Differentiation-promoting effect of 1-O (2 methoxy) hexadecyl glycerol in human colon cancer cells

Alkylglycerols are naturally occurring bioactive ether lipids found in great abundance in the livers of many marine species. In this study, we evaluated the differentiation-promoting potential of a methoxy substituted alkylglycerol--1-O (2 methoxy) hexadecyl glycerol (MHG)--to promote a more benign or differentiated phenotype in human colon cancer cells. Three cell lines with different biological and phenotypic properties were used. They were the moderately differentiated and growth factor-responsive Moser, the growth factor-unresponsive and malignant HT29, and the poorly differentiated and growth factor-unresponsive HCT116. Treatment of these cell lines with MHG resulted in a downmodulation of cellular proliferation, a reduced propensity for anchorage-independent growth, and a reduced capacity in cellular invasion. Induction of the colon-associated and differentiation-related molecule carcinoembryonic antigen was also observed in the three cell lines. Induction of the transformation-sensitive and differentiation-related glycoprotein fibronectin was observed in the HT29 cells. It is concluded that MHG was biologically active and promoted a more benign or differentiated phenotype in these colon cancer cells. Since differentiation-inducing agents may possess chemoprevention properties, the use of MHG and the alkylglycerols in inducing differentiation or in chemoprevention of malignant diseases warrants further investigation.

Differentiation-inducing effect of retinoic acid, difluoromethylornithine, sodium butyrate and sodium suramin in human colon cancer cells

We investigated the relative effectiveness of four differentiation-inducing chemicals to induce a more normal or benign phenotype in the human colon cancer cell lines Moser and HT29. The differentiation-inducing capability of all-trans retinoic acid (ATRA), difluoromethylornithine (DFMO), sodium butyrate (NaB) and sodium suramin (NaS) was evaluated in terms of the efficacy of these chemicals in inhibiting cellular proliferation, growth in soft agarose, invasion of matrigel and induction of morphological alteration. The relative ability of these chemicals to induce production of the differentiation-related molecules fibronectin and carcinoembryonic antigen was also determined. Overall, ATRA was found to be the most effective chemical in inducing differentiation as measured by these parameters. The Moser cells were more susceptible to differentiation induction by comparison with the HT29 cells. Both similarities and differences in the cellular responses to DFMO, NaB and NaS were also observed for the Moser and HT29 cells. The differences in cellular responses to these chemicals may be due to different phenotypic properties of these two cell lines and different mechanisms of action of these chemicals.

Epidermal growth factor receptor (EGFR) antisense transfection reduces the expression of EGFR and suppresses the malignant phenotype of a human ovarian cancer cell line

An EGFR-expressing clone of the human ovarian cancer line 2774 was transfected with an antisense construct of EGFR to test how suppression of this gene modulates the malignant phenotype. Transfected clones were screened for EGFR expression by Western blot and FACS analysis. Anchorage-independent growth was used to assess the effect of reduced EGFR on the malignant behavior of the cells. Several transfected clones with decreased EGFR (40-50% reduction) were identified. A correlation was noted between reduced EGFR and decreased anchorage-independent growth, with the transfected clones losing the ability to grow in agarose and responsiveness to exogenous EGF. These results suggest that EGFR may be an important factor in the malignant behavior of this ovarian cancer cell line.

Inhibition of human colon cancer malignant cell behavior and growth by antisense epidermal growth factor receptor expression vector

Human colon cancer cells utilize the epidermal growth factor (EGF) family of growth factors and the receptor for these growth factors (EGFR) in sustaining their malignant phenotype. Disrupting EGFR expression by expressing antisense EGFR RNA (through transfection with an appropriate antisense EGFR expression vector under metallothionein promoter control) downregulated the malignant behavior of human colon cancer Moser cells and blocked the ability of exogenous EGF in stimulating malignant cell behavior. The antiproliferative effect of antisense EGFR expression vector was determined in three human colon cancer cell lines (Moser, HCT116 and HT29 possessing different biological properties and rate of proliferation) in an in vitro therapeutic setting using an antisense EGFR expression vector under the control of a viral promoter. Different degree of inhibition was achieved for each cell line after one dose of antisense treatment. The differences in the antiproliferative effect observed may be due to differences in the rate of proliferation and/or recovery from antisense effect, and the differences in transfection efficiency among the cell lines.

mdm2-P2 transcript levels predict the functional activity of the p53 tumor suppressor in primary leukemic cells

The mdm2-P2 promoter is a transcriptional target of the p53 tumor suppressor. The aim of this study was to determine if there is an association between the level of these transcripts and the status of the p53 gene in human leukemic cells. A correlation between mdm2-P2 transcript levels and p53 gene status was observed in all cell lines examined. Primary malignant cells from 10 leukemic patients were also analysed for both mdm2-P2 levels and p53 gene status. All five patients with detectable mdm2-P2 transcripts possessed wild-type p53 alleles. However, only two of five patients with undetectable mdm2-P2 transcripts possessed mutant p53. mdm2-P2 levels were also determined in primary leukemic cells from 14 additional cases both before and after in vitro exposure to cisplatin. The p53 gene was found to be wild-type in all cases where mdm2-P2 levels were induced by cisplatin. There were four cases where no, or only modest, increases in mdm2-P2 levels were detected after cisplatin exposure. Two of these patients were found to harbor mutant p53 while one other possessed leukemic cells with elevated levels of mdm2 protein. These results show that induction of mdm2-P2 transcripts can be used to predict the presence of transcriptionally active p53 in primary leukemic cells.

Protein kinase Calpha controls the adhesion but not the antiproliferative response of human colon carcinoma cells to transforming growth factor beta1: identification of two distinct branches of post-protein kinase Calpha adhesion signal pathway

Transforming growth factor beta1 (TGFbeta1) inhibits cellular proliferation and induces the expression of the matrix adhesion molecules fibronectin (FN) and laminin (LM) in a concurrent manner, followed by the induction of the intercellular adhesion molecule carcinoembryonic antigen (CEA) (collectively designated as adhesion responses) in TGFbeta1-responsive human colon carcinoma cells. Exactly how TGFbeta1 controls cellular adhesion and proliferation is poorly understood. In the present report, we showed that down-regulating protein kinase Calpha (PKCalpha) expression blocked the induction of these adhesion responses by TGFbeta1, showing that PKCalpha is a postreceptor focal point controlling the induction of these molecules. Down-regulating PKCalpha expression, however, had minimal effect on the antiproliferative response to TGFbeta1 or the induction of p21/WAF1, a marker associated with the antiproliferative effect of TGFbeta1, demonstrating that the adhesion signal pathway is distinct from that of antiproliferation. Blockade of FN induction blocked the induction of CEA but not the induction of LM. Blockade of LM induction, on the other hand, had no effect on the induction of FN and CEA. These results established the existence of two distinct and parallel postPKCalpha adhesion signal pathways, one leading to the induction of LM and the other leading to the induction of FN and CEA.

Modulation of cellular proliferation and production of prostate-specific antigen and matrix adhesion molecules in human prostate carcinoma cells by polypeptide growth factors: comparative analyses of MDA PCa2a with established cell lines

The cellular responses of a newly established and early-passage human prostate adenocarcinoma cell line, MDA PCa2a, to transforming growth factor (TGF) beta1, epidermal growth factor (EGF), and TGFalpha were characterized in terms of proliferation, production of prostate-specific antigen (PSA), fibronectin (FN) and laminin (LM). The responses of the MDA PCa2a cells were compared with those of the well-established human prostate carcinoma cell lines LNCap, PC3, and DU145. The MDA PCa2a cells were more responsive to the growth-inhibitory effect of TGFbeta1 than the established cell lines. The androgen-responsive cell lines (MDA PCa2a and LNCap) were relatively responsive to the growth-stimulatory effect of EGF and TGFalpha whereas the androgen-independent lines (PC3 and DU145) were not. Only the androgen-responsive cells produced PSA, which was further upregulated by treatment with growth factors. The androgen-independent cells did not produce PSA, and growth factors had no effect on PSA production. However, all cell lines produced abundant amounts of FN and LM, and the levels of production of these molecules were subject to modulation by growth factors. It is concluded that each growth factor elicits diverse and distinct responses in prostate carcinoma cells, which may reflect the involvement of diverse post-receptor signal pathways.

Evoked excitability changes at the terminals of midlumbar premotor interneurons in the cat spinal cord

We present evidence that the electrical excitability of the terminals of a group of spinal premotor interneurons can be increased after stimulation of sensory afferents. The interneurons were located in the midlumbar segments of the spinal cord and had projections to the lower lumbar motor nuclei. Thresholds for antidromic activation of a substantial number of interneurons were reduced after electrical stimulation of group II muscle afferents. Several observations suggest that the excitability changes are unlikely to have arisen from electrotonic spread of depolarization from the interneuron soma to its terminals or by environmental changes in the vicinity of the terminals related to neuronal activity. A particularly interesting possibility is that the excitability of the central terminals of the interneurons is increased because they are depolarized by a mechanism similar to that acting at the terminals of primary sensory afferents (primary afferent depolarization, PAD), which accompanies one type of presynaptic inhibition. This type of presynaptic action has been shown in premotor interneurons in the lamprey but not in the mammalian spinal cord. From our observations the organization of the systems generating excitability changes at the interneuron terminals seem in general to parallel the organization of the systems generating PAD at afferent terminals, raising the possibility that common principles might underlie the operation of this form of presynaptic control.

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.