Oncogenic human papillomaviruses block expression of the B-cell translocation gene-2 tumor suppressor gene

Human papillomavirus (HPV)-induced carcinogenesis is critically dependent on the activities of the viral E6 and E7 oncogenes. Here, we demonstrate that expression of the putative tumor suppressor gene B-cell translocation gene-2 (BTG2) is reinduced in HPV16- and HPV18-positive cancer cells on silencing of viral oncogene expression, indicating that BTG2 is repressed by oncogenic HPVs. Inhibition of BTG2 expression was mediated by the HPV E6 oncogene and occurred in a p53-dependent manner. Luciferase reporter gene analyses revealed that BTG2 repression takes place at the transcriptional level and is dependent on the integrity of the major p53-response element within the BTG2 promoter. Ectopic expression of BTG2 acted antiproliferative in cervical cancer cells. Tissue specimens commonly exhibited reduced BTG2 protein levels in HPV-positive high-grade lesions (CIN2/3) and cervical carcinomas, when compared with normal cervical epithelium. These findings identify the antiproliferative BTG2 gene as a novel cellular target blocked by the HPV E6 oncoprotein

The oncogenic fusion protein RUNX1-CBFA2T1 supports proliferation and inhibits senescence in t(8;21)-positive leukaemic cells-0

<p><b>Copyright information:</b></p><p>Taken from "The oncogenic fusion protein RUNX1-CBFA2T1 supports proliferation and inhibits senescence in t(8;21)-positive leukaemic cells"</p><p>BMC Cancer 2004;4():44-44.</p><p>Published online 6 Aug 2004</p><p>PMCID:PMC512292.</p><p>Copyright © 2004 Martinez et al; licensee BioMed Central Ltd.</p> electroporation with 100 nM siRNAs and analyzed by immunoblotting. The electroporated cells and siRNAs are indicated on top. Arrows on the right mark RUNX1-CBFA2T1 and RUNX1 proteins. Markers are shown on the left, and the relative ratios between RUNX1-CBFA2T1 and RUNX1 are indicated below the blot. B. Time course of siRNA-mediated RUNX1-CBFA2T1 depletion. Kasumi-1 nuclear lysates were isolated at the indicated days after electroporation with 100 nM siRNA and analyzed by immunoblotting. Values were normalized to the control siRNA siAGF6

The oncogenic fusion protein RUNX1-CBFA2T1 supports proliferation and inhibits senescence in t(8;21)-positive leukaemic cells-6

<p><b>Copyright information:</b></p><p>Taken from "The oncogenic fusion protein RUNX1-CBFA2T1 supports proliferation and inhibits senescence in t(8;21)-positive leukaemic cells"</p><p>BMC Cancer 2004;4():44-44.</p><p>Published online 6 Aug 2004</p><p>PMCID:PMC512292.</p><p>Copyright © 2004 Martinez et al; licensee BioMed Central Ltd.</p>A was isolated on day 8 and analyzed by real-time RT-PCR. The columns and error bars represent the means and standard deviations of three independent experiments. B. Cell cycle distribution of siRNA-treated cells in the absence and presence of growth factors. Kasumi-1 cells were analyzed on day 8 by FACS analysis as described in Materials and Methods. C. Amount of S phase cells in dependence on the length of RUNX1-CBFA2T1 depletion. D. Amount of senescent cells dependence on the length of RUNX1-CBFA2T1 depletion. Growth factors are indicated below the graphs. The data shown in B, C and D were obtained from the same time course experiment. Cells were electroporated with the indicated siRNAs at days 0, 4, 8 and 12, and were analyzed on days 4, 8, 12 and 16

The oncogenic fusion protein RUNX1-CBFA2T1 supports proliferation and inhibits senescence in t(8;21)-positive leukaemic cells-3

<p><b>Copyright information:</b></p><p>Taken from "The oncogenic fusion protein RUNX1-CBFA2T1 supports proliferation and inhibits senescence in t(8;21)-positive leukaemic cells"</p><p>BMC Cancer 2004;4():44-44.</p><p>Published online 6 Aug 2004</p><p>PMCID:PMC512292.</p><p>Copyright © 2004 Martinez et al; licensee BioMed Central Ltd.</p>rmined at the indicated days using trypan blue counting. Arrows indicate electroporations. B. Graphical representation of cell doubling times. The columns represent the means of three independent experiments. Error bars indicate standard deviations. *, p < 0.05 according to Student's t-test. C. Graphical representation of the cell cycle phase distribution. Kasumi-1 cells were electroporated at days 0 and 4, and were examined at day 8 using FACS analysis. The columns and error bars represent the mean values and standard deviations of three independent experiments. †, p < 0.01 according to Student's t-test. C. RUNX1-CBFA2T1 suppression is associated with increased CDKN1B (p27) levels. After electroporation at days 0 and 4, total cell lysates were prepared at day 8 and analyzed using immunoblotting. After CDKN1B detection, the membrane was stripped and reprobed with an anti-tubulin antibody. The siRNAs are indicated on top. Arrows on the left mark RUNX1-CBFA2T1, RUNX1, CDKN1B (p27) and tubulin proteins. The relative ratios between CDKN1B and tubulin are indicated below the blot

The oncogenic fusion protein RUNX1-CBFA2T1 supports proliferation and inhibits senescence in t(8;21)-positive leukaemic cells

<p>Abstract</p> <p>Background</p> <p>The fusion protein RUNX1-CBFA2T1 associated with t(8;21)-positive acute myeloid leukaemia is a potent inhibitor of haematopoetic differentiation. The role of RUNX1-CBFA2T1 in leukaemic cell proliferation is less clear. We examined the consequences of siRNA-mediated RUNX1-CBFA2T1 depletion regarding proliferation and clonogenicity of t(8;21)-positive cell lines.</p> <p>Methods</p> <p>The t(8;21)-positive cell line Kasumi-1 was electroporated with RUNX1-CBFA2T1 or control siRNAs followed by analysis of proliferation, colony formation, cell cycle distribution, apoptosis and senescence.</p> <p>Results</p> <p>Electroporation of Kasumi-1 cells with RUNX1-CBFA2T1 siRNAs, but not with control siRNAs, resulted in RUNX1-CBFA2T1 suppression which lasted for at least 5 days. A single electroporation with RUNX1-CBFA2T1 siRNA severely diminished the clonogenicity of Kasumi-1 cells. Prolonged RUNX1-CBFA2T1 depletion inhibited proliferation in suspension culture and G1-S transition during the cell cycle, diminished the number of apoptotic cells, but induced cellular senescence. The addition of haematopoetic growth factors could not rescue RUNX1-CBFA2T1-depleted cells from senescence, and could only partially restore their clonogenicity.</p> <p>Conclusions</p> <p>RUNX1-CBFA2T1 supports the proliferation and expansion of t(8;21)-positive leukaemic cells by preventing cellular senescence. These findings suggest a central role of RUNX1-CBFA2T1 in the maintenance of the leukaemia. Therefore, RUNX1-CBFA2T1 is a promising and leukaemia-specific target for molecularly defined therapeutic approaches.</p