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The remodeling of the stromal extracellular matrix (ECM) plays 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 (MMTV-PyMT) mouse. Tumors from the Hic-5−/−;PyMT mice exhibited increased latency and reduced growth, with fewer lung metastases, as compared to 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.

TLR-mediated recognition of microbial danger induces substantial changes in macrophage migration, adherence, and phagocytosis. Recently, we described the LPS-regulated phosphorylation of many cytoskeleton-associated proteins by phosphoproteomics. The functional role of these cytoskeletal and motor proteins in innate immune cell responses is largely unexplored. Here, we first identified both long-tailed class I myosins Myo1e and Myo1f as important contributors to LPS-triggered macrophage spreading. Mouse bone marrow-derived macrophages and DCs deficient in Myo1e selectively secreted increased amounts of the chemokine CCL2. In addition, the cell surface expression of MHC class II (MHC-II) on both cell types was reduced in the absence of Myo1e. However, transcriptional changes in CCL2 and MHC-II were not observed in the absence of Myo1e, indicating that Myo1e regulates specific intracellular transport processes. The capacity of macrophages and DCs lacking Myo1e to stimulate antigen-specific CD4(+) T-cell proliferation was impaired, consistent with the reduced MHC-II surface protein levels. Surprisingly, in Myo1e-deficient DCs, the proteolytic cleavage of endocytosed antigen was also increased. Together, our results provide evidence for a non-redundant function of the motor protein Myo1e in the regulation of TLR4-controlled, cytoskeleton-associated functional properties of macrophages and DCs, and in induction of a full MHC-II-restricted adaptive immune response.

The actin cytoskeleton, which regulates cell polarity, adhesion, and migration, can influence cancer progression, including initial acquisition of malignant properties by normal cells, invasion of adjacent tissues, and metastasis to distant sites. Actin-dependent molecular motors, myosins, play key roles in regulating tumor progression and metastasis. In this review, we examine how non-muscle myosins regulate neoplastic transformation and cancer cell migration and invasion. Members of the myosin superfamily can act as either enhancers or suppressors of tumor progression. This review summarizes the current state of knowledge on how mutations or epigenetic changes in myosin genes and changes in myosin expression may affect tumor progression and patient outcomes and discusses the proposed mechanisms linking myosin inactivation or upregulation to malignant phenotype, cancer cell migration, and metastasis.

Myosin 1e (myo1e) is an actin-based motor protein that has been implicated in cell adhesion and migration. We examined the role of myo1e in invadosomes, actin-rich adhesion structures that are important for degradation and invasion of the extracellular matrix. RSV-transformed BHK-21 cells, which readily form invadosomes and invadosome rosettes, were used as the experimental model. Myo1e localization to the actin-rich core of invadosomes required the proline-rich Tail Homology 2 (TH2) domain. During invadosome rosette expansion, we observed myo1e recruitment to newly forming invadosomes via Tail Homology 1 (TH1)-dependent interactions with the plasma membrane, where it preceded actin and paxillin. Dominant-negative inhibition of myo1e resulted in mislocalized invadosome formation, usually at the center of the rosette. We propose that TH2 domain of myo1e provides the key signal for localization to invadosomes, while TH1 domain interactions facilitate myo1e targeting to the plasma membrane-proximal locations within the rosettes. Myo1e may then act as a scaffold, linking the plasma membrane with the actin cytoskeleton and helping direct new invadosome formation to the periphery of the rosette.

Formins are actin-binding proteins conserved across species from plants to humans. The formin family is defined by their common formin homology (FH2) domains. The 15 distinct human formins are involved in a broad range of cellular functions, including cell adhesion, cytokinesis, cell polarity, and cell morphogenesis. Their commonality is actin polymerization activity inherent to FH2 domains. Although still requiring much study, biochemical activity of formins has been carefully described. In contrast, much less is known of their activities in complex living systems. With the diversity of the formin family and the actin structures that they affect, an extensive future of study beckons. In this study, we report the expression level of all 15 formins in 22 different human cell and tissue types using quantitative real-time PCR. Identification of major themes in formin expression and documentation of expression profiles should facilitate the cellular study of formins. © 2013 Wiley Periodicals, Inc.

Point mutations in the human MYO1E gene, encoding class I myosin Myo1e, are associated with focal segmental glomerulosclerosis (FSGS), a primary kidney disorder that leads to end-stage kidney disease. In this study, we used a simple model organism, fission yeast Schizosaccharomyces pombe, to test the effects of FSGS-associated mutations on myosin activity. Fission yeast has only one class I myosin, Myo1, which is involved in actin patch assembly at the sites of endocytosis. The amino acid residues mutated in individuals with FSGS are conserved between human Myo1e and yeast Myo1, which allowed us to introduce equivalent mutations into yeast myosin and use the resulting mutant strains for functional analysis. Yeast strains expressing mutant Myo1 exhibited defects in growth and endocytosis similar to those observed in the myo1 deletion strain. These mutations also disrupted Myo1 localization to endocytic actin patches and resulted in mis-localization of Myo1 to eisosomes, linear membrane microdomains found in yeast cells. Although both mutants examined in this study exhibited loss of function, one of these mutants was also characterized by the decreased protein stability. Thus, using the yeast model system, we were able to determine that the kidney-disease-associated mutations impair myosin functional activity and have differential effects on protein stability., Summary: In the fission yeast S. pombe, kidney disease-associated mutations in Myo1, a homolog of human Myo1e, disrupt myosin localization and function.

Primary tumors grow and invade into surrounding tissues/stroma, frequently resulting in metastasis to distant organs. Tumor cell-stroma crosstalk plays a crucial, but incompletely understood role during tumor progression and metastasis. For example, increased stromal matrix density and/or rigidity correlates with poor prognosis in human breast cancer patients. Previous studies have implicated Hic-5, a focal adhesion scaffold protein, in tumor cell invasion, proliferation and metastasis. To investigate the role of Hic-5 in mammary tumor progression, Hic-5 -/- mice were generated and crossed with mice expressing Polyoma Middle T Antigen (PyMT) driven by the MMTV promoter. The PyMT mouse is a well-established model for human breast cancer progression. Tumors from the Hic-5 -/- PyMT mice demonstrated an increased latency and had reduced growth as compared to Hic-5 +/- PyMT controls. The absence of Hic-5 did not affect the progression of the tumor to a carcinoma stage, but there was a decrease in metastasis to the lungs. Immunohistochemical analysis showed that Hic-5 is primarily expressed in the cancer associated fibroblasts (CAFs) and the Hic-5 -/- PyMT tumor stroma exhibits reduced extracellular matrix (ECM) deposition. Furthermore, 3D cell-derived matrices (CDM) generated in vitro using isolated CAFs, confirmed that Hic-5 -/- PyMT CAFs do not efficiently deposit and organize ECM. The organization of the stromal matrix has been shown previously to increase the rigidity of the tumor, which in turn promotes FAK Y397 phosphorylation in the tumor cells to promote cell invasion and proliferation. Accordingly, the Hic-5 -/- PyMT tumors exhibited a reduction in FAK phospho-Y397 staining and attenuation of downstream ERK activation, suggesting that their stromal matrix is not optimally organized for tumor cell signaling. Taken together, these data demonstrate that Hic-5 expression in CAFs is important for stromal matrix organization/remodeling during tumor progression and that the loss of the organization of the ECM in the Hic-5 -/- tumor stroma may contribute to the reduced tumor growth and metastasis observed in these animals. Supported by NIH CA163296 to CET, NS066071 to EO and Carol M. Baldwin Breast Cancer Fund to CET. Citation Format: Gregory J. Goreczny, Jessica Ouderkirk, Eric Olson, Mira Krendel, Christopher Turner. Hic-5 modulation of the stromal matrix is required for mammary tumor progression. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5095.