Divergent iron regulatory states contribute to heterogeneity in breast cancer aggressiveness.

Contact with dense collagen I (Col1) can induce collective invasion of triple negative breast cancer (TNBC) cells and transcriptional signatures linked to poor patient prognosis. However, this response is heterogeneous and not well understood. Using phenotype-guided sequencing analysis of invasive vs. noninvasive subpopulations, we show that these two phenotypes represent opposite sides of the iron response protein 1 (IRP1)-mediated response to cytoplasmic labile iron pool (cLIP) levels. Invasive cells upregulate iron uptake and utilization machinery characteristic of a low cLIP response, which includes contractility regulating genes that drive migration. Non-invasive cells upregulate iron sequestration machinery characteristic of a high cLIP response, which is accompanied by upregulation of actin sequestration genes. These divergent IRP1 responses result from Col1-induced transient expression of heme oxygenase I (HO-1), which cleaves heme and releases iron. These findings lend insight into the emerging theory that heme and iron fluxes regulate TNBC aggressiveness.

3D collagen architecture regulates cell adhesion through degradability, thereby controlling metabolic and oxidative stress.

The collagen-rich tumor microenvironment plays a critical role in directing the migration behavior of cancer cells. 3D collagen architectures with small pores have been shown to confine cells and induce aggressive collective migration, irrespective of matrix stiffness and density. However, it remains unclear how cells sense collagen architecture and transduce this information to initiate collective migration. Here, we tune collagen architecture and analyze its effect on four core cell-ECM interactions: cytoskeletal polymerization, adhesion, contractility, and matrix degradation. From this comprehensive analysis, we deduce that matrix architecture initially modulates cancer cell adhesion strength, and that this results from architecture-induced changes to matrix degradability. That is, architectures with smaller pores are less degradable, and degradability is required for cancer cell adhesion to 3D fibrilar collagen. The biochemical consequences of this 3D low-attachment state are similar to those induced by suspension culture, including metabolic and oxidative stress. One distinction from suspension culture is the induction of collagen catabolism that occurs in 3D low-attachment conditions. Cells also upregulate Snail1 and Notch signaling in response to 3D low-attachment, which suggests a mechanism for the emergence of collective behaviors.