Oncofetal Chondroitin Sulfate Glycosaminoglycans Are Key Players in Integrin Signaling and Tumor Cell Motility

Abstract

Many tumors express proteoglycans modified with oncofetal chondroitin sulfate glycosaminoglycan chains (ofCS), which are normally restricted to the placenta. However, the role of ofCS in cancer is largely unknown. The function of ofCS in cancer was analyzed using the recombinant ofCS-binding VAR2CSA protein (rVAR2) derived from the malaria parasite, Plasmodium falciparum. We demonstrate that ofCS plays a key role in tumor cell motility by affecting canonical integrin signaling pathways. Binding of rVAR2 to tumor cells inhibited the interaction of cells with extracellular matrix (ECM) components, which correlated with decreased phosphorylation of Src kinase. Moreover, rVAR2 binding decreased migration, invasion and anchorage-independent growth of tumor cells in vitro. Mass spectrometry of ofCS-modified proteoglycan complexes affinity purified from tumor cell lines on rVAR2 columns, revealed an overrepresentation of proteins involved in cell motility and integrin signaling, such as integrin β1 (ITGB1) and integrin α4 (ITGA4). Saturating concentrations of rVAR2 inhibited downstream integrin signaling, which was mimicked by knockdown of the core CS synthesis enzymes Beta-1,3-Glucuronyltransferase 1 (B3GAT1) and Chondroitin Sulfate N-Acetylgalactosaminyltransferase 1 (CSGALNACT1). The ofCS modification was highly expressed in both human and murine metastatic lesions in situ and pre-incubation or early intravenous treatment of tumor cells with rVAR2 inhibited seeding and spreading of tumor cells in mice. This was associated with a significant increase in survival of the animals. These data functionally link ofCS modifications with cancer cell motility and further highlights ofCS as a novel therapeutic cancer target. Implications The cancer specific expression of oncofetal chondroitin sulfate aids in metastatic phenotypes and is a candidate target for therapy.

NG2 Proteoglycan Enhances Brain Tumor Progression by Promoting Beta-1 Integrin Activation in both Cis and Trans Orientations

“…Similar results were obtained with the NG2-negative human U251 glioma cell line following expression of full-length rat NG2 [3]. Although glycosaminoglycan chains are often important for proteoglycan function [29,30], we have not detected a role for the single NG2 chondroitin sulfate chain in NG2 interaction with integrins, suggesting that the interaction is protein-protein in nature. We also used U251 cells to investigate changes in cell biology that are caused by forced expression of several key NG2 variants [7,8].…”

Premetastatic niches, exosomes and circulating tumor cells: Early mechanisms of tumor dissemination and the relation to surgery

“…Interestingly, in a lung cancer model, oncostatin knock‐out mice had reduced CTC, fewer lung metastases and increased overall survival . Furthermore, proteoglycans have been shown to be extensively involved in the migration of tumor cells as demonstrated by Chondroitin Sulfate A that mediates focal adhesion and motility, while blocking Chondroitin Sulfate A inhibited cellular migration and metastasis formation …”

Burkitt lymphoma expresses oncofetal chondroitin sulfate without being a reservoir for placental malaria sequestration

“…The pull downs were performed as in Ref. 44. In short, BLderived cells were washed in cold PBS and treated with cell lysis buffer (150 mM NaCl, 50 mM tris(hydroxymethyl)aminomethane hydrochloride (Tris-HCl), 2.5 mM MgCl 2 , 1 mM ethylenediaminetetraacetic acid (EDTA), 1% 3-((3-cholamidopropyl) dimethylammonio)21-propanesulfonate (CHAPS) and protease and phosphatase inhibitor cocktails (Roche)).…”

“…4) As we have recently described, rVAR2 ofCS-specific pull down from cell lysates revealed a number of proteins that included ofCS substituted CSPGs as well as several known CSPG interaction partners, such as integrins. 44 To attempt to get an overview over the connection between all the hits as well as how they relate to cellular functions and disease processes in BL, the identified hits were subjected to ingenuity pathway analysis (IPA). This shows an involvement of ofCS in several immune pathways, and in processes related to the development of immunological diseases ( Supporting Information, Fig.…”