Differential induction of cell death in human glioma cell lines by sodium nitroprusside.

BACKGROUND: High grade gliomas represent very aggressive and lethal forms of human cancer, which often exhibit recurrence after surgical intervention and resistance to conventional chemotherapeutic and radiologic treatment. The clinically approved antihypertensive agent sodium nitroprusside (SNP) has been shown to induce cytotoxicity toward a number of carcinoma cell lines in vitro. METHODS: Three human glioma cell lines were examined for susceptibility to the cytotoxic effects of SNP. The role of the protein kinase C (PKC)alpha gene in mediating resistance to SNP-induced killing in U343 cells was investigated using antisense oligonucleotide inhibition. Stable transfection and overexpression of the PKCalpha gene in the SNP-susceptible cell line U251 was performed to further implicate PKCalpha as a mediating factor in SNP cytotoxicity. In addition, the presence of bcl-2 protein in these cells was examined for possible correlation(s) with resistance to SNP. RESULTS: Exposure of U251 cells and LN-Z308 cells to 0.5 mM SNP resulted in significant cytotoxicity over a 72-hour period. U343 cells were resistant to SNP killing. U343 cells were shown to exhibit higher basal levels of PKCalpha and bcl-2 than either U251 or LN-Z308 cells. bcl-2 expression and resistance to SNP toxicity both were decreased by the introduction of PKCalpha antisense oligonucleotides into U343 cells. Conversely, enhanced PKC activity in PKCalpha-transfected U251 clones was associated with increased bcl-2 expression and greater resistance to SNP-induced toxicity relative to control transfected cells. CONCLUSIONS: SNP can induce cytotoxicity in glioma cells. The susceptibility of these glioma cells to nitroprusside-induced killing appears to be correlated inversely with bcl-2 and PKC activity. bcl-2 levels in these cells can be altered through modulation of PKC signaling, specifically, by induction or inhibition of PKCalpha. These in vitro results provide an interesting basis for further study into the potential use of SNP for treatment of human gliomas in patients receiving combination therapy with conventional chemotherapeutic agents that exhibit PKC inhibitory activity.

Monoclonal antibodies to alpha 2u-globulin and immunocytofluorometric analysis of alpha 2u-globulin-synthesizing hepatocytes during androgenic induction and aging.

Stable hybridomas generated by fusion of spleen cells from hyperimmunized mice and mouse myeloma cells were cloned to prepare monoclonal antibodies to alpha 2u-globulin, an androgen-dependent urinary protein of hepatic origin. One of these monoclonal antibodies was used as a probe for immunocytofluorometric analysis of alpha 2u-globulin producing hepatocytes during androgenic induction and aging through fluorescence-activated cell sorting (FACS). FACS patterns of hepatocytes from mature male rats that produce high levels of alpha 2u-globulin showed tow distinct peaks, arbitrarily designated as peak I (weakly fluorescent) and peak II (brightly fluorescent). In the mature male rat, peak II represented about 40% of the total hepatocytes, and the fluorescence intensity of this subpopulation decreased in direct correspondence with the gradual decline of alpha 2u-globulin synthesis during aging. Similarly the androgenic induction of this protein in ovariectomized female rats was associated with an increase in the fluorescence intensity of the hepatocyte subpopulation under peak II rather than an increase in the relative number of these cells. From these results we conclude that the androgen-dependent synthesis of alpha 2u-globulin and its alteration during aging are confined to a specific subpopulation of hepatocytes within the liver.

Age-dependent regulation of the polymorphic forms of alpha 2u-globulin.

Hepatic synthesis of alpha 2u-globulin in the male rat shows a gradual decline and ultimate loss during aging and senescence. Northern blot analysis with a cloned cDNA probe showed that the decrease in alpha 2u-globulin synthesis during aging is associated with a corresponding decrease in the concentration of its hepatic mRNA. By means of two-dimensional gel electrophoresis, alpha 2u-globulin is resolved into a family of proteins. A monoclonal mouse antibody can identify at least five major isoelectric variants of alpha 2u-globulin within the total protein synthesized by rat hepatocytes. These isoelectric variants are also present in the in vitro translation products of hepatic mRNA. An examination of the hepatic synthesis of the isoelectric variants of alpha 2u-globulin during aging showed a differential regulation of the variant forms of this protein. Variant 2 (pI 6.1, the most prominent form) is the first to appear at puberty (40 days). The weakest member of the five major isoelectric forms (variant 4, pI 4.1) is the last to disappear at senescence. Although the overall decline in alpha 2u-globulin synthesis during aging seems to be due to an age-dependent decrease in the androgen responsiveness of hepatocytes, it is postulated that the differential regulation of the isoelectric variants may represent changes at the level of the genes coding for this protein.

Pretranslational regulation of alpha 2u-globulin in rat liver by growth hormone.

Hypophysectomy is known to cause complete suppression of the hepatic synthesis alpha 2u-globulin. The effect of hypophysectomy on the synthesis of alpha 2u-globulin can be reversed by multiple hormone treatment. The role of pituitary growth hormone in the multihormonal regulation of alpha 2u-globulin in rat liver was examined in the hypophysectomized male rats with and without growth hormone supplementation. Daily treatment of hypophysectomized rats with 5 alpha-dihydrotestosterone, corticosterone, thyroxine, and growth hormone for 8 days caused about 80% recovery in the hepatic content of alpha 2u-globulin and its corresponding mRNA as determined by radioimmunoassay, in vitro translation, and liquid hybridization with a cloned cDNA probe. However, omission of growth hormone from the treatment regimen failed to raise hepatic alpha 2u-globulin and its mRNA to more than 5% of the normal control. The possible effect of growth hormone on the translation of the mRNA for alpha 2u-globulin was examined with cultured hepatocytes derived from growth hormone-deficient rats. Culture of these cells in the presence of growth hormone for 24 h did not turn on the synthesis of alpha 2u-globulin. These results indicate that growth hormone regulates the synthesis of alpha 2u-globulin by acting at a step antecedent to mRNA translation.

Synthesis and processing of the dimorphic forms of rat alpha 2u-globulin.

alpha 2u-Globulin the androgen-dependent male rat urinary protein, can be resolved into two distinct molecular forms by SDS-polyacrylamide slab gel electrophoresis. These two forms designated as alpha 2u-A (M, 18,800) and alpha 2u (Mr 18,100) are found both in urine and in the liver cells. Translation of rat liver mRNA in the rabbit reticulocyte lysate produced two preprotein forms of alpha 2u-globulin, designated as alpha 2uA' (Mr 20,300) and alpha 2uB' (Mr 19,600). Cell-free translation of rat liver mRNA in the presence of dog pancreas microsomal membrane or in Xenopus oocytes produced the two processed forms of alpha 2u-globulin (alpha 2uA and alpha 2uB). Quantitation of alpha 2uA and alpha 2uB within the in vitro translation products of the hepatic mRNA from albino rats of Yale, Sprague-Dawley and Fischer strains showed genetic differences in the proportion of translatable mRNA for alpha 2uA and alpha 2uB. The ratio of alpha 2uA: alpha 2uB in the translation products of liver mRNA from Yale rats was found to be 1:2.5 while in the case of both Sprague-Dawley and Fischer rats, the ratio was 1:4. A small portion of the alpha 2uA and alpha 2uB synthesized in the cultured hepatocytes, in the Xenopus oocytes or in the membrane-supplemented cell-free system appeared as two additional forms, designated as alpha 2uA" (Mr 21,200) and alpha 2uB" (Mr 20,600). Unlike alpha 2uA and alpha 2uB both alpha 2uA" and alpha 2uB" were found to bind to Con A-Sepharose, suggesting their glycoprotein nature.

Multiple hormone requirement for the synthesis of alpha 2u-globulin by monolayers of rat hepatocytes in long term primary culture.

Primary cultures of adult rat hepatocytes were prepared by releasing liver cells through fractional trypsinization and by a novel nonenzymatic procedure involving the imprinting of liver explants on the surface of the culture flask (explant imprinting). The comparative properties of these two primary cultures and their abilities to synthesize alpha 2u-globulin under multihormonal stimulation were investigated. The hepatocytes isolated from male rats by fractional trypsinization were found to divide rapidly and form a confluent monolayer within 5-7 days of culture. However, these cells failed to synthesize alpha 2u-globulin even after treatment with 5 alpha-dihydrotestosterone, GH, T3, and dexamethasone, hormones with known stimulatory effects on the synthesis of alpha 2u-globulin in vivo. On the contrary, hepatocytes prepared from male rats by the nonenzymatic procedure of explant imprinting were found to synthesize alpha 2u-globulin for more than 2 weeks and responded to GH, T3, and dexamethasone with enhanced production of this protein. Fortification of the culture medium with all of the above three hormones caused an approximately 9-fold enhancement of alpha 2u production within 4 days of culture compared to production in control culture without these hormones. The above results substantiate earlier findings concerning the multiple hormonal requirement for hepatic synthesis of alpha 2u-globulin in vivo and show that isolation and culture of hepatocytes by nonenzymatic explant imprinting may serve as a useful procedure for studying endocrine regulation of gene activity in vitro.