Abstract
BackgroundAs the first member of the metastasis-associated protein (MTA) family, MTA1 and another MTA family member, MTA2, have both been reported to promote breast cancer progression and metastasis. However, the difference and relationship between MTA1 and MTA2 have not been fully elucidated.MethodsTranswell assays were used to assess the roles of MTA1 and MTA2 in the metastasis of ZR-75-30 luminal B breast cancer cells in vitro. Immunoblotting and qRT-PCR were used to evaluate the effect of MTA1 overexpression on MTA2. Proteases that cleave MTA2 were predicted using an online web server. The role of neutrophil elastase (NE) in MTA1 overexpression-induced MTA2 downregulation was confirmed by specific inhibitor treatment, knockdown, overexpression and immunocytochemistry, and NE cleavage sites in MTA2 were confirmed by MTA2 truncation and mutation. The effect of MTA1 overexpression on the intrinsic inhibitor of NE, elafin, was detected by qRT-PCR, immunoblotting and treatment with inhibitors.ResultsMTA1 overexpression inhibited, while MTA2 promoted the metastasis of ZR-75-30 cells in vitro. MTA1 overexpression downregulated MTA2 expression at the protein level rather than the mRNA level. NE was predicted to cleave MTA2 and was responsible for MTA1 overexpression-induced MTA2 degradation. NE was found to cleave MTA2 in the C-terminus at the 486, 497, 542, 583 and 621 sites. MTA1 overexpression activated NE by downregulating elafin in a histone deacetylase- and DNA methyltransferase-dependent manner.ConclusionsMTA1 and MTA2 play opposing roles in the metastasis of ZR-75-30 luminal B breast cancer cells in vitro. MTA1 downregulates MTA2 at the protein level by epigenetically repressing the expression of elafin and releasing the inhibition of neutrophil elastase, which cleaves MTA2 in the C-terminus at multiple specific sites.
Highlights
As the first member of the metastasis-associated protein (MTA) family, MTA1 and another MTA family member, MTA2, have both been reported to promote breast cancer progression and metastasis
We investigated the roles of MTA1 and MTA2 in the metastasis of the ZR-75-30 luminal B breast cancer cell line [20, 21], and we found that the overexpression of MTA1 inhibits the metastasis of ZR-75-30 cells by downregulating MTA2, which has not been clarified previously [19]
MTA1 overexpression inhibited the metastasis of ZR-7530 luminal B breast cancer cells in vitro To investigate the role of MTA1 in luminal B breast cancer metastasis, we first established two stable cell lines, ZR-75-30-MTA1 overexpressing MTA1 and ZR75-30-Vector as a control
Summary
As the first member of the metastasis-associated protein (MTA) family, MTA1 and another MTA family member, MTA2, have both been reported to promote breast cancer progression and metastasis. To overcome the problem of breast cancer metastasis, a 13762NF rat mammary adenocarcinoma metastasis model was established, and the first member of the metastasis associated protein (MTA) family, MTA1, was discovered by differential cDNA library screening in 1994 [7]. MTA1 and MTA2 have both been reported to be pivotal for epithelial-mesenchymal transition (EMT) and metastasis of breast cancer, while MTA3 has been reported to inhibit EMT [12, 14,15,16]. EMT is a critical step among a sequence of discrete steps that cancer cells undergo to achieve metastasis [17, 18]. During EMT, the EMT-inducing factors Snail, Slug, TWIST and ZEB1 are upregulated, the epithelial molecule E-cadherin is downregulated and the mesenchymal molecule N-cadherin is upregulated [17, 18]
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