Browsing by Issue Date, starting with "2012-09-27"
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- Rac1 signalling modulates a STAT5/BCL-6 transcriptional switch on cell-cycle-associated target gene promotersPublication . Barros, Patricia; Lam, Eric; Jordan, Peter; Matos, PauloGene expression depends on binding of transcriptional regulators to gene promoters, a process controlled by signalling pathways. The transcriptional repressor BCL-6downregulates genes involved in cell cycle progression and becomes inactivated following phosphorylation by the Rac1 GTPase activated protein kinase PAK1.Interestingly, the DNA motifs recognized by BCL-6 and STAT5 are similar. Because STAT5 stimulation in epithelial cells can also be triggered by Rac1 signalling, weasked whether both factors have opposing roles in transcriptional regulation and whether Rac1 signalling may coordinate a transcription factor switch. We usedchromatin immunoprecipitation to show that active Rac1 promotes release of the repressor BCL-6 while increasing binding of STAT5A to a BCL-6-regulated reportergene. We further show in colorectal cell lines that the endogenous activation status of the Rac1/PAK1 pathway correlated with the phosphorylation status of BCL-6and STAT5A. Three cellular genes (cyclin D2, p15INK4B, SUMO1) were identified to be inversely regulated by BCL-6 and STAT5A and responded to Rac1 signalling withincreased expression and corresponding changes in promoter occupancy. Together, our data show that Rac1 signalling controls a group of target genes that arerepressed by BCL-6 and activated by STAT5A, providing novel insights into the modulation of gene transcription by GTPase signalling.
- Protein Kinase WNK2 has a Tumour Suppressor Role in GliomasPublication . Moniz, Sonia; Martinho, Olga; Pinto, Filipe; Reis, Rui Manuel; Jordan, PeterMalignant glioblastoma is the most common and lethal adult brain tumour type. Recently, the promoter region of the protein kinaseWNK2 gene was found to be hypermethylated in 29 of 31 infiltrative gliomas and about 5 of 7 meningiomas. We have previously described that theexperimental depletion of WNK2 expression decreases RhoA activity whilst leading to increased Rac1 activity. RhoA/Rac1 activities are important forcell migration and glioblastomas are very invasive tumours so that we tested the effects of WNK2 on wound-healing assays in glioma cell lines SW1088and A172. SW1088 cells express endogenous WNK2 and we observed that wound closure was increased upon experimental depletion of endogenousWNK2. In contrast, A172 cells display complete promoter region methylation and WNK2 re-expression was found to decrease migration. Consistently,we observed an increase in Rac1 activity in SW1088 cells upon WNK2 down-regulation, but lower levels of active Rac1 in A172 cells stably expressingWNK2 cDNA when compared with an equivalent cell line stably transfected with the same empty vector. Our studies indicate that loss of WNK2expression promotes Rac1 activation and may contribute to the highly invasive phenotype that glioblastomas present.