Sulfated glycosaminoglycans mediate prion-like behavior of p53 aggregates

Sulfated glycosaminoglycans (GAGs) such as heparan sulfate (HS) are heteropolysaccharides implicated in the pathology of protein aggregation diseases including localized and systemic forms of amyloidosis. Among subdomains of sulfated GAGs, highly sulfated domains of HS, called HS S-domains, have been highlighted as being critical for HS function in amyloidoses. Recent studies suggest that the tumor suppressor p53 aggregates to form amyloid fibrils and propagates in a prion-like manner; however, molecules and mechanisms that are involved in the prion-like behavior of p53 aggregates have not been addressed. Here, we identified sulfated GAGs as molecules that mediate prion-like behavior of p53 aggregates. Sulfated GAGs at the cell surface were required for cellular uptake of recombinant and cancer cell-derived p53 aggregates and extracellular release of p53 from cancer cells. We further showed that HS S-domains accumulated within p53 deposits in human ovarian cancer tissues, and enzymatic remodeling of HS S-domains by Sulf-2 extracellular sulfatase down-regulated cellular uptake of p53 aggregates. Finally, sulfated GAG-dependent cellular uptake of p53 aggregates was critical for subsequent extracellular release of the aggregates and gain of oncogenic function in recipient cells. Our work provides a mechanism of prion-like behavior of p53 aggregates and will shed light on sulfated GAGs as a common mediator of prions.

Glycosaminoglycans (GAGs) are linear, unbranched polysaccharides that are attached to a core protein to form proteoglycans. The GAG chain structure is heterogeneous and can vary in net charges. Sulfated GAGs, such as heparan sulfate (HS) and chondroitin sulfate (CS), consist of repeating disaccharide units of a uronic acid and either N-acetylglucosamine or N-acetylgalactosamine. The structural diversity of GAGs confers binding selectivity of GAGs to their ligands and, thereby, plays an essential part in the functions of proteoglycans including organogenesis, signal transduction, and inflammation. Sulfated GAGs have also been implicated in the pathology of several diseases such as cancer and amyloidosis, which is the most common protein aggregation disease (1–3). Since the identification of sulfated GAGs as a common constituent of amyloid deposits in systemic and localized amyloidoses (4), sulfated GAGs have been established to affect the pathogenesis and progression of amyloidoses by promoting the formation and cellular interaction of protein aggregates (1).The human TP53 gene encodes a nuclear tumor suppressor—p53—that can also respond to several stress conditions to induce cell cycle arrest and apoptosis (5). TP53 gene mutations occur in more than 50% of human cancers, which makes it the most common mutant gene in cancers. The DNA-binding domain of p53 is conformationally unstable (6), and several hotspot mutants are reportedly unfolded (7). p53 was recently reported to form protein aggregates in human cancer tissues and in vitro (8–11), which suggests that p53-mutant cancers may be a new class of protein aggregation diseases. p53 aggregates were proposed to demonstrate prion-like behavior like that of many other protein aggregates (12). We and others reported that the patterns and degrees of GAG’s sulfation modification (13–16), especially the highly sulfated domains of HS (HS S-domains), are essential for the pathology and progression of systemic and localized amyloidoses. However, the involvement of sulfated GAGs in transcellular propagation of p53 aggregates must still be elucidated.Ovarian cancer is often diagnosed at an advanced stage, and little progress has been achieved in chemotherapy treatment (17). Alterations in the TP53 gene are quite prevalent in ovarian cancer, especially in the most common histological subtype—high-grade serous ovarian carcinoma (96%) (18)—which supports the pathological significance of p53 mutations. In our study here, we investigated the accumulation of HS S-domains in ovarian cancer tissues and the involvement of sulfated GAGs in extracellular release and cellular interaction of p53 aggregates. HS S-domains can be postsynthetically remodeled by Sulf-2 extracellular sulfatase (19). In addition, we studied whether enzymatic remodeling of HS S-domains would affect cellular uptake of extracellularly released p53. Our study supports the common roles of GAGs and their sulfation modifications in transcellular propagation of various protein aggregates.