Restoration of p53 function in anaplastic Wilms' tumor

Characterization of FKGK18 as inhibitor of group VIA Ca2+-independent phospholipase A2 (iPLA2β): candidate drug for preventing beta-cell apoptosis and diabetes

Ongoing studies suggest an important role for iPLA2β in a multitude of biological processes and it has been implicated in neurodegenerative, skeletal and vascular smooth muscle disorders, bone formation, and cardiac arrhythmias. Thus, identifying an iPLA2βinhibitor that can be reliably and safely used in vivo is warranted. Currently, the mechanism-based inhibitor bromoenol lactone (BEL) is the most widely used to discern the role of iPLA2β in biological processes. While BEL is recognized as a more potent inhibitor of iPLA2 than of cPLA2 or sPLA2, leading to its designation as a "specific" inhibitor of iPLA2, it has been shown to also inhibit non-PLA2 enzymes. A potential complication of its use is that while the S and R enantiomers of BEL exhibit preference for cytosol-associated iPLA2β and membrane-associated iPLA2γ, respectively, the selectivity is only 10-fold for both. In addition, BEL is unstable in solution, promotes irreversible inhibition, and may be cytotoxic, making BEL not amenable for in vivo use. Recently, a fluoroketone (FK)-based compound (FKGK18) was described as a potent inhibitor of iPLA2β. Here we characterized its inhibitory profile in beta-cells and find that FKGK18: (a) inhibits iPLA2β with a greater potency (100-fold) than iPLA2γ, (b) inhibition of iPLA2β is reversible, (c) is an ineffective inhibitor of α-chymotrypsin, and (d) inhibits previously described outcomes of iPLA2β activation including (i) glucose-stimulated insulin secretion, (ii) arachidonic acid hydrolysis; as reflected by PGE2 release from human islets, (iii) ER stress-induced neutral sphingomyelinase 2 expression, and (iv) ER stress-induced beta-cell apoptosis. These findings suggest that FKGK18 is similar to BEL in its ability to inhibit iPLA2β. Because, in contrast to BEL, it is reversible and not a non-specific inhibitor of proteases, it is suggested that FKGK18 is more ideal for ex vivo and in vivo assessments of iPLA2β role in biological functions.

Expression pattern, regulation, and functions of methionine adenosyltransferase 2beta splicing variants in hepatoma cells

BACKGROUND & AIMS

Methionine adenosyltransferase (MAT) catalyzes S-adenosylmethionine biosynthesis. Two genes (MAT1A and MAT2A) encode for the catalytic subunit of MAT, while a third gene (MAT2beta) encodes for a regulatory subunit that modulates the activity of MAT2A-encoded isoenzyme. We uncovered multiple splicing variants while characterizing its 5'-flanking region. The aims of our current study are to examine the expression pattern, regulation, and functions of the 2 major variants: V1 and V2.

METHODS

Studies were conducted using RNA from normal human tissues, resected hepatocellular carcinoma specimens, and cell lines. Gene expression, promoter and nuclear binding activities, growth, and apoptosis were measured by routine assays.

RESULTS

MAT2beta is expressed in most but not all tissues, and the 2 variants are differentially expressed. The messenger RNA levels of both variants are markedly increased in hepatocellular carcinoma. Tumor necrosis factor (TNF)-alpha, which induces MAT2A in HepG2 cells, also induced V1 (but not V2) expression. TNF-alpha induced the promoter activity of MAT2beta V1, likely via nuclear factor kappaB and activator protein 1. Both variants regulate growth, but only V1 regulates apoptosis. Reduced expression of V1 led to c-Jun-N-terminal kinase (JNK) activation, apoptosis, and sensitized HepG2 cells to TNF-alpha-induced apoptosis, while overexpression of V1 was protective. However, blocking JNK1 or JNK2 activation did not prevent apoptosis induced by V1 knockdown. V1 (but not V2) knockdown also leads to apoptosis in a colon cancer cell line, suggesting these variants play similar roles in many cell types.

CONCLUSIONS

Different variants of MAT2beta regulate growth and death, which broadens their importance in biology.

Gene therapy: future or flop

Many pediatric diseases have now reached a therapeutic plateau using standard therapy. Gene therapy has emerged as an exciting new means to achieve specific therapeutic benefit. Although there have been important and promising breakthroughs in recent clinical trials, there have been some serious setbacks that have tempered this initial excitement. In this review, we discuss the important developments in the field of gene therapy as it applies to various pediatric diseases and relate the recent successes and failures to the future potential of gene therapy as a medical therapeutic application.

New trends in tumor biology: transfection of a human hepatoblastoma cell line with green fluorescent protein

BACKGROUND/PURPOSE

Enhanced green fluorescent protein (eGFP) is widely used as a marker in different biologic systems. After vector transfection, eGFP is expressed by eukaryotic cells and can be visualized using fluorescent microscopy. The aim of this study was to establish an eGFP-transfected human hepatoblastoma (HB) cell line as tool for further basic research studies.

METHODS

The HB cell line HUH6 was transfected with the pEGFP-N1 vector by liposomal transfection. Enhanced green fluorescent protein-positive cells were sorted out by fluorescence-activated cell sort and selected using G418 resistance. Expression of eGFP-messenger RNA was assessed by single-cell reverse transcriptase polymerase chain reaction after laser microdissection. Original and transfected cells were compared biologically and cytomorphologically.

RESULTS

Vector transfection produced up to 15% eGFP-positive cells. After fluorescence-activated cell sort and G418 selection, a pure cell line was established with 100% eGFP-positive cells. Reverse transcriptase polymerase chain reaction revealed constant expression of eGFP-messenger RNA in fluorescending cells. Analysis of cell characteristics revealed no differences between transfected and original cells.

CONCLUSIONS

For the first time, the authors established an eGFP-transfected HB cell line. This cell line can serve as a promising tool for further studies investigating HB in vitro and in vivo. Our model might also be a basis for similar work on other pediatric solid tumors.

Adenovirus-mediated p53 gene therapy in pediatric soft-tissue sarcoma cell lines: sensitization to cisplatin and doxorubicin

Sarcomas, or tumors of connective tissue, represent roughly 20% of childhood cancers. Although the cure rate for sarcomas in general has significantly improved in the last 10 years, there continue to be subgroups that are difficult to treat. High-grade or metastatic soft-tissue sarcomas and rhabdomyosarcomas (RMS) of the extremities remain therapeutic challenges and their prognosis is often poor. The future of sarcoma therapy will likely include molecular approaches including gene/protein expression profiling and gene-based therapy. Most sarcomas harbor defects in the p53 or pRb pathways. The tumor suppressor p53 is central to regulation of cell growth and tumor suppression and restoring wild-type p53 function in pediatric sarcomas may be of therapeutic benefit. Studies with adenoviral-mediated p53 gene transfer have been conducted in many cancer types including cervical, ovarian, prostatic and head and neck tumors. Studies of this approach, however, remain limited in pediatric cancers, including sarcomas. Using three viral constructs containing cDNA for wild-type p53, mutant p53 (C135S) and lacZ, we studied the effect of adenoviral-mediated gene therapy in four pediatric sarcoma cell lines, RD and Rh4 (RMS), Rh1 (Ewing's sarcoma) and A204 (undifferentiated sarcoma). Using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay, we have shown a dose-dependent decrease in cell viability 72 h post-treatment that occurs with Ad-wtp53 but not with Ad-mutp53. Cells treated with Ad-wtp53 show upregulation of the p53 downstream targets, p21(CIP1/WAF1) and bax. Growth curves demonstrate suppression of cell growth over a period of 4 days and cells treated with Ad-wtp53 demonstrate a significant increase in sensitivity to the chemotherapeutic agents, cisplatin and doxorubicin. Our results indicate that restoration of wild-type p53 function in pediatric sarcoma cells could provide a basis for novel approaches to treatment of this disease.