Nuclear localization of Dpc4 (Madh4, Smad4) in colorectal carcinomas and relation to mismatch repair/transforming growth factor-β receptor defects
Nuclear localization of Dpc4 (Madh4, Smad4) in colorectal carcinomas and relation to mismatch repair/transforming growth factor-β receptor defects
复制标题
DOI：
10.1016/s0002-9440(10)63995-8
复制
发表时间：
2001-02-01
影响因子：
6
通讯作者：
Kern, SE
中科院分区：
文献类型：
--
作者：
Montgomery, E;Goggins, M;Kern, SE
肿瘤抑制蛋白Dpc 4（Smad 4，Madh 4）调节基因表达。在广泛转化生长因子（TGF）超家族的细胞外配体与其同源受体复合物结合时，潜在的细胞质DPC 4被激活并移位到细胞核中以作为各种DNA结合转录激活因子复合物的一部分起作用。控制DPC 4的肿瘤抑制功能的最相关的配体/受体对仍然不确定，但通常认为是TGF-β及其异聚体受体。我们利用一个偶然的自然实验来直接验证这个假设：在几乎所有具有微卫星不稳定性的结直肠癌中，如在遗传性非息肉病性结直肠癌（HNPCC）和散发性髓样结直肠癌中所见，TGF-β II型受体基因因突变而失活。我们使用特异且敏感的DPC 4免疫组织化学标记，检测了13例HNPCC中DPC 4的核定位，6例髓样癌和41例散发性非髓样结直肠癌。与发表的比率一致，41例散发性肿瘤中有2例（5%）显示DPC 4蛋白完全丢失，表明遗传失活。所有13例HNPCC和6例髓样肿瘤均具有完整的胞浆和核DPC 4定位。对来自HNPCC患者的三种癌症中的TGFBR 2基因进行测序，并且所有这些癌症都具有失活突变。免疫组织化学测定的特异性在同基因细胞系的异种移植肿瘤中得到证实，所述同基因细胞系由于工程基因敲除而在DPC 4遗传状态上不同。因此，DPC 4的核定位可以在具有失活的TGF-β II型受体的细胞中维持，这表明上游信号传导输入的肿瘤抑制作用的持续性，最有可能是与TGF-β不同的配体/受体复合物。预期相关输入的鉴定将对理解肿瘤发生和设计合理的生物治疗具有意义。
The tumor-suppressor protein Dpc4 (Smad4, Madh4) regulates gene expression. On binding of an extracellular ligand of the extensive transforming growth factor (TGF) superfamily to its cognate receptor complex, latent cytoplasmic Dpc4 is activated and translocated into the nucleus to function as part of various DNA-binding transcriptional activator complexes, The most relevant ligand/receptor pair to control the tumor suppressive function of Dpc4 remains uncertain, but is usually assumed to be TGF-P and its heteromeric receptor. We exploited a fortuitous experiment of nature to directly test this hypothesis: the TGF-P type II receptor gene is inactivated by mutation in nearly all colorectal carcinomas having microsatellite instability, as seen in hereditary nonpolyposis colorectal cancer (HNPCC) and in sporadic medullary colorectal cancers, Using a specific and sensitive immunohistochemical label for Dpc4, we examined nuclear localization of Dpc4 in 13 HNPCC, six medullary, and 41 sporadic nonmedullary colorectal carcinomas. In agreement with published rates, two (5%) of 41 sporadic tumors showed complete loss of Dpc4 protein, indicative of genetic inactivation. All 13 HNPCC and six medullary tumors had intact cytoplasmic and nuclear Dpc4 localization. The TGFBR2 gene was sequenced in three of the cancers from patients with HNPCC, and all of these harbored inactivating mutations, The specificity of the immunohistochemical assay was demonstrated in xenograft tumors of syngeneic cell lines that differed in DPC4 genetic status because of an engineered gene knockout. Thus, nuclear localization of Dpc4 can be maintained in cells with inactivated TGF-P type II receptors, suggesting the persistence of tumor-suppressive action of an upstream signaling input, most likely a ligand/receptor complex distinct from TGF-P, Identification of the relevant input would be expected to have implications for the understanding of tumorigenesis and the design of rational biological therapy.