Advisory Committee Chair
Mythreye Karthikeyan
Advisory Committee Members
Eason Hildreth
Doug Hurst
Chander Raman
Ralph Sanderson
Document Type
Dissertation
Date of Award
2023
Degree Name by School
Doctor of Philosophy (PhD) Heersink School of Medicine
Abstract
Proteoglycans (PG) are defined as proteins with one or more covalently bound polysaccharides called glycosaminoglycan chains (GAG). PGs can either be present on the cell surface or in the extracellular matrix to mediate cellular homeostasis in normal physiology as well as exert profound roles in diseases such as cancer. PGs can interact with a host of proteins such as growth factors through their core protein and/or their GAG chains, serving as an accessory receptor to mediate signaling by binding to the ligands and altering ligand-signaling receptor binding, defined as a co-receptor function. Developmentally and in pathologies like cancer, TGF-β signaling plays a crucial role, in which PG co-receptor roles are vital for tumor progression. Betaglycan/type III TGF-β receptor (TβRIII) is an established PG co-receptor for the TGF-β superfamily with direct binding demonstrated for TGF-β 1-3 and inhibin A. BG is modified at the serine residues S534 and S545 in humans, to which heparan sulfate and chondroitin sulfate chains are covalently attached. While BG has the highest affinities for TGF-βs, other PGs such as SDC and CD44 have been shown to bind TGF-β and activate signaling in multiple systems. PGs can also be cleaved from the cell surface to release the ectodomain portion in a process called ectodomain shedding, a feature indispensable for the regulation of TGF-β signaling and the cells' responses to TGF-β. Dysregulated shedding of PGs is commonly associated with various pathologies including cancer. The role of betaglycan shedding and its role iniii ovarian cancer biology remains to be elucidated. Here, we examine the specific roles and contributions of PG forms of betaglycan on ectodomain shedding and TGF-β signaling in ovarian cancer biology. To accomplish this, a combination of site-directed mutagenesis along with overexpression, knockdown, and CRISPR models in ovarian cancer cells, as well as unbiased transcriptomics and protein arrays were used to identify mechanisms of shedding. In addition, a series of in vitro cell biological assays and TGF-β signaling readouts were employed. Using these approaches, I determined that compared to modified BG-expressing cells, unmodified (ΔGAG) expressing cells had reduced ectodomain shedding, mediated by a novel regulator of BG shedding, TIMP3. TIMP3 expression was found to be differentially expressed in cells that expressed different forms of BG. Particularly, ΔGAG-expressing cells had higher levels of TIMP3. A decrease in shedding of BG led to increased TGF-β signaling and promoted ovarian cancer cell invasion. Notably, we found modified soluble-betaglycan in the ascites fluid of patients with ovarian cancer. We found the concentration of shed-BG positively correlated with disease stage and negatively correlated with patient survival. These studies demonstrate the underappreciated significance of the part-time nature of BG and the impact of the PG form of BG in its shedding and TGF-β signaling responses crucial for understanding TGF- β signaling dynamics.
Recommended Citation
Choi, Alex Kwon-Bowers, "Role Of Proteoglycan Forms Of The Type Iii Tgf-Β Receptor/Betaglycan In Tgf-Β Signaling In Ovarian Cancer Models" (2023). All ETDs from UAB. 3488.
https://digitalcommons.library.uab.edu/etd-collection/3488