De Winter J P, De Vries C J, Van Achterberg T A, Ameerun R F, Feijen A, Sugino H, De Waele P, Huylebroeck D, Verschueren K, Van Den Eijden-Van Raaij A J
Hubrecht Laboratory, Netherlands Institute for Development Biology, Utrecht.
Exp Cell Res. 1996 May 1;224(2):323-34. doi: 10.1006/excr.1996.0142.
Truncated activin type II receptors have been reported to inhibit activin receptor signaling in Xenopus embryos, although the mechanism of action for this effect has not been fully understood. In the present study we demonstrate that in P19 embryonal carcinoma cells both the induction of the activin responsive 3TP-lux reporter construct and the inhibition of retinoic acid-induced neuronal differentiation by activin are blocked by expression of a truncated activin receptor. To reveal the mechanism of action of truncated activin receptors, the interaction between different activin receptors has been investigated upon coexpression in COS cells followed by cross-linking of 125I-activin A and subsequent immunoprecipitation. Complexes between a truncated activin type IIA receptor and activin type IA and type IB receptors can be formed, as demonstrated by coimmunoprecipitation of these type I receptors with the truncated activin type IIA receptor. Other type I receptors known as ALK-1 and ALK-6 also coimmunoprecipitate with the truncated type IIA receptor, whereas ALK-3 and ALK-5 do not. Furthermore, the activin type IIB2 receptor does not coimmunoprecipitate with the truncated type IIA receptor, but decreases activin binding to the truncated type IIA receptor. In double immunoprecipitation experiments with cell lysates from COS cells, in which full-length activin type IIA and type IIB2 receptors were cotransfected, no interaction between these receptors was found. In contrast, homomeric complexes of full-length activin type IIA receptors were detected. These results implicate that truncated activin receptors can interfere with activin signaling by interacting with activin type I receptors. Additionally, truncated activin type IIB2 receptors might also interfere with type IIA receptor signaling by decreasing activin binding to the type IIA receptor and therefore might be more potent in inhibiting activin signal transduction. Furthermore, our data indicate that truncated type IIA receptors can interact with other type I receptors and as such might inhibit signal transduction by type I receptors other than activin type IA and type IB receptors.
据报道，截短的激活素II型受体可抑制非洲爪蟾胚胎中的激活素受体信号传导，尽管这种效应的作用机制尚未完全明确。在本研究中，我们证明，在P19胚胎癌细胞中，截短的激活素受体的表达可阻断激活素应答性3TP-lux报告基因构建体的诱导以及激活素对维甲酸诱导的神经元分化的抑制作用。为了揭示截短的激活素受体的作用机制，我们在COS细胞中共表达不同的激活素受体，然后对125I-激活素A进行交联并随后进行免疫沉淀，研究了它们之间的相互作用。截短的激活素IIA型受体与激活素IA型和IB型受体之间可形成复合物，这通过这些I型受体与截短的激活素IIA型受体的共免疫沉淀得以证明。其他已知的I型受体，如ALK-1和ALK-6，也与截短的IIA型受体共免疫沉淀，而ALK-3和ALK-5则不然。此外，激活素IIB2型受体不与截短的IIA型受体共免疫沉淀，但会减少激活素与截短的IIA型受体的结合。在用COS细胞裂解物进行的双重免疫沉淀实验中，全长激活素IIA型和IIB2型受体共转染，未发现这些受体之间存在相互作用。相反，检测到了全长激活素IIA型受体的同源复合物。这些结果表明，截短的激活素受体可通过与激活素I型受体相互作用来干扰激活素信号传导。此外，截短的激活素IIB2型受体也可能通过减少激活素与IIA型受体的结合来干扰IIA型受体信号传导，因此在抑制激活素信号转导方面可能更有效。此外，我们的数据表明，截短的IIA型受体可与其他I型受体相互作用，因此可能抑制除激活素IA型和IB型受体之外的I型受体的信号转导。
