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Regulation of mda-7 gene expression during human melanoma differentiation Madireddi MT; Dent P; Fisher PBOncogene 2000[Mar]; 19 (10): 1362-8Induction of irreversible growth arrest and terminal differentiation in human melanoma cells following treatment with recombinant human fibroblast interferon (IFN-beta) and mezerein (MEZ) results in elevated expression of a specific melanoma differentiation associated gene, mda-7. Experiments were conducted to define the mechanism involved in the regulation of mda-7 expression in differentiating human melanoma cells. The mda-7 gene is actively transcribed in uninduced HO-1 human melanoma cells and the rate of transcription of mda-7 is not significantly enhanced by treatment with IFN-beta, MEZ or IFN-beta+MEZ. The high basal activity of the mda-7 promoter in uninduced melanoma cells and the absence of enhancing effect upon treatment with differentiation inducers is corroborated by transfection studies using the promoter region of mda-7 linked to a luciferase reporter gene containing the SV40 polyadenylation signal sequence. RT - PCR analysis detects the presence of low levels of mda-7 transcripts in uninduced and concomitant increases in differentiation inducer treated HO-1 cells. However, steady-state mda-7 mRNA is detected only in IFN-beta+MEZ and to a lesser degree in MEZ treated cells. We show that induction of terminal differentiation of HO-1 cells with IFN-beta+MEZ dramatically increases the half-life of mda-7 mRNA while treatment with cycloheximide results in detectable mda-7 mRNA in control and inducer treated cells. These observations confirm constitutive activity of the mda-7 promoter in HO-1 cells irrespective of differentiation status suggesting posttranscriptional processes as important determinants of mda-7 expression during terminal differentiation. The 3' UTR region of mda-7 contains AU-rich elements (ARE) that contribute to rapid mda-7 mRNA turnover during proliferation and reversible differentiation, a process controlled by a labile protein factor(s). Substitution of the SV40 polyadenylation signal sequence in the luciferase reporter plasmid with the mda-7-ARE-3'-UTR renders the Luciferase message unstable when expressed in proliferating and reversibly differentiated melanoma cells. In contrast, the luciferase message is stabilized when the mda-7-ARE-3'-UTR construct is expressed in terminally differentiated HO-1 cells. These results provide compelling evidence that mda-7 expression during terminal differentiation in human melanoma cells is regulated predominantly at a posttranscriptional level.|*Diterpenes[MESH]|*Gene Expression Regulation, Neoplastic[MESH]|*Interleukins[MESH]|*RNA Processing, Post-Transcriptional[MESH]|3' Untranslated Regions[MESH]|Base Sequence[MESH]|Cell Differentiation[MESH]|Cloning, Molecular[MESH]|Cycloheximide/pharmacology[MESH]|Dactinomycin/pharmacology[MESH]|Genes, Tumor Suppressor[MESH]|Growth Substances/biosynthesis/*genetics[MESH]|Humans[MESH]|Interferon-beta/pharmacology[MESH]|Melanoma/*genetics/pathology[MESH]|Molecular Sequence Data[MESH]|Promoter Regions, Genetic[MESH]|RNA Stability/drug effects[MESH]|RNA, Messenger/metabolism[MESH]|Terpenes/pharmacology[MESH] |
