Control of fibronectin receptor expression by fibronectin: Antisense fibronectin RNA downmodulates the induction of fibronectin receptor by transforming growth factor β1

The results of our previous studies of mouse embryo fibroblasts showed that fibronectin expression and fibronectin receptor expression are tightly coregulated and that fibronectin modulates expression of its receptor in response to treatment with the differentiation-inducing agent N,N,-dimethylformamide (Varani and Chakrabarty, 1990, J. Cell. Physiol., 143:445-454; Huang et al., 1994, J. Cell. Physiol., 161:470-482). We also found that transforming growth factor beta1 (TGFbeta1) induces a more differentiated phenotype in the epithelium-derived human colon carcinoma cell line Moser and upregulates the expression of both fibronectin and its receptor (Huang and Chakrabarty, 1994, Int. J. Cancer, 57:742-746). By expressing antisense fibronectin RNA in Moser cells, we have downregulated fibronectin mRNA expression and thus blocked the ability of TGFbeta1 to induce fibronectin expression (Huang and Chakrabarty, 1994, J. Biol. Chem., 269:28764-28768). In this study, we examined the effect of antisense fibronectin RNA expression on the induction of fibronectin receptor by TGFbeta1 and tested the hypothesis that the induction of fibronectin expression by TGFbeta1 is required for the induction of fibronectin receptor expression. Blocking fibronectin induction by TGFbeta1 attenuated the ability of TGFbeta1 to upregulate the expression of cell-surface fibronectin receptors, alpha5beta1 integrin expression, and adhesion to extracellular matrix fibronectin. We therefore conclude that induction of fibronectin expression is required for optimal upregulation of fibronectin receptor expression by TGFbeta1.

Modulation of chemosensitivity in human colon carcinoma cells by downregulating protein kinase C alpha expression

Protein kinase C (PKC) is thought to play a role in tumor progression and drug resistance of colon carcinomas. Specifically, the PKC alpha isoform has been implicated in drug resistance and responsiveness of colon carcinoma cells to growth factors. Therefore, in this study we determined the effect of downregulating PKC alpha expression by transfecting human colon carcinoma cells with an antisense PKC alpha expression vector and then determined the sensitivity of these cells to the anticancer drugs mitomycin C (MMC), 5-fluorouracil (5-FU) and vincristine (Vin). Transiently transfecting the human colon carcinoma cell lines Moser, SW480 and HT29 with antisense PKC alpha expression vector (but not antisense PKC beta expression vector) consistently increased the sensitivity of these cells to MMC, 5-FU and VIN by several-fold. Sensitivity to these drugs was then further determined in the Moser colon carcinoma cell line stably transfected with antisense PKC alpha expression vector. This stably transfected cell line, which expressed a high level of antisense PKC alpha RNA with a concurrent reduction of PKC alpha protein expression, was found to exhibit an increased sensitivity to these anticancer drugs. Thus, strategies designed to downregulate PKC alpha expression may have potential in improving the responses of colon carcinoma cells to cytotoxic drugs.

Epidermal growth factor expression in human colon and colon carcinomas: anti-sense epidermal growth factor receptor RNA down-regulates the proliferation of human colon cancer cells

Human colon cancer cell lines express epidermal growth factor (EGF) mRNA, secrete EGF and may respond to it via the cell-surface EGF receptor (EGFR). Expression of these molecules in human colon and colon tumor, however, is not clear. Reverse transcription-polymerase chain reaction (RT-PCR) analyses of RNA prepared from paired normal human colon and colon tumor samples from 12 individuals followed by Southern blotting analyses of the RT-PCR products revealed a major fragment of 527 bp and a minor fragment of 404 bp that hybridized to a human EGF cDNA probe under stringent conditions. Identical results were obtained from 8 human colon cancer cell lines. Cloning and sequencing of PCR products confirmed that both fragments were from the human EGF gene; the 527-bp fragment corresponded exactly to nucleotides 2,891 to 3,417 of the human EGF mRNA reported by others. A deletion of 123 nucleotides (nucleotides 3,172 to 3,294) was found in the 404-bp fragment. Immunohistochemical studies using cyostat sections of human colon specimens showed that EGF was expressed in the human colon and that expression was restricted to the epithelial colonic crypt cells and epithelium-derived cancer cells. Since EGF and EGF-related molecules are potent mitogens that mediated their effect through the EGFR, we also determined the efficacy of anti-sense EGFR RNA in circumventing the EGFR-related pathway of proliferation. Expression of anti-sense EGFR RNA, by transfection with an inducible anti-sense EGFR expression vector, down-regulated cell-surface EGFR expression and proliferation of these cells and their ability to grow in soft agar. Anti-sense EGFR RNA was found to be an anti-proliferative agent in both relatively non-aggressive and highly aggressive human colon cancer cells.

Role of protein kinase C alpha in the induction of carcinoembryonic antigen by transforming growth factor beta 1

Previous studies showed that transforming growth factor beta 1 (TGF beta 1) regulates the expression of carcinoembryonic antigen (CEA) and CEA-cross-reactive glycoproteins (CEA-GLYs) in human colon carcinoma cells through a signal-transducing pathway associated with protein kinase C (PKC) (Chakrabarty, J. Cell. Physiol., 1992, 152:494-499). In this study we determined the role of the PKC alpha isoform in the regulation of CEA and CEA-GLYs expression by TGF beta 1. Expression of PKC alpha antisense RNA, through transfection experiments with an antisense PKC alpha expression vector, resulted in down-modulation of PKC alpha RNA and protein expression. TGF beta 1 was unable to stimulate the expression and secretion of CEA in cells in which the expression of PKC alpha protein was substantially reduced. The ability of TGF beta 1 to stimulate the expression of the 95- and 55-kDa CEA-GLYs, however, was not affected. We therefore conclude that TGF beta 1 regulates the secretion and expression of CEA through a signal-transducing pathway associated with PKC alpha. TGF beta 1 may also regulate the expression of CEA-GLYs through signal-transducing pathways associated with other PKC isoforms.

Expression of antisense epidermal growth factor receptor RNA downmodulates the malignant behavior of human colon cancer cells

Human colon cancer (Moser) cells produce and secrete epidermal growth factor (EGF) and respond to EGF via an autocrine/paracrine mode through the cell surface EGF receptor (EGFR). In this report we show that EGF promotes the malignant behavior of the Moser cells in vitro in terms of growth in soft agarose and invasion of Matrigel-coated porous membranes. Expressing antisense EGFR RNA in the Moser cells (through transfection with an inducible antisense EGFR expression vector) downmodulated the expression of cell surface EGFR and EGFR mRNA with a concurrent inhibition of growth in soft agarose and invasion of Matrigel-coated membranes. In addition, the ability of exogenously applied EGF in promoting the malignant behavior of these cells was circumvented. We conclude that antisense EGFR RNA was a potent agent in circumventing the in vitro malignant properties of the Moser cells.

Serum levels of transforming growth factor alpha in gastrointestinal cancer patients

Transforming growth factor alpha (TGF alpha), a polypeptide growth-stimulating factor, has been implicated to play a role in the progression of gastrointestinal (GI) cancer. It has been suggested that TGF alpha expression in tumors or TGF alpha in the biological fluids of cancer patients may have tumor marker value. The serum levels of TGF alpha in GI cancer patients have not been reported. In this study, the serum TGF alpha levels of 100 GI cancer patients, as well as 74 healthy individuals, were determined by a TGF alpha-specific RIA kit. All of the cancer patient sera and 67% of the normal sera had detectable levels of TGF alpha. The TGF alpha concentrations in GI cancer patients ranged from 119 to 760 pg/ml, with a mean value of 269 +/- 102 pg/ml. Fifty normal individuals had detectable levels of TGF alpha, and their levels ranged from 120 to 207 pg/ml, with a mean value of 147 +/- 18 pg/ml. Differences in serum TGF alpha concentration between cancer patients and healthy individuals were found to be statistically significant, as evaluated by Mann-Whitney and Student's t tests. Serum TGF alpha levels were found to be significantly elevated in all disease stages of gastric, pancreas, colon, and rectal cancers, and only in the late stages of esophageal cancer. Serum carcinoembryonic antigen levels were significantly elevated only in the late stages of these diseases. The potential of serum TGF alpha as a tumor marker for GI malignancy, therefore, warrants further investigation.

Control of AKR fibroblast phenotype by fibronectin: regulation of cell-surface fibronectin binding receptor by fibronectin

Results of previous studies show that the expression of fibronectin and its cell-surface fibronectin binding receptor is coregulated in 3-methylchloranthrene transformation of normal AKR-2B cells to form AKR-MCA cells and in N,N,-dimethylformamide (DMF) induction of differentiation of transformed AKR-MCA cells (1990, J. Cell. Physiol., 143:445). In this study, we tested the coregulation hypothesis by transfection experiments using an antisense fibronectin expression vector. We determined the effect of antisense fibronectin RNA expression on untransformed AKR-2B cells, and on the responses of transformed AKR-MCA cells to DMF treatment. Expression of antisense fibronectin RNA in AKR-2B cells down-modulated fibronectin production, reduced adhesion to extracellular fibronectin, and altered cellular morphology. Saturation binding and Scatchard analyses using radiolabelled fibronectin revealed a concurrent down-modulation of cell-surface fibronectin binding sites, but the binding affinity of the receptor for the ligand was not affected. Immunoblotting and immunostaining revealed down-modulation of the expression of alpha 5 beta 1 integrins. Expression of antisense fibronectin RNA in AKR-MCA cells down-modulated the ability of DMF to restore normal fibronectin production, cell-surface fibronectin binding receptor, adhesion to extracellular fibronectin, and cellular morphology. These studies show that both fibronectin and its cell-surface fibronectin binding receptor were tightly regulated during transformation and induction of differentiation in these cells, that the ligand and its cell-surface fibronectin binding receptor worked together to bring about phenotypic changes, and that fibronectin production regulated the expression of its cell-surface fibronectin binding receptor.

Expression of antisense fibronectin RNA in human colon carcinoma cells disrupts the regulation of carcinoembryonic antigen by transforming growth factor beta 1

Transforming growth factor beta 1 regulates the expression of extracellular matrix adhesion molecules and the carcinoembryonic antigen gene family of glycoproteins in the Moser colon carcinoma cell line. Expression of fibronectin antisense RNA in the Moser cells down-regulated fibronectin mRNA expression and blocked the ability of transforming growth factor beta 1 to stimulate fibronectin secretion. Cells expressing antisense fibronectin RNA exhibited a higher rate of proliferation, changed their morphology, and produced more laminin in response to treatment with transforming growth factor beta 1. The stimulation of carcinoembryonic antigen secretion by transforming growth factor beta 1 (which normally lagged 10-16 h behind that of fibronectin secretion stimulated by transforming growth factor beta 1) was blocked by the expression of antisense fibronectin RNA. Thus, the stimulation of fibronectin secretion by transforming growth factor beta 1 was a prerequisite for subsequent stimulation of carcinoembryonic antigen secretion. In addition, the stimulation of the cellular expression of carcinoembryonic antigen and three carcinoembryonic antigen cross-reactive species of glycoproteins by transforming growth factor beta 1 was down-modulated in cells expressing antisense fibronectin RNA. We therefore conclude that fibronectin may play an important role in the mechanisms of transforming growth factor beta 1 regulation of the expression of carcino-embryonic antigen gene family of glycoproteins.

Regulation of fibronectin and laminin receptor expression, fibronectin and laminin secretion in human colon cancer cells by transforming growth factor-beta 1

Transforming growth factor (TGF)-beta 1 modulates the expression of extracellular matrix (ECM) glycoproteins, fibronectin and laminin and the adhesion of Moser colon cancer cells to these glycoproteins. Since adhesion can be altered through expression of cell-surface receptors, binding affinities of adhesion molecules for receptors, or both, we investigated the effect of TGF-beta 1 on the binding properties of fibronectin and laminin to their cell-surface receptors by saturation binding and Scatchard analyses using radiolabeled fibronectin and laminin. Fibronectin bound to its cell-surface receptor with high affinity (Kd = 1.25 x 10(-9) M), Moser cells had approximately 7.1 x 10(4) fibronectin-binding sites per cell. TGF-beta 1 treatment rapidly up-modulated the number of cell-surface fibronectin-binding sites by 1.9-fold. The binding affinity of fibronectin for the receptor, however, was not altered. Laminin was found to bind to a higher-affinity and a lower-affinity receptor. Moser cells expressed approximately 1.1 x 10(3) higher-affinity laminin-binding sites and approximately 3.1 x 10(4) lower-affinity-binding sites per cell. TGF-beta 1 rapidly increased the expression of the higher-affinity sites 3-fold and the lower-affinity sites 5-fold. The binding affinity of both the higher-affinity and lower-affinity laminin receptors increased 3-fold after 2 and 6 hr of TGF-beta 1 treatment respectively. Concurrent with receptor modulation, TGF-beta 1 induced the secretion of fibronectin and laminin from Moser cells. Northern hybridization analyses showed a concurrent stimulation of the expression of the mRNAs for ligands (fibronectin and laminin) and the mRNAs for the integrin species of the fibronectin and laminin receptors (alpha 5 and alpha 6 subunits). Thus the production of fibronectin and laminin and the expression of their receptors were tightly co-regulated by TGF-beta 1.

Elevated serum levels of transforming growth factor-alpha in breast cancer patients

Previous studies suggest that transforming growth factor-alpha (TGF alpha) may have the potential of a tumor marker. Since the levels of serum TGF alpha in cancer patients and healthy individuals have not been reported, we determined the serum TGF alpha levels of 83 breast cancer patients and 74 healthy individuals by using a TGF alpha radioimmunoassay kit. All of the cancer patients' sera were positive for TGF alpha; their TGF alpha concentrations ranged from 210 to 740 pg/ml, with a mean of 353 +/- 98 pg/ml. Sixty-seven percent (50 cases) of normal sera were positive for TGF alpha; the levels ranged from 120 to 207 pg/ml, with a mean of 144 +/- 17 pg/ml. The difference in serum TGF alpha levels between cancer patients of different disease stages and healthy individuals was found to be statistically significant by Student t-test and the Mann-Whitney test. No correlation was found between serum carcinoembryonic antigen and TGF alpha levels. The potential of serum immunoreactive TGF alpha as a marker for breast cancer warrants further investigation.

Effects of streptokinase on infarct size in rabbits in the presence and absence of coronary artery recanalization

Despite variable efficacy in achieving recanalization, different thrombolytic agents demonstrate similar abilities to reduce mortality following myocardial infarction. We investigated whether factors other than the ability to achieve coronary artery recanalization are important in mediating the beneficial effects associated with thrombolytic therapy during acute myocardial infarction using anaesthetized rabbits. Coronary artery occlusion was produced using either a single ligature (which was released to initiate reperfusion) or by placing two ligatures 5 mm apart to allow the formation of an intraluminal thrombus. In this case, ligature removal followed by thrombolysis was required for recanalization to occur. Experiments were performed in the presence and absence of streptokinase. Streptokinase was most effective in reducing myocardial necrosis when associated with thrombolytic recanalization (total left ventricular infarct size was reduced from 37 +/- 7% to 13 +/- 1%, P < 0.01). However, streptokinase also reduced infarct size in the absence of reperfusion (45 +/- 4% vs 35 +/- 2%, P < 0.05), although further work is needed to clarify the mechanisms.

Proliferation of human colon cancer cells: role of epidermal growth factor and transforming growth factor alpha

Human colon cancer cells produce and secrete a variety of polypeptide growth factors. The functional role of these growth factors, however, is poorly understood. Though the secretion of epidermal growth factor (EGF)-like activity and EGF-related molecules by human colon cancer cells in culture has been reported, it is not known whether colon cancer cells produce and secrete EGF, and the functional role of EGF in the growth control of these cells is also unknown. We have shown that EGF acts as a potent growth stimulator on the moderately differentiated Moser colon cancer cell line and as an inhibitor on the highly metastatic KM12SM cell line. In the present study, we show that EGF is produced by human colon cancer cells and characterize the levels of EGF mRNA expression and EGF protein secretion from 8 human colon cancer cell lines. The cell-surface EGF receptors on these cell lines were also characterized by radiolabeled ligand binding and Scatchard analyses. All the cell lines expressed EGF mRNA and secreted EGF. Both high- and low-affinity subtypes of EGF receptor were detected on 7 of the cell lines. These lines also secreted transforming growth factor (TGF)alpha. Some cell lines exhibited a proliferative response to treatment with either exogenous EGF or TGF alpha, while others did not respond to treatment with these growth factors. Antibody-blocking experiments, using anti-EGF or anti-EGF receptor antibody, suggested that these cell lines could be broadly classified into 2 groups in terms of their autocrine or paracrine growth regulation via the cell-surface EGF receptor: (1) cells that utilized EGF and/or TGF alpha; and (2) cells that did not utilize EGF or TGF alpha (via the cell-surface receptor), even though they secreted abundant amounts of these growth factors.

Effects of cicletanine on haemodynamics, arrhythmias and extent of necrosis during coronary ligation in rabbits

1. The effects of cicletanine on arrhythmias, haemodynamics and extent of necrosis during myocardial ischaemia were investigated in rabbits subjected to coronary ligation. 2. Cicletanine increased cardiac output prior to coronary occlusion (P < 0.01) but had no other significant haemodynamic effects at this time and did not significantly alter heart rate, blood pressure or cardiac output during 30 min of ischaemia or 30 min of reperfusion. 3. Ventricular fibrillation and mortality were greater in control (65% and 60% respectively) than treated animals (15.4% and 15.4%, P < 0.01). 4. The extent of myocardial necrosis expressed as a percentage of the area at risk was also reduced by cicletanine from 61 +/- 8% in controls to 37 +/- 6% (P < 0.05). 5. These findings indicate that cicletanine attenuates arrhythmias and preserves myocardium in the early phase of ischaemia and this effect appears to be independent of an established antihypertensive action.

Effects of the PAF antagonists BN50726 and BN50739 on arrhythmogenesis and extent of necrosis during myocardial ischaemia/reperfusion in rabbits

1. The effects of two novel platelet activating factor (PAF) antagonists BN50726 and BN50739 on arrhythmias, haemodynamics and extent of necrosis during myocardial ischaemia and reperfusion were investigated in anaesthetized rabbits subjected to coronary artery ligation. 2. BN50739 reduced heart rate prior to coronary artery occlusion (P < 0.005) but had no other significant haemodynamic effects at this time. BN50739 and BN50726 did not significantly alter heart rate or blood pressure during 30 min of ischaemia or 30 min of reperfusion, compared to control hearts. 3. BN50739 and BN50726 had no effect on the incidence of arrhythmias during ischaemia. BN50726 significantly reduced the incidence of reperfusion ventricular fibrillation compared to controls (0% v 40%, P < 0.05), and improved survival (80% v 39%, P < 0.05). Similar trends were observed with BN50739. 4. BN50726 reduced the extent of necrosis compared to control hearts (18 +/- 2% v 30 +/- 3%, P < 0.01). A similar trend was observed with BN50739. 5. These results demonstrate that PAF antagonism with BN50726 attenuates reperfusion-induced arrhythmias and preserves myocardium in the early phase of ischaemia, independently of haemodynamic effects.

Role of protein kinase C in transforming growth factor-beta 1 induction of carcinoembryonic antigen in human colon carcinoma cells

Transforming growth factor-beta 1 (TGF-beta 1) regulates the expression of the carcinoembryonic antigen (CEA) gene family in the human colon carcinoma cell line Moser. The mechanisms through which it acts, however, are unknown. In this communication, several lines of evidence are presented to show that the induction of CEA expression and secretion (collectively called CEA responses) by TGF-beta 1 is associated with protein kinase C (PKC) pathway of signal transduction. Treatment of intact cells with the PKC-specific inhibitor calphostin C down-modulated cellular PKC phosphotransferase activity and blocked the induction of the CEA responses by TGF-beta 1. Depletion of PKC by treatment of intact cells with phorbol ester also blocked the action of TGF-beta 1. The induction of the CEA responses by TGF-beta 1 was also blocked by the protein kinase inhibitor 1-(isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), which also inhibited cellular PKC activity. However, TGF-beta 1 did induce the CEA responses in intact cells treated with the calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7), the calmodulin-dependent phosphodiesterase inhibitor calmidazolium, the diacylglycerol kinase inhibitor R59 022, and the G-protein inhibitors cholera toxin and pertussis toxin. Treatment of intact cells with TGF-beta 1 induced a rapid and transient increase in PKC phosphotransferase activity. TGF-beta 1, however, was unable to induce PKC enzymatic activity in cells pretreated with calphostin C. Therefore, it is concluded that TGF-beta 1 regulates the CEA responses through a signal transducing pathway associated with PKC.

Protective role of ascorbic acid against lipid peroxidation and myocardial injury

Ascorbic acid (AH2) is a potential scavenger of superoxide radical and singlet oxygen. In the guinea pig, marginal AH2 deficiency results in intracellular oxidative damage in the cardiac tissue as evidenced by lipid peroxidation, formation of fluorescent pigment and loss of structural integrity of the microsomal membranes. The oxidative damage does not occur due to lack of enzymatic scavengers of reactive oxygen species such as superoxide dismutase, catalase and glutathione peroxidase. Also, glutathione transferase activity is not decreased in AH2 deficiency. Lipid peroxidation, fluorescent pigment formation and protein modification disappear after AH2 therapy. These results, if extra-polated to human beings, would indicate that chronic subclinical AH2 deficiency may result in progressive oxidative damage which in the long run may lead to permanent degenerative diseases in the heart.