Date of Award

January 2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical Sciences

First Advisor

Archana Dhasarathy

Abstract

The process of epithelial to mesenchymal transition (EMT), in which epithelial cells assume a mesenchymal cell phenotype with enhanced migratory capacity plays an integral role in development and wound healing but also contributes pathologically to fibrosis and cancer progression. This switch in cell differentiation and behavior is mediated by key transcription factors like SNAI1 (SNAIL) and SNAI2 (SLUG) in response to several signaling pathways like TGF-β and EGF. There are three key events that occur during TGF-β induced EMT, namely extracellular cues that must be transmitted to the nucleus to elicit activation of SNAI1 transcription, recruitment of transcription factors (TFs) to the SNAIL gene and subsequent transcription, and finally propagation of the signaling response over multiple generations to maintain the EMT response.

In study I we show that blocking store-operated calcium entry (SOCE) with 2-aminoethoxydiphenylborane (2APB) reduces cell migration but increases the level of TGF-β mediated Snai1 expression. We also demonstrate that the calcium channel proteins ORAI3 and STIM1 are involved in this increased transcription of Snai1 via the NF-κB -AKT pathway.

In study II we show that the transcription factor CTCF associates with the SNAI1 promoter in steady state cancer cell lines and in TGF-β mediated induction of EMT in non-cancerous cell lines. We observed this association of CTCF with the SNAI1 is stimulus dependent and CTCF might regulate TGF-β mediated Snai1 activation either directly or indirectly.

In study III we established a model to study how cells “remember” previous exposures to environmental stimuli and pass on this memory to future generations, thus enabling them to mount a more robust response when they next encounter the same stimuli. We demonstrated that this “memory” is transmitted across cell divisions and is largely attributed to the acquisition of chromatin marks like H3K4me1, H3K27Ac and loss of repressive mark H3K27me3.

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