Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, Texas 76019, USA.
Biochemistry. 2011 Jun 28;50(25):5731-42. doi: 10.1021/bi200347y. Epub 2011 Jun 2.
Our study showed that a combination of 6-thiopurine (6-TP) drugs and a redox agent effectively inhibits the motility of SUM cells derived from human inflammatory breast cancer (IBC) cells and RhoC-overexpressed mammary epithelium cells. This 6-TP-mediated inhibition of cell motility occurs because the treated 6-TPs target and inactivate RhoC. A molecular mechanism for inactivation by the 6-TP-mediated RhoC is proposed by which treated TPs are converted in cells into 6-thioguanosine phosphate (6-TGNP). This 6-TGNP in turn reacts with the Cys(20) side chain of the redox-sensitive GXXXCGK(S/T)C motif of RhoC to produce a 6-TGNP-RhoC disulfide adduct. A redox agent synergistically enhances the formation process of this disulfide. The adduct that is formed impedes RhoC guanine nucleotide exchange, which populates an inactive RhoC. Our results suggest that 6-TGNP can also react with the redox-sensitive GXXXCGK(S/T)C and GXXXXGK(S/T)C motif of RhoA and Rac, respectively, to produce a 6-TGNP-RhoA and 6-TGNP-Rac disulfide adduct. However, given that RhoC has been shown to be overexpressed in ∼90% of IBC lesions, the populated RhoC but not other Rho proteins is likely to be a primary target for 6-TPs and a redox agent to terminate the metastasis of IBC.
我们的研究表明，6-硫代嘌呤（6-TP）药物与氧化还原剂的联合使用可有效抑制源自人类炎症性乳腺癌（IBC）细胞和 RhoC 过表达乳腺上皮细胞的 SUM 细胞的迁移。这种 6-TP 介导的细胞迁移抑制作用是由于被处理的 6-TP 靶向并失活 RhoC 所致。提出了一种 6-TP 介导的 RhoC 失活的分子机制，其中被处理的 TPs 在细胞内转化为 6-硫代鸟苷磷酸（6-TGNP）。这种 6-TGNP 反过来与 RhoC 的氧化还原敏感的 GXXXCGK（S/T）C 基序中的 Cys（20）侧链反应，产生 6-TGNP-RhoC 二硫键加合物。氧化还原剂协同增强了该二硫键形成过程。形成的加合物阻碍了 RhoC 鸟嘌呤核苷酸交换，从而使 RhoC 处于非活性状态。我们的研究结果表明，6-TGNP 还可以分别与 RhoA 和 Rac 的氧化还原敏感的 GXXXCGK（S/T）C 和 GXXXXGK（S/T）C 基序反应，生成 6-TGNP-RhoA 和 6-TGNP-Rac 二硫键加合物。然而，鉴于 RhoC 已被证明在约 90%的 IBC 病变中过表达，被占据的 RhoC 而不是其他 Rho 蛋白可能是 6-TP 和氧化还原剂终止 IBC 转移的主要靶标。
