Stromal fibroblasts facilitate cancer cell invasion by a novel invadopodia-independent matrix degradation process.

Metastatic invasion of tumors into peripheral tissues is known to rely upon protease-mediated degradation of the surrounding stroma. This remodeling process uses complex, actin-based, specializations of the plasma membrane termed invadopodia that act both to sequester and release matrix metalloproteinases. Here we report that cells of mesenchymal origin, including tumor-associated fibroblasts, degrade substantial amounts of surrounding matrix by a mechanism independent of conventional invadopodia.

Chapter 1: roles of caldesmon in cell motility and actin cytoskeleton remodeling.

Caldesmon (CaD) is a multimodular protein that regulates contractility and actin cytoskeleton remodeling in smooth muscle and nonmuscle cells. A single gene (CALD1) encodes high molecular mass CaD (h-CaD) and low molecular mass CaD (l-CaD) by alternative splicings. The h-CaD exclusively expresses in smooth muscle, whereas the l-CaD ubiquitously expresses in all cell types except skeletal muscle.

Human tropomyosin isoforms in the regulation of cytoskeleton functions.

Over the past two decades, extensive molecular studies have identified multiple tropomyosin isoforms existing in all mammalian cells and tissues. In humans, tropomyosins are encoded by TPM1 (alpha-Tm, 15q22.1), TPM2 (beta-Tm, 9p13.

Opposite effects of overexpressed myosin Va or heavy meromyosin Va on vesicle distribution, cytoskeleton organization, and cell motility in nonmuscle cells.

Myosin Va, an actin-based motor protein that transports intracellular cargos, can bundle actin in vitro. Whether myosin Va regulates cellular actin dynamics or cell migration remains unclear. To address this, we compared Chinese Hamster Ovary (CHO) cells that stably express GFP fused to either full length mouse myosin Va (GFP-M5) or heavy meromyosin Va (GFP-M5Delta).

Tropomyosin and caldesmon regulate cytokinesis speed and membrane stability during cell division.

The contractile ring and the cell cortex generate force to divide the cell while maintaining symmetrical shape. This requires temporal and spatial regulation of the actin cytoskeleton at these areas. We force-expressed misregulated versions of actin-binding proteins, tropomyosin and caldesmon, into cells and analyzed their effects on cell division.

Requirement of reversible caldesmon phosphorylation at P21-activated kinase-responsive sites for lamellipodia extensions during cell migration.

Caldesmon is believed to be one of the key regulators for actin dynamics and thereby cell polarity, membrane extension, and cell motility. We have shown previously that stress fiber formation and cell movement are severely impaired in the cells expressing human fibroblast caldesmon fragment defective in Ca2+/CaM binding sites. Both Ser458 and Ser489, adjacent to the Ca2+/CaM-binding sites, are phosphorylated by p21-activated kinase (PAK) in vitro.