Mxi1 inhibits the proliferation of U87 glioma cells through down-regulation of cyclin B1 gene expression.
Mxi1 is a Mad family member that plays a role in cell proliferation and differentiation. To test the role of Mxi1 on tumorigenesis of glioma cells we transfected a CMV-driven MXI1 cDNA in U87 human glioblastoma cells. Two clones were isolated expressing MXI1 levels 18- and 3.5-fold higher than wild-type U87 cells (clone U87.Mxi1.14 and U87.Mxi1.22, respectively). In vivo, U87.Mxi1.14 cells were not tumorigenic in nude mice and delayed development of tumours was observed with U87.Mxi1.22 cells. In vitro, the proliferation rate was partially and strongly inhibited in U87.Mxi1.22 and U87.Mxi1.14 cells respectively. The cell cycle analysis revealed a relevant accumulation of U87.Mxi1.14 cells in the G(2)/M phase. Interestingly, the expression of cyclin B1 was inhibited to about 60% in U87.Mxi1.14 cells. This inhibition occurs at the transcriptional level and depends, at least in part, on the E-box present on the cyclin B1 promoter. Consistent with this, the endogenous Mxi1 binds this E-box in vitro. Thus, our findings indicate that Mxi1 can act as a tumour suppressor in human glioblastomas through a molecular mechanism involving the transcriptional down-regulation of cyclin B1 gene expression.
Manni
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I
Istituto Regina Elena, Centro Ricerca Sperimentale, Laboratorio di Oncogenesi Molecolare, Via delle messi D'Oro 156, 00158 Rome, Italy.
Tunici
P
P
Cirenei
N
N
Albarosa
R
R
Colombo
B M
BM
Roz
L
L
Sacchi
A
A
Piaggio
G
G
Finocchiaro
G
G
D051792:Basic Helix-Loop-Helix Proteins; D002453:Cell Cycle / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology*; D002455:Cell Division / Q000187:drug effects* / Q000502:physiology*; D019926:Cyclin B / Q000235:genetics*; D056744:Cyclin B1; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D016195:G2 Phase; D015972:Gene Expression Regulation, Neoplastic; D017930:Genes, Reporter; D005910:Glioma; D006801:Humans; D007700:Kinetics; D008938:Mitosis; D011994:Recombinant Proteins / Q000494:pharmacology; D013997:Time Factors; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
D051792:Basic Helix-Loop-Helix Proteins; D019926:Cyclin B; D056744:Cyclin B1; D004268:DNA-Binding Proteins; D011994:Recombinant Proteins; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; C534699:CCNB1 protein, human; C534700:Ccnb1 protein, mouse; C079440:MXI1 protein, human