mezerein and Osteosarcoma

Abnormalities in cellular differentiation are frequent occurrences in human cancers. Treatment of human melanoma cells with recombinant fibroblast interferon (IFN-beta) and the protein kinase C activator mezerein (MEZ) results in an irreversible loss in growth potential, suppression of tumorigenic properties and induction of terminal cell differentiation. Subtraction hybridization identified melanoma differentiation associated gene-7 (mda-7), as a gene induced during these physiological changes in human melanoma cells. Ectopic expression of mda-7 by means of a replication defective adenovirus results in growth suppression and induction of apoptosis in a broad spectrum of additional cancers, including melanoma, glioblastoma multiforme, osteosarcoma and carcinomas of the breast, cervix, colon, lung, nasopharynx and prostate. In contrast, no apparent harmful effects occur when mda-7 is expressed in normal epithelial or fibroblast cells. Human clones of mda-7 were isolated and its organization resolved in terms of intron/exon structure and chromosomal localization. Hu-mda-7 encompasses seven exons and six introns and encodes a protein with a predicted size of 23.8 kDa, consisting of 206 amino acids. Hu-mda-7 mRNA is stably expressed in the thymus, spleen and peripheral blood leukocytes. De novo mda-7 mRNA expression is also detected in human melanocytes and expression is inducible in cells of melanocyte/melanoma lineage and in certain normal and cancer cell types following treatment with a combination of IFN-beta plus MEZ. Mda-7 expression is also induced during megakaryocyte differentiation induced in human hematopoietic cells by treatment with TPA (12-O-tetradecanoyl phorbol-13-acetate). In contrast, de novo expression of mda-7 is not detected nor is it inducible by IFN-beta+MEZ in a spectrum of additional normal and cancer cells. No correlation was observed between induction of mda-7 mRNA expression and growth suppression following treatment with IFN-beta+MEZ and induction of endogenous mda-7 mRNA by combination treatment did not result in significant intracellular MDA-7 protein. Radiation hybrid mapping assigned the mda-7 gene to human chromosome 1q, at 1q 32.2 to 1q41, an area containing a cluster of genes associated with the IL-10 family of cytokines. Mda-7 represents a differentiation, growth and apoptosis associated gene with potential utility for the gene-based therapy of diverse human cancers.

Topics: Antigens, Neoplasm; Apoptosis; Base Sequence; Carcinoma; Cell Differentiation; Cell Division; Chromosomes, Human, Pair 1; Cloning, Molecular; Dimethyl Sulfoxide; Diterpenes; Female; Gene Expression Regulation, Neoplastic; Genes; Genes, Tumor Suppressor; Glioblastoma; Growth Substances; HL-60 Cells; Humans; Interferon Type I; Interleukins; K562 Cells; Male; Melanocytes; Melanoma; Molecular Sequence Data; Molecular Weight; Neoplasm Proteins; Neoplasms; Organ Specificity; Osteosarcoma; Recombinant Fusion Proteins; Recombinant Proteins; RNA, Messenger; RNA, Neoplasm; Terpenes; Tetradecanoylphorbol Acetate; Transfection; Tumor Cells, Cultured

The phorbol ester analog, mezerein, is a weak complete and Stage 1 tumor promoter; however, it is as potent as the most active phorbol esters as a second stage promoter and inflammatory agent. Therefore, mezerein is a useful compound for studying responses associated with Stage 1 or Stage 2 promotion. In this paper, we show that in G-292 osteosarcoma cells in culture, mezerein is 25-fold more potent in causing a decrease in binding of epidermal growth factor to its specific cellular receptor than in inducing prostaglandin E2 production. This differential potency for these two actions was not noted for other phorbol esters. Our findings indicate that mezerein interacts with the major phorbol dibutyrate receptor to increase prostaglandin E2 production and also either with a distinct cellular target with a higher affinity or the same target with increased efficacy to cause a decrease in the binding of epidermal growth factor. These human osteosarcoma cells thus provide a model system to facilitate analysis of phorbol ester receptor heterogeneity.

Topics: Binding, Competitive; Caenorhabditis elegans Proteins; Carrier Proteins; Dinoprostone; Diterpenes; Epidermal Growth Factor; Humans; Kinetics; Osteosarcoma; Phorbol 12,13-Dibutyrate; Phorbol Esters; Phorbols; Prostaglandins E; Protein Kinase C; Receptors, Drug; Terpenes; Tetradecanoylphorbol Acetate