MTDH-SND1 interaction is crucial for expansion and activity of tumor-initiating cells in diverse oncogene- and carcinogen-induced mammary tumors.

The Metadherin gene (MTDH) is prevalently amplified in breast cancer and associated with poor prognosis; however, its functional contribution to tumorigenesis is poorly understood. Using mouse models representing different subtypes of breast cancer, we demonstrated that MTDH plays a critical role in mammary tumorigenesis by regulating oncogene-induced expansion and activities of tumor-initiating cells (TICs), whereas it is largely dispensable for normal development. Mechanistically, MTDH supports the survival of mammary epithelial cells under oncogenic/stress conditions by interacting with and stabilizing Staphylococcal nuclease domain-containing 1 (SND1). Silencing MTDH or SND1 individually or disrupting their interaction compromises tumorigenenic potential of TICs in vivo. This functional significance of MTDH-SND1 interaction is further supported by clinical analysis of human breast cancer samples.

VCAM-1 promotes osteolytic expansion of indolent bone micrometastasis of breast cancer by engaging α4ß1-positive osteoclast progenitors.

Breast cancer patients often develop locoregional or distant recurrence years after mastectomy. Understanding the mechanism of metastatic recurrence after dormancy is crucial for improving the cure rate for breast cancer. Here, we characterize a bone metastasis dormancy model to show that aberrant expression of vascular cell adhesion molecule 1 (VCAM-1), in part dependent on the activity of the NF-κB pathway, promotes the transition from indolent micrometastasis to overt metastasis. By interacting with the cognate receptor integrin α4ß1, VCAM-1 recruits monocytic osteoclast progenitors and elevates local osteoclast activity. Antibodies against VCAM-1 and integrin α4 effectively inhibit bone metastasis progression and preserve bone structure. These findings establish VCAM-1 as a promising target for the prevention and inhibition of metastatic recurrence in bone.

Direct targeting of Sec23a by miR-200s influences cancer cell secretome and promotes metastatic colonization.

Although the role of miR-200s in regulating E-cadherin expression and epithelial-to-mesenchymal transition is well established, their influence on metastatic colonization remains controversial. Here we have used clinical and experimental models of breast cancer metastasis to discover a pro-metastatic role of miR-200s that goes beyond their regulation of E-cadherin and epithelial phenotype. Overexpression of miR-200s is associated with increased risk of metastasis in breast cancer and promotes metastatic colonization in mouse models, phenotypes that cannot be recapitulated by E-cadherin expression alone. Genomic and proteomic analyses revealed global shifts in gene expression upon miR-200 overexpression toward that of highly metastatic cells. miR-200s promote metastatic colonization partly through direct targeting of Sec23a, which mediates secretion of metastasis-suppressive proteins, including Igfbp4 and Tinagl1, as validated by functional and clinical correlation studies. Overall, these findings suggest a pleiotropic role of miR-200s in promoting metastatic colonization by influencing E-cadherin-dependent epithelial traits and Sec23a-mediated tumor cell secretome.

Identification of staphylococcal nuclease domain-containing 1 (SND1) as a Metadherin-interacting protein with metastasis-promoting functions.

Metastasis is the deadliest and most poorly understood feature of malignant diseases. Recent work has shown that Metadherin (MTDH) is overexpressed in over 40% of breast cancer patients and promotes metastasis and chemoresistance in experimental models of breast cancer progression. Here we applied mass spectrometry-based screen to identify staphylococcal nuclease domain-containing 1 (SND1) as a candidate MTDH-interacting protein. After confirming the interaction between SND1 and MTDH, we tested the role of SND1 in breast cancer and found that it strongly promotes lung metastasis. SND1 was further shown to promote resistance to apoptosis and to regulate the expression of genes associated with metastasis and chemoresistance. Analyses of breast cancer clinical microarray data indicated that high expression of SND1 in primary tumors is strongly associated with reduced metastasis-free survival in multiple large scale data sets. Thus, we have uncovered SND1 as a novel MTDH-interacting protein and shown that it is a functionally and clinically significant mediator of metastasis.