications of autocrine regulation of transforming growth factor-beta1 in the rodent brain support a major role of microglia in neural activities of transforming growth factor-beta1 and give a new link between transforming growth factor-beta1 and the complement system. The auto-induction of the transforming growth factor-beta1 system has implications for transgenic mice that overexpress transforming growth factor-beta1 in brain cells and for its potential role in amyloidogenesis.     

Density-dependent inhibition of cell growth by transforming growth factor-beta 1 in normal human fibroblasts

We report here that transforming growth factor-beta 1 (TGF-beta 1) inhibits platelet-derived growth factor (PDGF)-induced DNA synthesis in normal human fibroblasts in a cell density-dependent manner; no inhibition was seen in sparse cultures, approximately 50% inhibition in confluent cell cultures, and an almost total inhibition in dense cultures. The PDGF-inducible genes c-myc and c-fos were induced also by TGF-beta 1. Simultaneous addition of TGF-beta 1 and PDGF resulted in sustained, rather than transient, expression of c-fos mRNA; c-fos mRNA was detected as long as 24 hr after addition of PDGF and TFG-beta 1. TGF-beta 1 also induced mRNA for the A chain, but not the B chain, of PDGF. Conversely, PDGF induced TGF-beta 1 mRNA in sparse but not in dense cultures. These data indicate the existence of a complex interdependent regulation of PDGF and TGF-beta mRNA expression which is influenced by the cell density.     

Expression of alpha-smooth muscle actin in liver diseases.

To evaluate the distribution of alpha-smooth muscle actin (alpha-SMA) positive cells in various liver diseases, we undertook an immunohistochemical study of liver diseases including chronic persistent hepatitis, chronic active hepatitis, liver cirrhosis, intrahepatic cholelithiasis and hepatocellular carcinoma. As a control, fetal livers (gestational age: 22-26 weeks) showed alpha-SMA positive cells along the blood vessels of the portal area, terminal hepatic venules and at perisinusoidal spaces. Perisinusoidal alpha-SMA positive cells were bipolar shaped and had round nuclei. In chronic persistent hepatitis, a few alpha-SMA positive cells were admixed with the inflammatory infiltrates mostly along the intact limiting plate. They were also detected multifocally in a linear pattern along the dilated sinusoid. In chronic active hepatitis, very strong alpha-SMA staining was detected at the site of piecemeal necrosis and adjacent lobules. A-SMA expression was decreased in some cases after interferon treatment. In cases of transplanted liver biopsies, expression of intralobular alpha-SMA was diffusely increased but showed no correlation with degree of acute rejection. Cirrhotic livers revealed strong alpha-SMA positivity in fibrous septae as well as in the perisinusoidal space of intact hepatocytes at the leading edge of fibrosis. Interlobular bile ducts were concentrically circumscribed by alpha-SMA positive cells in cases of intrahepatic cholelithiasis. In trabecular type hepatocellular carcinomas, most sinusoidal lining cells were positive for alpha-SMA. Most intralobular alpha-SMA positive cells represent, if not all, perisinusoidal cells (PSCs) which are involved in intralobular fibrogenesis in various liver diseases.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of alpha-smooth muscle actin protein expression in adipose-derived stem cells

The objective of this work was to study the response of adipose-derived stem cells (ASCs) to exogenous biochemical stimulation, and the potential of ASCs to differentiate toward the smooth muscle cell (SMC) lineage. Immunofluorescence staining and Western blot analysis detected protein expression of the early SMC marker alpha-smooth muscle actin (alpha-SMA) in both control and experiment groups. Expression of alpha-SMA in ASCs significantly increased when treated with transforming growth factor-beta1, while alpha-SMA expression only slightly increased in the presence of retinoic acid (RA), beta-mercaptoethanol and ascorbic acid. Treatment with platelet-derived growth factor-BB, RA and dibutyryl-cyclic adenosine monophosphate decreased the expression of alpha-SMA significantly. While beta-mercaptoethanol and ascorbic acid, as well as RA have resulted in increased alpha-SMA expression in marrow-derived mesenchymal stem cells and other progenitor cells, our results demonstrate that these treatments do not significantly increase alpha-SMA expression, indicating that the differentiation potential of ASCs and mesenchymal stem cells may be fundamentally different.     

Characterization of transforming growth factor-beta 1 gene expression in porcine immune cells.

We have investigated the regulation of transforming growth factor beta 1 gene expression in a variety of porcine immune cell populations, including peripheral blood mononuclear cells (PBMC), peripheral blood monocytes, alveolar macrophages and lymphoid cells from various swine lymphoid tissues. Using porcine transforming growth factor beta 1 cDNA probes in Northern blot assays, messages of 2.5 and 3.5 kb TGF beta 1 mRNA were detected in the cells investigated. A variety of mitogenic and immunomodulatory substances were examined for their ability to induce TGF beta 1 mRNA expression. These include phorbol 12-myristate 13-acetate (PMA), phytohemagglutinin (PHA), concanavalin A (Con A), lipopolysaccharide (LPS), dexamethasone (Dex), tumor necrosis factor (TNF) and interleukin (IL)-1 alpha. While low level constitutive expression of TGF beta 1 mRNA was detected from all cells investigated, PMA treatment of PBMC and alveolar macrophages resulted in a more than 10-fold increase in the steady-state level of TGF beta 1 mRNA within 2 hr of PMA addition. Also, the effect of opiate drugs, methadone (Md) and morphine (Mor), on TGF beta 1 gene expression was determined. Cells treated with opiates expressed the same levels of TGF beta 1 mRNA as untreated cells. Since TGF beta 1 biological activity can be induced by opiates, the regulation of TGF beta 1 gene expression likely involves mechanisms that do not cause changes in mRNA levels.