Placental malaria infection is mediated by the binding of the malarial VAR2CSA protein to the placental glycosaminoglycan, chondroitin sulfate. Recombinant subfragments of VAR2CSA (rVAR2) have also been shown to bind specifically and with high affinity to cancer cells and tissues, suggesting the presence of a shared type of oncofetal chondroitin sulfate (ofCS) in the placenta and in tumors. However, the exact structure of ofCS and what determines the selective tropism of VAR2CSA remains poorly understood. In this study, ofCS was purified by affinity chromatography using rVAR2 and subjected to detailed structural analysis. We found high levels of N-acetylgalactosamine 4-O-sulfation (∼80-85%) in placenta- and tumor-derived ofCS. This level of 4-O-sulfation was also found in other tissues that do not support parasite sequestration, suggesting that VAR2CSA tropism is not exclusively determined by placenta- and tumor-specific sulfation. Here, we show that both placenta and tumors contain significantly more chondroitin sulfate moieties of higher molecular weight than other tissues. In line with this, CHPF and CHPF2, which encode proteins required for chondroitin polymerization, are significantly upregulated in most cancer types. CRISPR/Cas9 targeting of CHPF and CHPF2 in tumor cells reduced the average molecular weight of cell-surface chondroitin sulfate and resulted in a marked reduction of rVAR2 binding. Finally, utilizing a cell-based glycocalyx model, we showed that rVAR2 binding correlates with the length of the chondroitin sulfate chains in the cellular glycocalyx. These data demonstrate that the total amount and cellular accessibility of chondroitin sulfate chains impact rVAR2 binding and thus malaria infection.

中文翻译：

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疟疾 VAR2CSA 蛋白对硫酸软骨素的特异性取决于 4-O-硫酸化和配体可及性。

胎盘疟疾感染是由疟疾 VAR2CSA 蛋白与胎盘糖胺聚糖、硫酸软骨素结合介导的。VAR2CSA (rVAR2) 的重组亚片段也已显示与癌细胞和组织特异性结合并具有高亲和力，这表明胎盘和肿瘤中存在共同类型的癌胎儿硫酸软骨素 (ofCS)。然而，对于 CS 的确切结构以及决定 VAR2CSA 选择性趋向性的因素仍然知之甚少。在这项研究中，ofCS 使用 rVAR2 通过亲和层析进行纯化，并进行详细的结构分析。我们在胎盘和肿瘤来源的 CS 中发现了高水平的 N-乙酰半乳糖胺 4-O-硫酸化（~80-85%）。在不支持寄生虫隔离的其他组织中也发现了这种水平的 4-O-硫酸化，表明 VAR2CSA 向性并不完全由胎盘和肿瘤特异性硫酸化决定。在这里，我们表明胎盘和肿瘤都含有比其他组织更多的更高分子量的硫酸软骨素部分。与此一致，编码软骨素聚合所需蛋白质的 CHPF 和 CHPF2 在大多数癌症类型中显着上调。CRISPR/Cas9 靶向肿瘤细胞中的 CHPF 和 CHPF2 降低了细胞表面硫酸软骨素的平均分子量，并导致 rVAR2 结合显着降低。最后，利用基于细胞的糖萼模型，我们发现 rVAR2 结合与细胞糖萼中硫酸软骨素链的长度相关。