Response of FR3T3 cells transformed by Ha-ras oncogene and epidermal growth factor gene to differentiation induction by N,N-dimethylformamide

Inhibitory effect of 1-O (2 methoxy) hexadecyl glycerol and phenylbutyrate on the malignant properties of human prostate cancer cells

The ability of the naturally occurring ether lipid, 1-O (2 methoxy) hexadecyl glycerol (MHG), and phenylbutyrate (BP) to inhibit cellular proliferation, anchorage-independent growth and cellular invasion in the human prostate cancer LnCap and DU145 cells was determined. Both MHG and PB inhibited the malignant properties of these prostate cancer cells. The concentrations required to achieve similar inhibitory effect, however, were significantly different for these two agents. MHG inhibited cell growth with equal potency in these cell lines with an IC-50 value of 93 microM for LnCap, and 97 microM for DU145. The IC-50 values for PB were 1.3 mM and 7.3 mM, respectively, for LnCap and DU145 cells. Both MHG and PB (IC-50 concentrations) inhibited the anchorage-independent growth and cellular invasion in these cells. Over 50% inhibition of anchorage-independent growth was achieved for both LnCap and DU145 cells by PB, while a lesser degree of inhibition was achieved with MHG. Both MHG- and PB-treated cells showed a reduced propensity to invade matrigels. Invasion of PB-treated LnCap and DU145 cells was reduced, respectively, by approximate 41 and 30% when compared to untreated control cells, while invasion of MHG-treated LnCap and DU145 cells was reduced to a lesser extent. Because differentiation-inducing agents may possess chemopreventive properties, the use of naturally occurring MHG and nontoxic PB in the chemoprevention of malignant diseases warrants further investigation.

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.

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.

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.

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.