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R-spondins are a family of secreted Wnt agonists. One of the family members, R-spondin 2 (RSPO2), has an important role in embryonic development, bone formation and myogenic differentiation; however, its role in human cancers remains largely unknown. Here we show that RSPO2 expression is downregulated in human colorectal cancers (CRCs) due to promoter hypermethylation, and that the RSPO2 reduction correlates with tumour differentiation, size and metastasis. Overexpression of RSPO2 suppresses CRC cell proliferation and tumorigenicity, whereas the depletion of RSPO2 enhances tumour cell growth. RSPO2 has an inhibitory effect on Wnt/β-catenin signaling in the CRC cells that show suppressed cell proliferation. In human CRC cells, the RSPO2-induced inhibition of Wnt signaling depends on leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5); RSPO2 interacts with LGR5 to stabilize the membrane-associated zinc and ring finger 3 (ZNRF3). Our data suggest that RSPO2 functions as a tumour suppressor in human CRCs, and these data reveal a RSPO2-induced, LGR5-dependent Wnt signaling-negative feedback loop that exerts a net growth-suppressive effect on CRC cells.

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Summary The security of space information network (SIN) is getting more and more important now. Because of the special features of SIN (e.g., the dynamic and unstable topology, the highly exposed links, the restricted computation power, the flexible networking methods, and so on), the security protocol for SIN should have a balance between security properties and computation/storage overhead. Although a lot of security protocols have been proposed recently, few can provide overall attacks resistance power with low computation and storage cost. To solve this problem, in this paper we propose a lightweight authentication scheme for space information network. It is mainly based on the self‐updating strategy for user's temporary identity. The scheme consists of two phases, namely, the registration phase and the authentication phase. All the computing operations involved are just hash function (h), the bit‐wise exclusive‐or operation (⊕), and the string concatenation operation (||), which are of low computation cost. The security properties discussion and the attacks–resistance power analysis show that the proposed authentication scheme can defend against various typical attacks, especially denial of service attacks. It is sufficiently secure with the lowest computation and storage costs. Furthermore, the formal security proof in SVO logic also demonstrates that the scheme can satisfy the security goals very well. Copyright © 2016 John Wiley & Sons, Ltd.

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