Regulation of mda-7 gene expression during human melanoma differentiation.
Induction 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.
Madireddi
M T
MT
Department of Urology, Herbert Irving Comprehensive Cancer Center, Columbia University, College of Physicians and Surgeons, New York, NY 10032, USA.
Dent
P
P
Fisher
P B
PB
D020413:3' Untranslated Regions; D001483:Base Sequence; D002454:Cell Differentiation; D003001:Cloning, Molecular; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D004224:Diterpenes; D015972:Gene Expression Regulation, Neoplastic; D016147:Genes, Tumor Suppressor; D006133:Growth Substances / Q000096:biosynthesis / Q000235:genetics*; D006801:Humans; D016899:Interferon-beta / Q000494:pharmacology; D007378:Interleukins; D008545:Melanoma / Q000235:genetics* / Q000473:pathology; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012323:RNA Processing, Post-Transcriptional; D020871:RNA Stability / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D013729:Terpenes / Q000494:pharmacology; D000099180:Interleukin-24
D020413:3' Untranslated Regions; D003513:Cycloheximide; D003609:Dactinomycin; D004224:Diterpenes; D006133:Growth Substances; D016899:Interferon-beta; D007378:Interleukins; D012333:RNA, Messenger; D013729:Terpenes; D000099180:Interleukin-24; C011309:mezerein