Crossing boundaries of light microscopy resolution discerns novel assemblies in the nucleolus.

The nucleolus is the largest membraneless organelle and nuclear body in mammalian cells. It is primarily involved in the biogenesis of ribosomes, essential macromolecular machines responsible for synthesizing all proteins required by the cell. The assembly of ribosomes is evolutionarily conserved and accounts for the most energy-consuming cellular process needed for cell growth, proliferation, and homeostasis.

Physical confinement alters tumor cell adhesion and migration phenotypes.

Cell migration on planar surfaces is driven by cycles of actin protrusion, integrin-mediated adhesion, and myosin-mediated contraction; however, this mechanism may not accurately describe movement in 3-dimensional (3D) space. By subjecting cells to restrictive 3D environments, we demonstrate that physical confinement constitutes a biophysical stimulus that alters cell morphology and suppresses mesenchymal motility in human breast carcinoma (MDA-MB-231). Dorsoventral polarity, stress fibers, and focal adhesions are markedly attenuated by confinement.

Loss of giant obscurins promotes breast epithelial cell survival through apoptotic resistance.

Obscurins (∼70 - 870 kDa), encoded by the single OBSCN gene, are cytoskeletal proteins originally identified in striated muscles with structural and regulatory roles. Recently, analysis of 13,023 genes in breast and colorectal cancers identified OBSCN as one of the most frequently mutated genes, implicating it in cancer formation. Herein we studied the expression profile of obscurins in breast, colon, and skin cancer cell lines and their involvement in cell survival.

Chemotaxis of cell populations through confined spaces at single-cell resolution.

Cell migration is crucial for both physiological and pathological processes. Current in vitro cell motility assays suffer from various drawbacks, including insufficient temporal and/or optical resolution, or the failure to include a controlled chemotactic stimulus. Here, we address these limitations with a migration chamber that utilizes a self-sustaining chemotactic gradient to induce locomotion through confined environments that emulate physiological settings.

Mucin 16 is a functional selectin ligand on pancreatic cancer cells.

Selectins promote metastasis by mediating specific interactions between selectin ligands on tumor cells and selectin-expressing host cells in the microvasculature. Using affinity chromatography in conjunction with tandem mass spectrometry and bioinformatics tools, we identified mucin 16 (MUC16) as a novel selectin ligand expressed by metastatic pancreatic cancer cells. While up-regulated in many pancreatic cancers, the biological function of sialofucosylated MUC16 has yet to be fully elucidated.

Intercellular adhesion: mechanisms for growth and metastasis of epithelial cancers.

Cell-cell adhesion molecules (CAMs) comprise a broad class of linker proteins that are crucial for the development of multicellular organisms, and for the continued maintenance of organ and tissue structure. Because of its pivotal function in tissue homeostasis, the deregulation of intercellular adhesion is linked to the onset of most solid tumors. The breakdown of homeostatic cell adhesions in highly ordered epithelial sheets is directly implicated in carcinogenesis, while continued changes in the adhesion profile of the primary tumor mass facilitate growth and expansion into adjacent tissue.

Biophysics of selectin-ligand interactions in inflammation and cancer.

Selectins (L-, E- and P-selectin) are calcium-dependent transmembrane glycoproteins that are expressed on the surface of circulating leukocytes, activated platelets, and inflamed endothelial cells. Selectins bind predominantly to sialofucosylated glycoproteins and glycolipids (E-selectin only) present on the surface of apposing cells, and mediate transient adhesive interactions pertinent to inflammation and cancer metastasis. The rapid turnover of selectin-ligand bonds, due to their fast on- and off-rates along with their remarkably high tensile strengths, enables them to mediate cell tethering and rolling in shear flow.

Local anesthetics inhibit kinesin motility and microtentacle protrusions in human epithelial and breast tumor cells.

Detached breast tumor cells produce dynamic microtubule protrusions that promote reattachment of cells and are termed tubulin microtentacles (McTNs) due to their mechanistic distinctions from actin-based filopodia/invadopodia and tubulin-based cilia. McTNs are enriched with vimentin and detyrosinated α-tubulin, (Glu-tubulin). Evidence suggests that vimentin and Glu-tubulin are cross-linked by kinesin motor proteins.

Microtentacles tip the balance of cytoskeletal forces in circulating tumor cells.

Detection of circulating tumor cells (CTC) is advancing as an effective predictor of patient outcome and therapeutic response. Unfortunately, our knowledge of CTC biology remains limited, and the impact of drug treatments on CTC metastatic potential is currently unclear. Improved CTC imaging in vivo and analysis of free-floating tumor cells now show that cytoskeletal regulation in CTCs contrasts starkly with tumor cells attached to extracellular matrix.

Epithelial-to-mesenchymal transition promotes tubulin detyrosination and microtentacles that enhance endothelial engagement.

Epithelial-to-mesenchymal transition (EMT) is associated with increased breast tumor metastasis; however, the specific mechanisms by which EMT promotes metastasis remain somewhat unclear. Despite the importance of cytoskeletal dynamics during both EMT and metastasis, very few current studies examine the cytoskeleton of detached and circulating tumor cells. Specific posttranslational α-tubulin modifications are critical for adherent cell motility and implicated in numerous pathologies, but also remain understudied in detached cells.

Delocalization of gamma-tubulin due to increased solubility in human breast cancer cell lines.

The centrosome is the major organelle responsible for the nucleation and organization of microtubules into arrays. Recent studies demonstrate that microtubules can nucleate outside the centrosome. The molecular mechanisms controlling acentrosomal microtubule nucleation are currently poorly defined, and the function of this type of microtubule regulation in tumor cell biology is particularly unclear.

Antimitotic chemotherapeutics promote adhesive responses in detached and circulating tumor cells.

In the clinical treatment of breast cancer, antimitotic cytotoxic agents are one of the most commonly employed chemotherapies, owing largely to their antiproliferative effects on the growth and survival of adherent cells in studies that model primary tumor growth. Importantly, the manner in which these chemotherapeutics impact the metastatic process remains unclear. Furthermore, since dissemination of tumor cells through the systemic circulation and lymphatics necessitates periods of detached survival, it is equally important to consider how circulating tumor cells respond to such compounds.

Vimentin filaments support extension of tubulin-based microtentacles in detached breast tumor cells.

Solid tumor metastasis often involves detachment of epithelial carcinoma cells into the vasculature or lymphatics. However, most studies of cytoskeletal rearrangement in solid tumors focus on attached cells. In this study, we report for the first time that human breast tumor cells produce unique tubulin-based protrusions when detached from extracellular matrix.