State Key Laboratory of Oncogenes and Related Genes, Renji-MedX Stem Cell Research Center, Ren Ji Hospital, School of Medicine, Shanghai Jiao Tong University, 160 Pujian Road, Shanghai, 200127, China.
Department of Breast Surgery, Ren Ji Hospital, School of Medicine, Shanghai Jiao Tong University, 160 Pujian Road, Shanghai, 200127, China.
J Exp Clin Cancer Res. 2019 Jan 21;38(1):27. doi: 10.1186/s13046-019-1025-2.
Breast cancer (BCa) remains as the second leading cause of cancer-related death in women worldwide. The majority of the deaths are due to its progression to metastatic BCa. Although Grb2-associated binding protein 1 (Gab1) has been implicated in tumor proliferation and metastasis in multiple tumors including colorectal cancer, hepatocellular carcinoma and ovarian cancer, whether and how it regulates BCa metastasis are still poorly understood.
Western blot assay and immunohistochemical (IHC) staining were performed to assess expression of Gab1 in primary and metastatic BCa clinical samples. Biological function assay studies in vitro and in vivo were employed to investigate the functions of Gab1 during BCa metastasis. Co-immunoprecipitation (co-IP) assessment, western blot assay and immunofluorescence (IF) staining were carried out to investigate the underlying mechanism for the function of Gab1 on BCa metastasis.
In this study, we found that expression level of Gab1 was increased significantly in BCa tissue samples compared to that in benign mammary hyperplastic tissues. Furthermore, elevated expression of Gab1 was positively associated with metastasis in HER2 and TNBC subtypes of BCa. In BCa cell line MDA-MB-231 and SK-BR3 cells, stable overexpression of Gab1 promoted, while knockdown of Gab1 inhibited cell migration in vitro and metastasis in vivo. Mechanistically, overexpression of Gab1 enhanced its interaction with Par3, a key component of the polarity-associated partitioning defective (PAR) complex, leading to a dissociation of the PAR complex. Consequently, dissociated PAR complex induced epithelial-to-mesenchymal transition (EMT) for breast tumor metastasis. By restoration assessment, we found that only re-expression of a fully functional Gab1, but not a mutant Gab1 that harbors either Par3 binding-deficiency or Par1b binding-deficiency, could reverse the repressive phenotype of cell migration in vitro and metastasis in vivo due to Gab1 knockdown.
Our findings indicate that elevated expression of Gab1 promotes BCa metastasis by dissociating the PAR complex that leads to EMT, implicating a role of Gab1 as a potential biomarker of metastatic BCa. Moreover, inhibition of Gab1 expression might be a promising therapeutic strategy for BCa metastasis.
乳腺癌（BCa）仍然是全球女性癌症相关死亡的第二大主要原因。大多数死亡是由于其进展为转移性 BCa。虽然 Grb2 相关结合蛋白 1（Gab1）已被牵连到多种肿瘤包括结直肠癌、肝细胞癌和卵巢癌的肿瘤增殖和转移中，但它如何调节 BCa 转移仍知之甚少。
通过 Western blot 检测和免疫组织化学（IHC）染色评估 Gab1 在原发性和转移性 BCa 临床样本中的表达。体外和体内的生物学功能研究用于研究 Gab1 在 BCa 转移过程中的功能。通过共免疫沉淀（co-IP）评估、Western blot 检测和免疫荧光（IF）染色研究 Gab1 对 BCa 转移功能的潜在机制。
在这项研究中，我们发现 Gab1 的表达水平在 BCa 组织样本中与良性乳腺增生组织相比显著增加。此外，Gab1 的高表达与 BCa 中 HER2 和 TNBC 亚型的转移呈正相关。在 BCa 细胞系 MDA-MB-231 和 SK-BR3 细胞中，Gab1 的稳定过表达促进了细胞迁移，而 Gab1 的敲低抑制了体外迁移和体内转移。机制上，Gab1 的过表达增强了其与 Par3 的相互作用，Par3 是极性相关的分区缺陷（PAR）复合物的关键组成部分，导致 PAR 复合物的解离。因此，分离的 PAR 复合物诱导了乳腺癌转移的上皮-间充质转化（EMT）。通过恢复评估，我们发现只有完全功能的 Gab1 的重新表达，而不是具有 Par3 结合缺陷或 Par1b 结合缺陷的突变 Gab1，才能逆转由于 Gab1 敲低导致的体外细胞迁移和体内转移的抑制表型。
我们的研究结果表明，Gab1 的高表达通过解离导致 EMT 的 PAR 复合物促进 BCa 转移，表明 Gab1 作为转移性 BCa 的潜在生物标志物的作用。此外，抑制 Gab1 表达可能是 BCa 转移的一种有前途的治疗策略。
