Expression and functions of semaphorins in cancer
Semaphorins are a large family of genes involved in the development and morphogenesisof nervous system. Through the interactions with and the signaling to their downstream receptors,semaphorins are able to regulate cell growth and cytoskeleton assembly. Furthermore, a growing body ofevidence has indicated that semaphorins are important regulators of immune responses and angiogenesis,which are usually dysregulated and associated with tumorigenic processes. The expression levels of severalsemaphorins in tumors have been shown significantly different in a tissue-specific manner. For example, theexpression of SEMA5A was down-regulated in lung adenocarcinoma, but not in other cancers. SEMA5Ademonstrated oncogenic effects in gastric and pancreatic cancers, but showed tumor suppressive functions inlung carcinoma and glioma cells. Similarly, many other semaphorins show both tumor promoting and tumorsuppressor functions. To clarify the influences of semaphorins, we review the current status of semaphorinswith a focus on their expression levels and function effects in cancers.