State Key Laboratory for Liver Research, University of Hong Kong; Department of Pathology, University of Hong Kong.
J Pathol. 2014 May;233(1):51-60. doi: 10.1002/path.4319. Epub 2014 Jan 27.
Loss of mitotic checkpoint of cells contributes to chromosomal instability and leads to carcinogenesis. Mitotic arrest deficient 1 (MAD1) is a key component in mitotic checkpoint signalling. In this study, we identified a novel MAD1 interacting partner, proline-rich acidic protein 1 (PRAP1), using yeast-two hybrid screening, and investigated its role in mitotic checkpoint signalling in hepatocellular carcinoma (HCC). We demonstrated the physical interaction of PRAP1 with MAD1 and of PRAP1 with MAD1 isoform MAD1β, using a co-immunoprecipitation assay. Moreover, stable expression of PRAP1 in mitotic checkpoint-competent HCC cells, BEL-7402 and SMMC-7721, induced impairment of the mitotic checkpoint (p < 0.01), formation of chromosome bridges (p < 0.01) and aberrant chromosome numbers (p < 0.001). Interestingly, ectopic expression PRAP1 in HCC cells led to significant under-expression of MAD1. In human HCC tumours, 40.4% (23/57) of HCCs showed under-expression of PRAP1 protein as compared with their corresponding non-tumorous livers; up-regulation of MAD1 protein was significantly associated with down-regulation of PRAP1 (p = 0.030). Our data revealed that PRAP1 is a protein interacting partner of MAD1 and that PRAP1 is able to down-regulate MAD1 and suppress mitotic checkpoint signalling in HCC.
细胞有丝分裂检查点的丧失导致染色体不稳定，从而引发癌变。有丝分裂阻滞缺陷 1（MAD1）是有丝分裂检查点信号转导的关键组成部分。在这项研究中，我们使用酵母双杂交筛选鉴定了一个新的 MAD1 相互作用伙伴脯氨酸丰富酸性蛋白 1（PRAP1），并研究了其在肝癌（HCC）中的有丝分裂检查点信号转导中的作用。我们通过共免疫沉淀实验证实了 PRAP1 与 MAD1 和 MAD1 同工型 MAD1β的物理相互作用。此外，在有丝分裂检查点功能完整的 HCC 细胞 BEL-7402 和 SMMC-7721 中稳定表达 PRAP1 会导致有丝分裂检查点受损（p < 0.01）、染色体桥形成（p < 0.01）和染色体数目异常（p < 0.001）。有趣的是，在 HCC 细胞中异位表达 PRAP1 会导致 MAD1 的表达显著下调。在人类 HCC 肿瘤中，与相应的非肿瘤肝脏相比，40.4%（23/57）的 HCC 表现出 PRAP1 蛋白表达下调；MAD1 蛋白的上调与 PRAP1 的下调显著相关（p = 0.030）。我们的数据表明，PRAP1 是 MAD1 的蛋白质相互作用伙伴，并且 PRAP1 能够下调 MAD1 并抑制 HCC 中的有丝分裂检查点信号转导。
