RNA-binding proteins play diverse roles in cancer, influencing various facets of the disease, including proliferation, apoptosis, angiogenesis, senescence, invasion, epithelial–mesenchymal transition (EMT), and metastasis. HuR, a known RBP, is recognized for stabilizing mRNAs containing AU-rich elements (AREs), although its complete repertoire of mRNA targets remains undefined. Through a bioinformatics analysis of the gene expression profile of the Hs578T basal-like triple-negative breast cancer cell line with silenced HuR, we have identified SOX9 as a potential HuR-regulated target. SOX9 is a transcription factor involved in promoting EMT, metastasis, survival, and the maintenance of cancer stem cells (CSCs) in triple-negative breast cancer. Ribonucleoprotein immunoprecipitation assays confirm a direct interaction between HuR and SOX9 mRNA. The half-life of SOX9 mRNA and the levels of SOX9 protein decreased in cells lacking HuR. Cells silenced for HuR exhibit reduced migration and invasion compared to control cells, a phenotype similar to that described for SOX9-silenced cells.

Epithelial-to-mesenchymal transition (EMT) triggers cell plasticity in embryonic development, adult injured tissues and cancer. Combining the analysis of EMT in cell lines, embryonic neural crest and mouse models of renal fibrosis and breast cancer, we find that there is not a cancer-specific EMT program. Instead, cancer cells dedifferentiate and bifurcate into two distinct and segregated cellular trajectories after activating either embryonic-like or adult-like EMTs to drive dissemination or inflammation, respectively. We show that SNAIL1 acts as a pioneer factor in both EMT trajectories, and PRRX1 drives the progression of the embryonic-like invasive trajectory. We also find that the two trajectories are plastic and interdependent, as the abrogation of the EMT invasive trajectory by deleting Prrx1 not only prevents metastasis but also enhances inflammation, increasing the recruitment of antitumor macrophages. Our data unveil an additional role for EMT in orchestrating intratumor heterogeneity, driving the distribution of functions associated with either inflammation or metastatic dissemination. Youssef et al. study epithelial-to-mesenchymal transition (EMT) programs in breast cancer and identify two interdependent trajectories coexisting within tumors, with EMT transcription factors such as PRRX1 at their nexus.

Lysyl oxidase-like 2 (LOXL2) was initially described as an extracellular enzyme involved in extracellular matrix remodeling. Nevertheless, numerous recent reports have implicated intracellular LOXL2 in a wide variety of processes that impact on gene transcription, development, differentiation, proliferation, migration, cell adhesion, and angiogenesis, suggesting multiple different functions for this protein. In addition, increasing knowledge about LOXL2 points to a role in several types of human cancer. Moreover, LOXL2 is able to induce the epithelial-to-mesenchymal transition (EMT) process-the first step in the metastatic cascade. To uncover the underlying mechanisms of the great variety of functions of intracellular LOXL2, we carried out an analysis of LOXL2's nuclear interactome. This study reveals the interaction of LOXL2 with numerous RNA-binding proteins (RBPs) involved in several aspects of RNA metabolism. Gene expression profile analysis of cells silenced for LOXL2, combined with in silico identification of RBPs' targets, points to six RBPs as candidates to be substrates of LOXL2's action, and that deserve a more mechanistic analysis in the future. The results presented here allow us to hypothesize novel LOXL2 functions that might help to comprehend its multifaceted role in the tumorigenic process.

Collagen organization in metastatic lungs (Fig. S6) and Tenascin-C and fibronectin expression in primary tumors and lungs from PyMT mice with deregulated Loxl2

Supplementary Figure 5 from SNAI1 Is Required for Tumor Growth and Lymph Node Metastasis of Human Breast Carcinoma MDA-MB-231 Cells

Supplementary Figure 1 from SNAI1 Is Required for Tumor Growth and Lymph Node Metastasis of Human Breast Carcinoma MDA-MB-231 Cells

Supplementary Figures 1-4, Tables 1-2 from Genetic Profiling of Epithelial Cells Expressing E-Cadherin Repressors Reveals a Distinct Role for Snail, Slug, and E47 Factors in Epithelial-Mesenchymal Transition

E-cadherin expression in PyMT tumors with deleted (KO) and overexpressed Loxl2

Supplementary Methods and Supplementary Tables S1-S4

Supplementary Methods and Materials from SNAI1 Is Required for Tumor Growth and Lymph Node Metastasis of Human Breast Carcinoma MDA-MB-231 Cells

Supplementary Figure 1 from Lysyl Oxidase–Like 2 as a New Poor Prognosis Marker of Squamous Cell Carcinomas

Abstract The lysyl oxidase–like protein LOXL2 has been suggested to contribute to tumor progression and metastasis, but in vivo evidence has been lacking. Here we provide functional evidence that LOXL2 is a key driver of breast cancer metastasis in two conditional transgenic mouse models of PyMT-induced breast cancer. LOXL2 ablation in mammary tumor cells dramatically decreased lung metastasis, whereas LOXL2 overexpression promoted metastatic tumor growth. LOXL2 depletion or overexpression in tumor cells does not affect extracellular matrix stiffness or organization in primary and metastatic tumors, implying a function for LOXL2 independent of its conventional role in extracellular matrix remodeling. In support of this likelihood, cellular and molecular analyses revealed an association of LOXL2 action with elevated levels of the EMT regulatory transcription factor Snail1 and expression of several cytokines that promote premetastatic niche formation. Taken together, our findings established a pathophysiologic role and new function for LOXL2 in breast cancer metastasis. Cancer Res; 77(21); 5846–59. ©2017 AACR.

Size (Fig. S1) and expression of Lox family members in PyMT tumors (Fig. S2) with deregulated Loxl2. Fig. S3: Loxl2 expression in PyMT tumors compared to normal mammary gland.

Orthotopic injection of PyMT cells with Loxl2 overexpression (Fig. S8) and fibrillar collagen in xenografts from PyMT cells with deregulated Loxl2

Supplementary Tables 1-3 from Epithelial-Mesenchymal Transition in Breast Cancer Relates to the Basal-like Phenotype

Suppplementary Material and Methods and related references

Supplementary Tables from A Mouse Skin Multistage Carcinogenesis Model Reflects the Aberrant DNA Methylation Patterns of Human Tumors

CK14 expression in xenografts from PyMT cells overexpressing Loxl2

Supplementary Figure 4 from SNAI1 Is Required for Tumor Growth and Lymph Node Metastasis of Human Breast Carcinoma MDA-MB-231 Cells