VAMP/synaptobrevin-associated protein B (VAP-B) is a type II ER membrane protein, but its N-terminal MSP domain (MSPd) can be cleaved and secreted. Mutations preventing the cleavage and secretion of MSPd have been implicated in cases of human neurodegenerative diseases. The site of VAP cleavage and the tissues capable in releasing the processed MSPd are not understood. In this study, we analyze the C. elegans VAP-B homolog, VPR-1, for its processing and secretion from the intestine. We show that intestine-specific expression of an N-terminally FLAG-tagged VPR-1 rescues underdeveloped gonad and sterility defects in vpr-1 null hermaphrodites. Immunofluorescence studies reveal that the tagged intestinal expressed VPR-1 is present at the distal gonad. Mass spectrometry analysis of a smaller product of the N-terminally tagged VPR-1 identifies a specific cleavage site at Leu156. Mutation of the leucine results in loss of gonadal MSPd signal and reduced activity of the mutant VPR-1. Thus, we report for the first time the cleavage site of VPR-1 and provide direct evidence that intestinally expressed VPR-1 can be released and signal in the distal gonad. These results establish the foundation for further exploration of VAP cleavage, MSPd secretion, and non-cell-autonomous signaling in development and diseases.

VAMP/synaptobrevin 相关蛋白 B (VAP-B) 是一种 II 型 ER 膜蛋白，但其 N 端 MSP 结构域 (MSPd) 可以被切割和分泌。阻止 MSPd 切割和分泌的突变与人类神经退行性疾病有关。VAP 裂解位点和能够释放加工过的 MSPd 的组织尚不清楚。在这项研究中，我们分析了秀丽隐杆线虫VAP-B 同源物 VPR-1 的加工和肠道分泌。我们展示了 N 末端 FLAG 标记的 VPR-1 的肠道特异性表达挽救了vpr-1中不发达的性腺和不育缺陷空雌雄同体。免疫荧光研究表明，标记的肠道表达的 VPR-1 存在于远端性腺中。对 N 末端标记的 VPR-1 的较小产物的质谱分析确定了 Leu156 处的特定切割位点。亮氨酸的突变导致性腺 MSPd 信号的丢失和突变 VPR-1 的活性降低。因此，我们首次报道了 VPR-1 的切割位点，并提供了直接证据表明肠道表达的 VPR-1 可以在远端性腺中释放和发出信号。这些结果为进一步探索发育和疾病中的 VAP 裂解、MSPd 分泌和非细胞自主信号传导奠定了基础。