Synthesis and secretion of transferrin by cultured mouse hepatoma cells

Metastatic growth instructed by neutrophil-derived transferrin

The tumor-promoting functions of neutrophils have been mainly attributed to induction of tumor angiogenesis or suppression of anticancer immunity. However, a direct impact of neutrophils on tumor cell growth and metastasis remains largely uncharacterized. Here, we coupled a proteomic approach with a functional screen to interrogate the secretome of tumor-associated neutrophils. Surprisingly, the iron-transporting protein transferrin was identified as the major mitogen for tumor cells secreted by neutrophils. Depletion of neutrophils inhibited lung metastasis and transferrin production in the metastatic microenvironment. Deletion of transferrin receptor suppressed growth of lung-colonizing tumor cells. Also, media conditioned by neutrophils isolated from metastatic breast cancer patients stimulated growth of human breast cancer cells, an effect that was largely abolished by transferrin immunodepletion. We identified GM-CSF, which is produced primarily by tumor cells, as a selective inducer of de novo transferrin synthesis in neutrophils through the Jak/Stat5β pathway. GM-CSF neutralization or inhibition of Jak kinases curtailed neutrophil transferrin expression in vitro and in vivo as well as cancer metastasis. Thus, transferrin provides a mechanistic link between neutrophils and metastatic growth owing to the ability of tumor-infiltrating neutrophils to locally deliver this growth-promoting protein in response to GM-CSF stimulation. Our study identifies neutrophil-derived transferrin as a key regulator of metastatic tumor cell growth and a therapeutic target for antimetastatic treatment.

Comparative microarray analysis of basal gene expression in mouse Hepa-1c1c7 wild-type and mutant cell lines

Hepa-1c1c7 wild-type and benzo[a]pyrene-resistant derived mutant cell lines have been used to elucidate pathways and mechanisms involving the aryl hydrocarbon receptor (AhR). However, there has been little focus on other biological processes which may differ between the isolated lines. In this study, mouse cDNA microarrays representing 4858 genes were used to examine differences in basal gene expression between mouse Hepa-1c1c7 wild-type and c1 (truncated Cyp1a1 protein), c4 (AhR nuclear translocator, ARNT, deficient), and c12 (low AhR levels) mutant cell lines. Surprisingly, c1 mutants exhibited the greatest number of gene expression changes compared to wild-type cells, followed by c4 and c12 lines, respectively. Differences in basal gene expression were consistent with cell line specific variations in morphology, mitochondrial activity, and proliferation rate. MTT and direct cell count assays indicate both c4 and c12 mutants exhibit increased proliferative activity when compared to wild-type cells, while the c1 mutants exhibited decreased activity. This study further characterizes Hepa-1c1c7 wild-type and mutant cells and identifies significant differences in biological processes that should be considered when conducting comparative mechanistic studies with these lines.

The inhibitory effects of pentamidine on biochemical events in human liver cells

The present study was undertaken to determine the biochemical effects of pentamidine on an established human liver cell line (HEP-G2) and its drug resistant subclone (HEP-G2DR). The HEP-G2DR cells were included in the study in order to determine whether drug resistance played a role in any of the observed effects seen during and/or following pentamidine treatment. The results indicate that a 5 mum concentration of the drug significantly reduced the level of protein synthesis, as well as the continued expression of albumin, a tissue-specific product of both cell lines. Pentamidine also significantly inhibited DNA synthesis in HEP-G2 cells, but not in HEP-G2DR cells, during the first 24 hr. Conversely, only the resistant cells showed a significant recovery in both protein and albumin synthesis after the drug was removed (reversal). The significant recovery in these biochemical parameters was observed during the initial 24-hr reversal period, while a recovery in albumin secretion was not obtained in the HEP-G2 cells even after 72 hr. There was no apparent stimulation in the activity of various phase II drug metabolizing enzymes following pentamidine treatment. These findings suggest that resistance plays a role in the mechanism of action of pentamidine, since biochemical modulation of both cell lines is brought about by the drug, but only the resistant cells appear to recover fully following the removal of pentamidine from the culture medium.

Secretion of albumin and alpha-foetoprotein by dimethylsulphoxide-stimulated hepatocellular carcinoma cells

Exposure of BW77-1 and BW77-2 mouse hepatic tumour cells to the polar solvent dimethylsulphoxide (DMSO) altered extracellular accumulation of albumin and alpha-foetoprotein (AFP) and perturbed their cell cycle kinetics. The amount of albumin secreted into the culture growth medium was dependent on the concentration of DMSO used. Hepatic tumour cells cultured in 1 and 2% DMSO accumulated 50% and 111% more albumin, respectively, than non-DMSO-stimulated cells during the final 24 h of a 4-day exposure to the polar solvent. Commitment of mouse hepatoma cells to increased albumin secretion was temporally dependent, requiring a minimum of 48 h in the presence of DMSO. The AFP level in 1% DMSO-treated cultures was also significantly increased, compared with control cells. Unlike albumin secretion, however, exposure of hepatic tumour cells to 2% DMSO did not further increase (but slightly decreased) extracellular AFP accumulation. Treatment of BW77-1 cells with DMSO resulted in a gradual decline in the percentage of 2C DNA content cells (diploid G1 population) and in a corresponding increase in the proportion of cells with a 4C DNA content (generation of either a G2 or tetraploid G1 population). The extent of this shift directly reflected the concentration of polar solvent in the medium and paralleled the DMSO-induced stimulation in albumin secretion. DMSO-stimulated hepatic tumour cells, therefore, may prove useful in the elucidation of specific regulatory events underlying control of gene expression during the hepatocyte cell cycle.

Generation and chracterization of variants of mouse hepatoma cells with defects in hepato-specific gene expression. I. Albumin synthesis variants

Clonal variants of mouse hepatoma cells that either fail to produce albumin (variant 19/2) or show significantly reduced levels (100-fold less) of albumin production (variant 1/c/1) were isolated from the parental line. Hepa la, after a single exposure to N-methyl-N'-nitrosoguanidine (MNNG). Intracellular levels of albumin in both variants were below detection by our assay. Analyses by cDNA-RNA reassociation kinetics indicate that there are approximately 3900 molecules of cytoplasmic albumin mRNA per cell in the parent and less than 10 molecules per cell in both variants. Southern blotting of the Eco RI restriction fragments of cellular DNA from the parent and variants did not indicate any major deletions in the albumin gene DNA sequences. We conclude that in the two variants studied, processes that regulate albumin production via alterations in the level of cytoplasmic albumin mRNA have been affected. Our analyses have also shown that alpha-fetoprotein (AFP) production is lacking in one variant (19/2) and is slightly reduced in the other (1/c/1). Transferrin secretion is lower than the parental line in both variants. Thus multiple nonlethal defects in hepatic gene expression can be obtained in Hepa la cells in culture that will be useful in determining the number and kinds of genes that control the expression of liver-specific loci.

Molecular mechanism of extinction of liver-specific functions in mouse hepatoma x rat fibroblast hybrids: extinction of the albumin gene

Hybrids formed by the fusion of mouse hepatoma (BWTG3) and rat fibroblast (JF1) cells exhibit the extinction of mouse albumin and alpha-fetoprotein synthesis. Karyotype analyses suggest that all parental chromosomes are present in the hybrids. The extinction, therefore, of mouse hepatocyte genes is attributed to the inhibitory action of the rat genome. In these studies, we show that these hybrids possess and express the mouse beta-glucuronidase gene (which is encoded on the same chromosome as the mouse albumin and alpha-fetoprotein gene), and we present data of Southern blot analysis which demonstrate that such hybrids have indeed retained both mouse and rat albumin DNA sequences. In addition, using mouse albumin cDNA, we have shown by cDNA-RNA reassociation kinetics that albumin mRNA is virtually absent in these hybrids. We conclude from these studies that the extinction of albumin synthesis involves a mechanism which results in the loss of cytoplasmic albumin mRNA.

Immunoprecipitation assay of alpha-fetoprotein synthesis by cultured mouse hepatoma cells treated with estrogens and glucocorticoids

This investigation was to study the biosynthesis of 3H-labeled alpha-fetoprotein (AFP) by cultured mouse hepatoma (HEPA-2) cells. Both the function and regulation of this oncodevelopmental gene are unknown. However, evidence indicates that mechanisms controlling the expression of AFP involve aspects of both normal embryonic development and neoplastic transformation. the secretion of AFP was analyzed during different phases of the growth cycle to provide information on AFP production using standard culture conditions. The highest rate of secretion occurred during the stationary phase, followed by the late logarithmic and early logarithmic phases of growth, respectively. The production of AFP was then determined following the addition of glucocorticoids and estrogens in an attempt to understand hormonal factors that may be involved. Studies utilizing estradiol-17 beta indicated that the secretion of AFP did not appear to be sensitive to this steroid even though sucrose density gradient analysis of HEPA-2 cytosol, for estrogenic receptors, revealed competitive binding moieties on the 8S and 4S regions of the gradient. In contrast, the secretion of the total complement of proteins, including AFP, was significantly stimulated by the glucocorticoids, dexamethasone and corticosterone. Analysis of HEPA-2 cytosol for glucocorticoid receptors revealed binding components in the 7S and 3-4S regions of the gradient. The 3H-dexamethasone binding appeared to be stereospecific since nonlabeled dexamethasone, but not nonlabeled estradiol-17 beta, effectively displaced the bound radioactivity. The glucocorticoid-binding component in HEPA-2 therefore displayed characteristics reported for glucocorticoid receptors in normal liver and other hepatomas.

Isolation of mouse transferrin using salting-out chromatography on Sepharose CL-6B

A new method for the isolation of considerable quantities of mouse transferrin is described. This technique employs salting-out chromatography on Sepharose CL-6B, a new step in the preparation of plasma proteins. This step is followed by ion-exchange chromatography on DEAE-Sepharose CL-6B and gel filtration on Sephacryl S-200. The isolated mouse transferrin was shown to be pure by immunoelectrophoresis, sodium dodecyl sulphate-polyacrylamide gel electrophoresis and by the 465 nm/410 nm ratio of absorbances being 1.41. The molecular weight was determined to be about 77 500. The advantages of this procedure are that it is reproducible, gives a high recovery, and can be extended to a larger scale. The advantage over other protein purification techniques is its general utility, due to the fact that there is no need for species-specific antibodies. The application of this method offers a rapid purification of sufficient quantities of mouse transferrin essential for the elucidation of biological functions of this protein and investigations of its molecular structure.