Biomedical subjects

Michaël Jeanblanc

Publications and source records attributed to Michaël Jeanblanc.

4 recordsLinked to original sources

PubMed2005

The retinoblastoma gene and its product are targeted by ICBP90: a key mechanism in the G1/S transition during the cell cycle.

The retinoblastoma protein (pRB) is encoded by the RB1 gene whose promoter contains several putative binding sites for ICBP90 (Inverted CCAAT box Binding Protein of 90 kDa), a transcriptional regulator of the topoisomerase IIalpha gene. ICBP90 has two consensus binding sites for pRB in its primary sequence. Here, we show that pRB and ICBP90 co-immunoprecipitate in cell extracts of proliferating human lung fibroblasts and of proliferating or confluent Jurkat cells. GST pull-down assays and immunocytochemistry, after cell synchronization in late G1 phase, confirmed this interaction. Overexpression of ICBP90 induces downregulation of pRB expression in lung fibroblasts as a result of mRNA decrease. DNA chromatin immunoprecipitation experiment shows that ICBP90 binds to the RB1 gene promoter under its methylated status. Overexpression of ICBP90 increases the S and G2/M phase cell fractions of serum-starved lung fibroblasts as assessed by flow cytometry analysis and increases topoisomerase IIalpha expression. Together, these results show that ICBP90 regulates pRB at the protein and gene transcription levels, thus favoring the entry into the S phase of the cells. We propose that ICBP90 overexpression, found in cancer cells, is involved in the altered checkpoint controls occurring in cancerogenesis.

Blotting, Western↗

PubMed2005

TCR pathway involves ICBP90 gene down-regulation via E2F binding sites.

Antigen-induced cell death is essential for function, growth and differentiation of T-lymphocytes through legation of the T cell receptor. Since TCR-induced cell death occurs at late G1 checkpoint of the cell cycle and considering that ICBP90 is critical for G1/S transition, we studied the ICBP90 regulation through the TCR pathway in Jurkat cells. ICBP90 expression was strongly decreased after TCR triggering concomitantly to cyclin D3 and topoisomerase IIalpha expression decreases. Cell stimulation with PMA and/or calcium ionophore A23187 down-regulated ICBP90 expression. The decrease of ICBP90 protein and mRNA expressions was accompanied with cell growth arrest. A luciferase reporter assay demonstrated that activation of TCR pathways inhibit ICBP90 gene promoter activity. Three consensus E2F binding sites (called from E2F-a to E2F-c) were identified in the ICBP90 gene promoter and were subjected to mutations. The E2F-a, located in a highly active promoter fragment, shows a strong positive functional activity in proliferating cells. E2F-a and E2F-c binding sites are involved in the TCR-induced down-regulation of ICBP90 gene transcription. Altogether, our data demonstrate that TCR signaling pathways regulate ICBP90 gene expression through pRb/E2F complex. We propose that ICBP90 down-regulation is a key event in G1 arrest preceding T cell death.

Base Sequence↗

PubMed2005

1,25-Dihydroxyvitamin D3 induces splenocyte apoptosis and enhances BALB/c mice sensitivity to toxoplasmosis.

The hormonal form of Vitamin D, 1,25-dihydroxyvitamin D3, is well known for its immunosuppressive, anti-proliferative and pro-apoptotic activities. In the present work, we studied the effect of 1,25-dihydroxyvitamin D3 on Toxoplasma gondii-infected mice. We observed that 1,25-dihydroxyvitamin D3 reduces the survival rate of infected mice by up to 37% at day 10 post-infection compared to untreated infected mice (P < 0.0001). IFN-gamma and IL-12p40 levels were significantly reduced by 1,25-dihydroxyvitamin D3 in infected mice sera indicating an inhibition of Th-1-type cytokines. CD4+ T lymphocyte and splenocyte counts were also reduced following 1,25-dihydroxyvitamin D3 treatment and a marked induction of apoptosis, accompanied with down-regulation of the anti-apoptotic proteins Bcl-2 and Bcl-X(L), was observed. The above results indicate that 1,25-dihydroxyvitamin D3 induces splenocyte apoptosis and enhances host susceptibility to toxoplasmosis.

Animals↗

PubMed2004

Phosphorylation of ICBP90 by protein kinase A enhances topoisomerase IIalpha expression.

Inverted CCAAT box binding protein of 90kDa (ICBP90) is a nuclear protein involved in the topoisomerase IIalpha (TopoIIalpha) gene expression. It belongs to a family of E3 ligases of the RING finger type and its expression is deregulated in cancer cells. Previous studies have shown that high expression of ICBP90 may impair the control of G1/S transition of the cell cycle in various cancer cell lines. Since PKA signaling pathway is involved in G1/S transition of the cell cycle, the aim of the present study was to investigate whether cAMP signaling pathways involve phosphorylation of ICBP90. Here, we show that phosphorylation of ICBP90 through the cAMP signaling pathway accelerates exit of forskolin-treated cells from the G1 phase and increases binding of ICBP90 to the ICB2 element of the TopoIIalpha gene promoter with a subsequent increase of TopoIIalpha expression. We identify S298 of ICBP90 as target for PKA. We propose that cAMP signaling pathway enhances TopoIIalpha expression through ICBP90 phosphorylation, which may be one of the major events involved in the G1/S transition.

Amino Acid Sequence↗