Lorenzi M V, Castagnino P, Chen Q, Hori Y, Miki T
Laboratory of Cellular and Molecular Biology, National Cancer Institute, Building 37 Room 1E24, 37 Convent Dr. MSC 4255, Bethesda, Maryland 20892, USA.
Oncogene. 1999 Aug 19;18(33):4742-55. doi: 10.1038/sj.onc.1202851.
A search for transforming genes expressed in brain led to the identification of a novel isoform of Ost, an exchange factor for RhoA and Cdc42. In addition to the Dbl-homology (DH) and pleckstrin-homology (PH) domains identified in the original Ost, this isoform contained a SH3 domain and a novel HIV-Tat related (TR) domain. The presence or absence of these domains in Ost defined multiple isoforms of the protein. RT - PCR and in situ hybridization analysis revealed that these isoforms were generated by tissue-specific and developmentally restricted alternative splicing events. Whereas deletion of the N-terminus activated the transforming properties of Ost, the presence of the SH3 domain reduced the transforming activity of the protein. This inhibition was relieved by the presence of a TR domain, which contained a potential SH3 ligand sequence. The transforming activity of all Ost isoforms was inhibited by dominant negative forms of the Rho family proteins. Expression of Ost isoforms potently induced the formation of actin stress fibers and filopodia as well as JNK activity and AP1- and SRF-regulated transcriptional pathways. Ost transfectants also displayed elevated levels of cyclins A and D1, suggesting that the de-regulation of these cyclins is linked to Ost-mediated transformation.
对大脑中表达的转化基因进行的搜索，导致鉴定出一种新型的Ost异构体，它是RhoA和Cdc42的交换因子。除了在原始Ost中鉴定出的Dbl同源（DH）和普列克底物蛋白同源（PH）结构域外，这种异构体还包含一个SH3结构域和一个新型的HIV-Tat相关（TR）结构域。Ost中这些结构域的存在与否定义了该蛋白的多种异构体。逆转录-聚合酶链反应（RT-PCR）和原位杂交分析表明，这些异构体是由组织特异性和发育受限的可变剪接事件产生的。虽然N端的缺失激活了Ost的转化特性，但SH3结构域的存在降低了该蛋白的转化活性。TR结构域（包含一个潜在的SH3配体序列）的存在缓解了这种抑制作用。所有Ost异构体的转化活性都受到Rho家族蛋白显性负性形式的抑制。Ost异构体的表达强烈诱导肌动蛋白应力纤维和丝状伪足的形成，以及JNK活性和AP1及SRF调节的转录途径。Ost转染细胞还显示细胞周期蛋白A和D1水平升高，表明这些细胞周期蛋白的失调与Ost介导的转化有关。
