Doctor of Philosophy (PhD)
Biochemistry & Molecular Biology
Moorthy P. Ponnusamy
A myriad of genetic and other abnormal changes underlies the aggressiveness and dissemination properties observed in pancreatic cancer (PC). Aberrant protein glycosylation is a commonly observed feature in PC. The modification of protein O-glycosylation is mediated by glycosyltransferases, which attach and sequentially elongate monosaccharides on Serine/Threonine (Ser/Thr) motifs. Aberrant glycosylation is recognized as an emerging hallmark of cancer where a disruption in normal glycosylation results in irregular O-glycans.
This dissertation research has investigated the consequences of aberrant protein glycosylation on stemness and enhancement of metastatic properties in pancreatic ductal adenocarcinoma (PDAC). Several publications have reported aberrant O-glycosylation increases in oncogenic and aggressive properties of cancer. My thesis is primarily focused on delineating the mechanistic underpinnings of aberrant protein O-glycosylation’s effects on stemness and metastatic properties. We identified a unique glycosylation makeup present on proteins attributed to a loss in C1GALT1 (Core-1 O-glycans) expression. In addition, we identified differential expression of glycosyltransferases attributed by GCNT3 and B3GNT3 for preferential organ-specific PC metastasis.
My first set of results addresses the effects that aberrant O-glycosylation has on the proteins that harbor them. A proteomic screen in PC cells enriched with truncated O-glycans (Tn-antigens) identified differentially glycosylated CD44 due to a loss in C1GALT1 expression. Additionally, loss in C1GALT1 expression resulted in an increased stemness and tumorigenesis, detected using in vitro and in vivo analysis, which were compounded due to a concomitant loss in C1GALT1/CD44 expression, which reversed the effects.
We further investigate the role that altered glycosylation has on organ-specific metastasis. Using PC cell lines with liver and lung-derived metastasis, a glycosyltransferase expressional array identified an increased fold change with inverse fold changes for GCNT3 and B3GNT3 in the liver- and lung-derived PC cells, respectively. We confirmed our analysis using multiple in vitro analyses (RT-PCR, ddPCR, western blot, and immunohistochemistry) to confirm expressional variation in several PC cell lines.
Overall, my work contextualized the diverse role aberrant glycosylation has on protein function in PC. The unique mechanisms I discovered begin to provide a potential mode of action to develop therapeutics for cancer stem cells and metastasis.
Leon, Frank, "Molecular Mechanisms of Aberrant Protein Glycosylation in Pancreatic Cancer Stemness and Metastasis" (2021). Theses & Dissertations. 605.