Involvement of tyrosine kinase activity in the low-density lipoprotein receptor expression in human lung adenocarcinoma cell line A549

The effect of LDL particles on the behaviour of epithelial noncancer and cancer cell lines after in vitro induced injury

Cell spreading capability and cell proliferation are the major processes in wound healing of injured epithelia as well as in tumour progression. The effect of low-density lipoprotein (LDL) particles as a major extracellular source of cholesterol was evaluated in the re-epithelisation assay of in vitro induced injury. We selected two noncancer cell lines with different dependence on LDL concentrations, the kidney epithelial cells (MDCK) with higher dependence and keratinocytes (HaCaT) with lower dependence on LDL, and three cancer cell lines originating from epithelial cells: A549 (alveolar), CaCo-2 (intestinal) and RT4 (urothelial). All cells were incubated in a control medium, in an LDL-enriched medium or in an LDL-deficient medium. The LDL-enriched medium stimulated cell spreading of MDCK cells which, together with increased proliferation of these cells, resulted in an enhanced re-epithelisation of in vitro induced injury. LDL deficiency caused lower cell spreading which resulted in a decreased re-epithelisation despite the higher proliferation of MDCK cells in this medium. The re-epithelisation of keratinocytes (HaCaT) was not affected by altered LDL concentrations. In cancer cell lines A549, CaCo-2 and RT4, wide heterogeneity regarding cell proliferation and spreading capability was observed after treatment with different LDL concentrations. LDL had no influence on actin filament and tight junction distribution in any of the tested cell lines. The cholesterol content of all cell types, except for CaCo-2 cells, proved to be independent of the LDL level. Further research of the beneficial effects of LDL is needed to prove LDL as a safe enhancer of epithelial wound healing.

Low-density lipoprotein-bound aluminum sulfophthalocyanine: targeting tumor cells for photodynamic therapy

The aim of this study was to evaluate the role of low-density lipoproteins (LDLs) as a vehicle for aluminum sulfophthalocyanine ( AlPcS ) to target tumor cells for photodynamic therapy (PDT). LDLs are biological particles containing an apolipoprotein which recognizes with high affinity specific receptors on many cell types, including cancer cells. LDL was loaded with AlPcS in two different manners. In the first procedure, the tetrasulfonated AlPcS4was covalently bound to the protein part of the LDL via amide bonds to 6-carboxypentylaminosulfonyl spacer chains attached to two of the four sulfonate groups, i.e. AlPcS4A2. In the second procedure, the AlPcS4was substituted with a linear dodecylaminosulfonyl chain, i.e. AlPcS4( C12) and non-covalently inserted into the phospholipid monolayer of the LDL. Both preparations contained over 50 moles AlPcS /mole LDL. They were tested in vitro for their phototoxic properties against the EMT-6 mouse mammary tumor cell line and the A-549 human lung adenocarcinoma cell line. Cell survival was assessed using the MTT colorimetric assay. Association of the free AlPcS4( C12) with LDL increased the in vitro phototoxicity of the dye substantially against both cell lines while the covalently loaded AlPcS4A2-LDL preparation showed little cytotoxicity, even at a 10-fold-higher light or drug doses. It was postulated that the covalent labeling of the protein moiety with the Pc greatly reduced LDL receptor recognition, rendering this derivative photo-inactive. Photodynamic therapy of EMT-6 tumor-bearing mice showed that the free and LDL-associated AlPcS4( C12) exhibited similar activities, with 100% cure one week post-PDT at 0.2 μmol kg−1. We conclude that the attached aliphatic chain of the AlPcS4( C12) greatly enhances the phototoxicity of the parent AlPcS4but that pre-association of the AlPcS4( C12) with LDL does not further augment its in vivo photodynamic efficacy.

High folic acid increases cell turnover and lowers differentiation and iron content in human HT29 colon cancer cells

Folate, a water-soluble B vitamin, is a cofactor in one-carbon metabolism and is essential for DNA synthesis, amino acid interconversion, methylation and, consequently, normal cell growth. In animals with existing pre-neoplastic and neoplastic lesions, folic acid supplementation increases the tumour burden. To identify processes that are affected by increased folic acid levels, we compared HT29 human colon cancer cells exposed to a chronic supplemental (100 ng/ml) level of folic acid to cells exposed to a normal (10 ng/ml) level of folic acid, in the presence of vitamin B12and other micronutrients involved in the folate–methionine cycle. In addition to higher intracellular folate levels, HT29 cells at 100 ng folic acid/ml displayed faster growth and higher metabolic activity. cDNA microarray analysis indicated an effect on cell turnover and Fe metabolism. We fully confirmed these effects at the physiological level. At 100 ng/ml, cell assays showed higher proliferation and apoptosis, while gene expression analysis and a lower E-cadherin protein expression indicated decreased differentiation. These results are in agreement with the promoting effect of folic acid supplementation on established colorectal neoplasms. The lower expression of genes related to Fe metabolism at 100 ng folic acid/ml was confirmed by lower intracellular Fe levels in the cells exposed to folic acid at 100 ng/ml. This suggests an effect of folate on Fe metabolism.

Vegetables affect the expression of genes involved in carcinogenic and anticarcinogenic processes in the lungs of female C57BL/6 mice

Worldwide, lung cancer is the most prevalent and lethal malignant disease. In addition to avoidance of the most predominant risk factor, i.e., tobacco use, consumption of high amounts of vegetables and fruits could be an effective means of preventing lung cancer. However, the molecular mechanisms underlying lung cancer risk reduction by vegetables are not clear. In the present study, the effect of vegetables on gene expression changes in the lungs of female C57Bl/6 mice was investigated using cDNA microarray technology. The mice were fed 1 of 8 diets for 2 wk: a control diet containing no vegetables (diet 1); a diet containing a vegetable mixture at 100 (diet 2, 10% dose), 200 (diet 3, 20% dose), or 400 (diet 4, 40% dose) g/kg; or a diet containing cauliflower at 70 (diet 5, 7% dose); carrots at 73 (diet 6, 7.3% dose); peas at 226 (diet 7, 22.6% dose); or onions at 31 (diet 8, 3.1% dose) g/kg. The vegetable mixture consisted of these 4 individual vegetables. After the mice were killed, the lungs were removed and total RNA was isolated from the lungs for expression analysis of 602 genes involved in pathways of (anti)-carcinogenesis. The results of this study suggest that individual vegetables have a higher potential of modulating genes (5 from the 8 modulated genes) in favor of lung cancer risk prevention, in comparison with the vegetable mixture (2 from the 7 modulated genes); the other gene modulations are expected to enhance lung cancer risk. The pathways involved were miscellaneous and included cell growth, apoptosis, biotransformation, and immune response. Furthermore, carrots were able to modulate most gene expressions, and most of these effects occurred in processes that favored lung cancer risk prevention. The current study provides more insight into the genetic mechanisms by which vegetables, in particular carrots, can prevent lung cancer risk.

Tyrosine kinase-dependent modulation of 3-hydroxy-3-methylglutaryl-CoA reductase in human breast adenocarcinoma SKBR-3 cells

3-Hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase is the major rate-limiting enzyme in sterol and non-sterol isoprenoid synthesis. Isoprenoids are involved in the mechanisms of cell proliferation and transformation leading notably to crucial post-translational maturation of small G-proteins of the Ras superfamily. HMG-CoA reductase is among the most highly regulated enzymes. It is controlled by several feedback regulation mechanisms induced by sterol and non-sterol metabolites. The present results show that tyrosine kinase activity is also involved in the regulation of HMG-CoA reductase activity in the human breast cancer cell line SKBR-3. Incubation of SKBR-3 cells with the tyrosine kinase inhibitor, herbimycin A, induces a concentration-dependent reduction of HMG-CoA reductase activity with an IC50 of 80nM. The inhibition of HMG-CoA reductase activity by herbimycin A is also time-dependent. A similar effect of herbimycin A was obtained on the steady-state level of the HMG-CoA reductase protein. The effect of herbimycin A is probably specific as it abolished the stimulation of reductase activity by epidermal growth factor. To elucidate the molecular basis of the inhibition of HMG-CoA reductase activity and protein level by herbimycin A, we performed experiments to study the metabolic turnover of this enzyme using [35S]methionine and [35]cysteine. Herbimycin A (1 microM) did not have any significant effect on the rate of HMG-CoA reductase protein degradation but did affect its rate of synthesis and mRNA levels. The decrease in protein synthesis rate correlates with the lower reductase protein level but is more pronounced than the decrease in mRNA levels. Taken together, the results reveal a novel pathway of regulation of HMG-CoA reductase expression and activity by cellular tyrosine kinase activities.