All ETDs from UAB

Advisory Committee Chair

Susan L Bellis

Advisory Committee Members

Lalita Shevde-Samant

Christopher Klug

John Parant

Laurie Harrington

Document Type

Dissertation

Date of Award

2023

Abstract

ST6Gal1 sialyltransferase adds negatively charged sialic acid in an α2,6 linkage to N-glycans on glycoproteins bound for the cell surface/secretion thus altering receptor structure, function and downstream signaling pathways. ST6Gal1 is upregulated in multiple cancers, including pancreatic, and imparts cancer stem cell-like phenotype. Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy with a survival rate of ~10%. Acinar to ductal metaplasia (ADM), the tumor initiation stage of PDAC, occurs in response to insults like pancreatitis, when acinar cells dedifferentiate and form ductal-like cells with stem and ductal gene upregulation. These cells, on acquiring mutations such as in KRAS gene, can progress to preneoplastic lesions and PDAC. To investigate ST6Gal1’s role in ADM and PDAC, we designed novel genetically engineered mouse (GEM) models with ST6Gal1 expression alone (SC mice) or with ST6Gal1 plus KrasG12D expression (KSC mice) using Pdx1-Cre, for comparative studies alongside KC mice (KrasG12D alone). KSC mice had dramatically accelerated PDAC progression (median survival 4.3 months), compared to KC mice (median survival 13.6 months). We hypothesized that ST6Gal1 reprograms the acinar cells to become ductal-like, facilitating ADM, and with KrasG12D mutation, accelerates PDAC. Using organoids and cell lines, we demonstrate ST6Gal1-mediated upregulation of ductal gene, Sox9 and downregulation of acinar gene, Ptf1a. SC mice exhibited a significantly higher number of ADM-like cells basally and in cerulein-treated mice as well as Sox9+ acinar cells compared to littermate control mice. Bulk RNA sequencing on GEM pancreata demonstrated gene enrichment for EGFR/ERBB pathways in SC compared to WT. EGFR is activated by ST6Gal1-mediated sialylation and drives Sox9 expression as well as ADM. Immunofluorescence indicated higher p-EGFR in SC and KSC compared to WT and KC respectively. Additionally, SC and KSC organoids confirm higher p-EGFR and Sox9 expression compared to WT and KC organoids. Lastly, xenograft studies demonstrate a causal role for ST6Gal1-high tumor cells in PDAC progression and metastasis. Single cell RNA sequencing on GEM mice demonstrates that ST6Gal1 upregulates genes that aid transition of epithelial cells to neoplastic cells by altering metabolic, proliferative and stemness pathways. Overall, our results highlight a novel role for ST6Gal1 as a tumor driver in PDAC.

Available for download on Friday, December 27, 2024

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