Functional analysis of a novel follistatin-like molecule in gastrointestinal lesion.

我们从胃成纤维细胞中分离出一个编码新蛋白的基因，该蛋白含有两个卵泡抑素模块，可能结合TGF β相关生长因子和一个与EGF/神经调节蛋白（NRG）家族生长因子密切相关的表皮生长因子（EGF）样结构域。序列分析发现了新的cDNA克隆，其蛋白产物被命名为tomoregulin (TR)，由至少三个同工异构体组成，这些异构体的细胞质结构域可以区分。所有同工型的细胞质结构域都很短，与序列预测一致，并且含有潜在的g蛋白激活基序。TR前体（Pro-TR）是糖基化的跨膜蛋白。由蛋白水解裂解产生的两种分泌的可溶性形式通过存在或不存在egf样结构域来区分。与EGF/NRG家族生长因子相比，TR的EGF样结构域高度保守，但在第39位（Arg->His 39）有一个精氨酸向组氨酸的取代。Arg39已被证明对EGF中的受体识别至关重要。与这一假设相一致的是，纯化的可溶性TR胞外结构域在某些细胞系中未能激活EGF受体、erbB-2和erbB-3，表明TR不是它们的配体。然而，在mkn28胃癌细胞中，可溶性TR刺激erbB-4酪氨酸磷酸化，尽管与神经调节蛋白诱导的erbB-4酪氨酸磷酸化相比较弱；这表明TR可能是erbB-4或erbB-4相关受体酪氨酸激酶的配体。TR可能在胚胎中晚期的正常发育和成人中枢神经系统组织的维持中发挥重要作用，因为在这些组织中观察到高表达的TR mrna。模块化的特点为TR提供了多种角色；这些功能包括作为erbb受体的配体，通过卵泡抑素模块直接相互作用调节TGF β相关生长因子信号，以及g蛋白偶联受体。

We have isolated a gene from stomach fibroblasts encoding novel proteins containing two follistatin modules which might bind TGF β-related growth factors and a single epidermal growth factor (EGF)-like domain which is closely related to EGF/Neuregulin (NRG) family growth factors. Sequence analysis revealed novel cDNA clones, the protein products of which were designated tomoregulin (TR) and consisted of at least three isoforms which were distinguished by their cytoplasmic domains. The cytoplasmic domains in all isoforms were short, as predicted from the sequences, and contained potential G-protein activating motifs. Precursors of TR (Pro-TR) are glycosylated transmembrane proteins. Two secreted soluble forms resulted from proteolytic cleavage were distinguished by the presence or absence of the EGF-like domain. The EGF-like domain of TR was highly conserved compared to EGF/NRG family growth factors with the exception of an arginine to histidine substitution at position 39 (Arg->His 39). Arg39 has been shown to be essential for receptor recognition in EGF.Consistent with this hypothesis, the purified soluble TR extracellular domain failed to activate the EGF receptor, erbB-2 and erbB-3 in certain cell lines, indicating TR was not a ligand for them. However, in MKN 28 gastric cancer cells, soluble TR stimulated erbB-4 tyrosine phosphorylation, although it was weak compared to neuregulin-induced erbB-4 tyrosine phosphorylation ; this suggests that TR might be a ligand for erbB-4 or erbB-4 related receptor tyrosine kinase. TR may have important roles in normal development of middle to late stages of embryos and maintenance of adult central nervous system tissues as high expression of TR mRNAs was observed in these tissues. The modular features suggest multiple roles for TR ; these include functioning as a ligand for erbB-receptor, a regulator of TGF β-related growth factor signaling by direct interaction through the follistatin modules, and a G-protein coupled receptor.