Graduation Date

Spring 5-6-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Biochemistry & Molecular Biology

First Advisor

Dr. Surinder K Batra

Abstract

Aberrant changes in O-glycosylation patterns underlie pancreatic ductal adenocarcinoma (PDAC) progression and metastasis. Glycosylation is a post-translational modification in which carbohydrate moieties are attached to the protein substrate. My dissertation is focused on mucin-type O-glycosylation, which is the predominant form of O-glycosylation and is regulated by a myriad of glycosyltransferases.

PDAC is one of the most lethal diseases and the mechanistic involvement of aberrant O-glycosylation in its progression and metastasis is unknown. The aberrant glycosylation refers to the appearance of unusual carbohydrate structures such as truncated carbohydrate antigens, often referred to as tumor-associated carbohydrate antigens.

In this dissertation, my goal was to investigate the role of aberrant glycosylation in pancreatic cancer progression. Aberrant glycosylation is attributed to dysfunction in expression/activity of glycosyltransferases. Prior published studies and our preliminary studies indicate loss of expression of O-glycosyltransferases-GALNT3 and C1GALT1 in PDAC. GALNT3 (N-acetylgalactosaminyltransferase 3) is a member of GALNT superfamily of enzymes that initiates mucin-type O-glycosylation. The second step of mucin-type O-glycosylation is catalyzed by C1GALT1 (Core-1 β-3 galactosyltransferase). My thesis is primarily focused on deciphering the mechanistic role of the first enzyme (GALNT3) and a second enzyme (C1GALT1) of mucin-type O-glycosylation in PDAC progression and metastasis.

My results show that GALNT3 is differentially expressed during pancreatic cancer progression. Decreased/loss of expression of GALNT3 was seen in poorly differentiated PDAC as compared to well-differentiated PDAC. This instigated further examination of the functional role of GALNT3 in pancreatic cancer. I performed GALNT3 knockdown studies in four different pancreatic cancer cell lines, and the knockdown cells had altered EGFR and Her2 glycosylation, increased growth, and metastasis.

Apart from GALNT3, which catalyze the first step of O-glycosylation, I have also studied the role of a second enzyme, C1GALT1, in PDAC. C1GALT1 expression studies indicate loss of this glycosyltransferase in a subset of PDAC patients. Further, the expression was dramatically decreased in poorly differentiated PDAC as compared to well-differentiated PDAC. To study the functional implications of the loss of C1GALT1 in PDAC, I performed CRISPR/Cas9-mediated C1GALT1 knockout in two different PDAC cancer cell lines. Knockout of C1GALT1 in PDAC cells lead to aberrant MUC16 glycosylation, increased tumorigenicity and metastasis.

To further elaborate on the functional role of C1galt1, I have developed the KrasG12D; Trp53R172H/+; C1galt1loxP/loxP; Pdx1-Cre (KPCC) mouse model, by crossing C1galt1loxP/loxPmice with KrasG12D; Pdx1-Cre and Trp53R172H/+mice. Knockout of C1galt1 along with Kras and p53 mutations (KPCC mice) significantly decreased overall survival as compared to KPC mice that have Kras and p53 mutations. Early tumors and metastasis were seen for KPCC mice as compared to KPC mice.

In conclusion, I have experimentally shown that the loss of GALNT3 and C1GALT1 in PDAC results in aberrant glycosylation that contributes towards PDAC progression and metastasis.

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