Oxidized LDL promotes vascular endothelial cell pinocytosis via a prooxidation mechanism.

Human low density lipoprotein (LDL) is prepared in the presence of antioxidants and is oxidized to different levels (measured by thiobarbituric acid reactive substance) with copper ion. The effects of unoxidized LDL and oxidized LDL (ox-LDL) on stress fiber formation, cell membrane ruffling, and pinocytosis (measured by [14C]sucrose uptake) in cultured human umbilical cord vein endothelial cells (EC) are compared. We show that at a concentration range of 100 to 200 microg cholesterol/ml, both unoxidized LDL and ox-LDL promote EC elongation and stress fiber formation, but the effect by the latter is more prominent when compared at the same dose range. In addition, ox-LDL also induces EC membrane ruffling and promotes pinocytosis. These effects are positively correlated with the extent of LDL oxidation and depend on the dose of ox-LDL. Ox-LDL-promoted membrane ruffling and pinocytosis are effectively blocked by brief preexposure of the cells to antioxidants. In contrast, stress fiber formation is not affected by antioxidant pretreatment. Although unoxidized LDL also promotes [14C]sucrose uptake, it is less potent than ox-LDL and significantly higher concentrations are required to produce a detectable effect. Unlike ox-LDL, unoxidized LDL-enhanced pinocytosis is not accompanied by the appearance of membrane ruffling; therefore, they may act via different mechanisms. Elevated pinocytosis may increase transcytotic activity of the endothelium, leading to an increased influx of plasma components such as LDL into the subendothelial space.

Retinoic Acid Modulates Epidermal Growth Factor Receptor Expression in Human Lung Epithelial Cancer Cells.

In human lung epithelial cancer cell line H460, an accumulation of epidermal growth factor receptors (EGF-R) was observed following treatment with 1 &mgr;M retinoic acid. An increae in (125)I-labeled EGF binding capacity was detected, which reached its highest level after 48 h of incubation with retinoic acid. Transiently increased autophosphorylation of EGF-R after 48 h of retinoic acid treatment correlated with enhancement of EGF binding capacity on the H460 cell surface. Nuclear run-on analysis indicated that retinoic acid upregulates transcription of the EGF-R gene, reaching a maximum at 48 h and decreasing after 72 h of treatment. When retinoic acid-treated cells were chased in drug-free medium, the increased EGF-R transcript level remained unchanged. Up-regulated expression of EGF-R in H460 cells is reflected by their increasing tumorigenicity phenotype. The results demonstrate that retinoic acid induces EGF-R synthesis in human lung cancer cells. Copyright 1995 S. Karger AG, Basel

Insulin-like growth factor-I is an autocrine regulator for the brain metastatic variant of a human non-small cell lung cell line.

Insulin-like growth factor (IGF-I) is associated with autocrine and paracrine stimulation for cell growth and development of brain tumor cells. The function of IGF-I in the brain metastatic variant of human lung cancer cells is investigated. The cells used here were derived in vivo with intracarotid injection of human non-small cell lung carcinoma NCI-H226. The tumor was developed as a cultured cell line, H226Br. Unlike the parental cells, H226Br was tumorigenic in nu/nu nude mice. Reverse transcriptase-polymerase chain reaction showed that IGF-I transcript of H226Br is increased compared to that of parental cells. The amount of IGF-I secreted in cultured medium of H226Br is higher than that of cultured parental cells. The IGF-I receptor-specific antibody, alpha IR3, inhibits H226Br growth in serum-free culture. The results established that IGF-I is an autocrine growth regulator for human non-small cell lung cancer cells that progressed to brain.

Differential down-regulation of epidermal growth factor receptors expressed in the metastatic variants of human lung cancer adenocarcinoma cell line DMS4C.

The metastatic variants of human lung adenocarcinoma cell line DMS4C were established by selection in vivo. Lung, brain, spleen and liver metastatic tumors derived from intracarotid inoculation of athymic BALB/c mice were collected, and their corresponding variant cell lines established. The epidermal growth factor (EGF) receptor expression of the parental cell line as well as the metastatic variant cell lines were investigated. 125I-labeled EGF binding assays showed that there were two types of EGF receptors in both parental and metastatic variants. Compared to DMS4C, the EGF binding capacities were found to be down-regulated by 70, 79, 85 and 89% for lung, spleen, liver and brain variant, respectively. The dissociation constants of spleen, liver and brain EGF receptors were distinct from that of the parental cell line. The EGF receptor autophosphorylation activity of lung variant was shown to be down-regulated as shown by immune complex kinase assay that corresponded to EGF receptor numbers whereas kinase activities of the liver, spleen and brain variants EGF receptors were completely abolished. However, the 170 kilodalton EGF receptor was shown to be unaltered during metastasis. The results indicated that, during metastasis progression, the proliferation of adenocarcinoma cells may have adopted a different growth regulation that is independent of EGF receptor kinase-modulated autocrine pathway. The result also implies that other oncogene may emerge as the major growth regulator for distant metastasis of adenocarcinoma cancer cells. This work provides a model for understanding tumor metastasis progression of human lung cancer.

In-vivo evaluation of dopamine receptor-mediated inhibition of gonadotrophin secretion from the pituitary gland of the goldfish, Carassius auratus.

Dopamine acts directly on the pituitary to modulate gonadotrophin (GtH) secretion in goldfish (Carassius auratus). In the light of this important role for dopamine in the regulation of goldfish reproduction, this investigation was designed to evaluate the receptor specificity of this dopamine inhibition and to describe the use of domperidone, a specific dopamine D2-receptor antagonist, in the manipulation of pituitary function in goldfish. To investigate the specificity of dopamine inhibition of GtH secretion, selected dopamine receptor antagonists were injected i.p. to block dopamine receptors thereby increasing GtH secretion as reflected by increased serum concentrations of GtH. Serum GtH levels were significantly increased by the active stereoisomer (-)-sulpiride in a dose-related fashion; (+)-sulpiride had no effect. Comparison of dopamine antagonists at low doses indicated that only domperidone and pimozide caused significant increases in serum concentrations of GtH. Dopamine antagonists potentiated the action of a gonadotrophin-releasing hormone analogue (GnRH-A) with an order of potency of domperidone = pimozide greater than metoclopramide = fluphenazine. [3H]Domperidone, injected i.p. with unlabelled domperidone, entered the blood and achieved maximum concentrations 12 h after injection, but did not accumulate in the brain in appreciable amounts. Gonadal 3H radioactivity was usually equal to or in excess of blood radioactivity, while [3H]domperidone was highly concentrated in the pituitary in a time-dependent fashion, with maximal accumulation occurring 24 h after injection. The time-course of pituitary accumulation of [3H]domperidone correlated well with the temporal increase in serum GtH levels in response to i.p. injected domperidone or domperidone plus an analogue of LHRH. Domperidone increased serum concentrations of GtH in a dose-related fashion; an analogue of salmon GnRH (sGnRH-A) increased the sensitivity and magnitude of the serum GtH response to domperidone. Serum concentrations of GtH were increased by sGnRH-A in a dose-related fashion; a low dose of domperidone substantially increased the sensitivity of the serum GtH response to sGnRH-A. These results indicate that dopamine inhibits GtH secretion from the goldfish pituitary by acting through a specific mechanism mediated by a dopamine D2 receptor. Domperidone increased serum concentrations of GtH, potentiated the action of gonadotrophin-releasing hormones and did not pass into the brain after i.p. injection into goldfish. The data also suggest that dopamine and GnRH, although acting through different receptors, influence the effect of each other on GtH release.