RESUMEN
The special AT-rich DNA-binding protein 1 (SATB1) is a matrix attachment region (MAR)-binding protein that acts as a global repressor via recruitment of CtBP1:HDAC1-containing co-repressors to its binding targets. The N-terminal PSD95/Dlg-A/ZO-1 (PDZ)-like domain of SATB1 mediates interactions with several chromatin proteins. In the present study, we set out to address whether the PDZ-domain-mediated interactions of SATB1 are critical for its in vivo function as a global repressor. We reasoned that since the N-terminal PDZ-like domain (amino acid residues 1–204) lacks DNA binding activity, it would fail to recruit the interacting partners of SATB1 to its genomic binding sites and hence would not repress the SATB1-regulated genes. Indeed, in vivo MAR-linked luciferase reporter assay revealed that overexpression of the PDZ-like domain resulted in de-repression, indicating that the PDZ-like domain exerts a dominant negative effect on genes regulated by SATB1. Next, we developed a stable dominant negative model in human embryonic kidney (HEK) 293T cells that conditionally expressed the N-terminal 1–204 region harbouring the PDZ-like domain of SATB1. To monitor the effect of sequestration of the interaction partners on the global gene regulation by SATB1, transcripts from the induced and uninduced clones were subjected to gene expression profiling. Clustering of expression data revealed that 600 out of 19000 genes analysed were significantly upregulated upon overexpression of the PDZ-like domain. Induced genes were found to be involved in important signalling cascades and cellular functions. These studies clearly demonstrated the role of PDZ domain of SATB1 in global gene regulation presumably through its interaction with other cellular proteins.
RESUMEN
Cervical cancer is a leading cause of cancer-related deaths among women in India.Human papillomavirus (HPV) infection is the causative agent of cervical cancer; and infection with the high-risk genotypes, predominantly HPV16 and 18,is the biggest risk factor.Vaccines targeting HPV16 and 18 have been found to confer protection in large- scale clinical trials.HPV genotyping has traditionally been carried out to screen the population "at risk" using indirect methods based on polymerase chain reaction (PCR) using consensus primers combined with various DNA hybridization techniques,and often followed by the sequencing of candidate products.Recently,a high-throughput and direct method based on DNA sequencing has been described for HPV genotyping using multiplex pyrosequencing. We present a pilot study on HPV genotyping of cervical cancer and non-malignant cervical samples using multiplex pyrosequencing.Using genomic DNA from cell lines,cervical biopsies,surgical tissues or formalin-fixed,paraffin- embedded tissue samples,we could successfully resolve 6 different HPV types out of the 7 tested,with their prevalence found to be in agreement with earlier reports. We also resolved coinfections with two different HPV types in several samples. An HPV16 genotype with a specific and recurrent sequence variation was observed in 8 cancer samples and one non-malignant sample. We find this technique eminently suited for high-throughput applications,which can be easily extended to large sample cohorts to determine a robust benchmark for HPV genotypes prevalent in India.