Studies on post-transcriptional regulation of ST6Gal1

Ghosh, Manjusha S (2014) Studies on post-transcriptional regulation of ST6Gal1. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS dissertation of Manjusha S Ghosh) MANJUSHA_S_GHOSH_09MS015.pdf - Submitted Version Restricted to Repository staff only Download (2MB)

Abstract

β-galactoside alpha-2, 6-sialyltransferase 1 (ST6Gal-1) belongs to the sialyl-transferase family of enzymes and has two protein isoforms coded by three transcript variants(TVs). It mediates the transfer of sialic acid residues to N-oligosaccharides on proteins and hence contributes to the sialyation patterns on the cell surface. ST6Gal1 is found to be expressed in progenitor stem cells and its up-regulation is reported in breast, colon, and ovarian epithelial cancers. Interestingly its expression has been correlated with increased metastatic potential, therapeutic resistance and cancer stem cell like phenotype of tumors. But, the mechanism of its up-regulation and down-regulation in differentiated cells still remains to be unraveled. By in-silico analysis, the presence of AU rich elements (AREs) and micro-RNA binding sites in the 2750 base pairs long 3‟ UTR of ST6Gal1 mRNA were found, which kindled the hypothesis that the altered expression might be regulated at mRNA stability level. MCF-7, MDA-MB-231 and U937 cancer cell lines were screened for ST6Gal1 expression and only MDA-MB-231 and U937 cells were found to be expressing detectable ST6Gal1 (TV1). Cloning of the ARE containing parts into reporter constructs of pBBB4 (which contains a serum inducible β-globin gene) and pcDNA3-luciferace(which expresses firefly luciferase) were attempted. Phorbol myristate ester (PMA) a PI3 kinase activator has been semi quantitatively found to be down regulating ST6Gal1 expression which could be used as a condition modulating the expression of ST6Gal1 for future experiments. Thus we aim to study the post transcriptional regulation of ST6gal1 gene by identifying the cis acting elements and trans activating proteins and microRNAs to decipher some of the mysteries of the signaling network involving this gene. Also an interaction of regulatory elements and miRs can be a possible area to be studied in future. Increasing knowledge on the signaling mechanisms will aid developing ST6Gal1 as a biomarker and therapeutic target specifically for cancer stem cells.

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