Hic-5 remodeling of the stromal matrix promotes breast tumor progression

The remodeling of the stromal extracellular matrix (ECM) has a crucial, but incompletely understood role during tumor progression and metastasis. Hic-5, a focal adhesion scaffold protein, has previously been implicated in tumor cell invasion, proliferation and metastasis. To investigate the role of Hic-5 in breast tumor progression in vivo, Hic-5^-/- mice were generated and crossed with the Mouse Mammary Tumor Virus-Polyoma Middle T-Antigen mouse. Tumors from the Hic-5^-/-;PyMT mice exhibited increased latency and reduced growth, with fewer lung metastases, as compared with Hic-5^+/-;PyMT mice. Immunohistochemical analysis showed that Hic-5 is primarily expressed in the cancer-associated fibroblasts (CAFs). Further analysis revealed that the Hic-5^-/-;PyMT tumor stroma contains fewer CAFs and exhibits reduced ECM deposition. The remodeling of the stromal matrix by CAFs has been shown to increase tumor rigidity to indirectly regulate FAK Y397 phosphorylation in tumor cells to promote their growth and invasion. Accordingly, the Hic-5^-/-;PyMT tumor cells exhibited a reduction in FAK Y397 phosphorylation. Isolated Hic-5^-/-;PyMT CAFs were defective in stress fiber organization and exhibited reduced contractility. These cells also failed to efficiently deposit and organize the ECM in two and three dimensions. This, in turn, impacted three-dimensional MDA-MB-231 tumor cell migration behavior. Thus, using a new knockout mouse model, we have identified Hic-5 expression in CAFs as a key requirement for deposition and remodeling of the stromal ECM to promote non-cell autonomous breast tumor progression.