Nonmuscle myosin heavy chain IIA mediates integrin LFA-1 de-adhesion during T lymphocyte migration

Precise spatial and temporal regulation of cell adhesion and de-adhesion is critical for dynamic lymphocyte migration. Although a great deal of information has been learned about integrin lymphocyte function–associated antigen (LFA)-1 adhesion, the mechanism that regulates efficient LFA-1 de-adhesion from intercellular adhesion molecule (ICAM)-1 during T lymphocyte migration is unknown. Here, we show that nonmuscle myosin heavy chain IIA (MyH9) is recruited to LFA-1 at the uropod of migrating T lymphocytes, and inhibition of the association of MyH9 with LFA-1 results in extreme uropod elongation, defective tail detachment, and decreased lymphocyte migration on ICAM-1, without affecting LFA-1 activation by chemokine CXCL-12. This defect was reversed by a small molecule antagonist that inhibits both LFA-1 affinity and avidity regulation, but not by an antagonist that inhibits only affinity regulation. Total internal reflection fluorescence microscopy of the contact zone between migrating T lymphocytes and ICAM-1 substrate revealed that inactive LFA-1 is selectively localized to the posterior of polarized T lymphocytes, whereas active LFA-1 is localized to their anterior. Thus, during T lymphocyte migration, uropodal adhesion depends on LFA-1 avidity, where MyH9 serves as a key mechanical link between LFA-1 and the cytoskeleton that is critical for LFA-1 de-adhesion

Effect of IL-6 overexpression on the metastatic Potential of rat Hepatocellular Carcinoma cells

Abstract BACKGROUND: Previous studies demonstrated that excess IL-6 production correlated with the metastatic potential of rat hepatocellular carcinoma cells. In the work reported here a retroviral construct containing the gene for murine IL-6 was introduced into otherwise nonmetastatic tumor cells to directly determine the effect of IL-6 overexpression on tumor metastatic potential. METHODS: The clonal cell lines 1682.C.2.9.L0 (L0, poorly metastatic) and 1682.C.2.9.L10 (L10, highly metastatic) were selected from a parental hepatocellular carcinoma induced in ACI rats by feeding an ethionine-containing diet. Viral supernatant was used to infect the PA317 amphotropic cell line, and retrovirus produced from these cells infected the poorly metastatic L0 hepatocellular carcinoma cell line. Neomycin-resistant cells were selected in G418 and designated L0-IL-6. RESULTS: As determined by bioassay, L0 cells produce 10 +/- 1.2 U/mL IL-6 in culture, whereas L10 cells release 95 +/- 11 U/mL (P < 0.01, Student's t-test). Retroviral-mediated IL-6 gene transfer resulted in the production of 1266 +/- 48 U/mL IL-6 by L0-IL-6 cells under identical culture conditions. When an inoculum of 5 x 10(6) cells is injected subcutaneously, both L0 and L10 cell lines result in primary tumors with equivalent rates of growth; only L10 cells metastasize to the lung, however. A similar inoculation of L0-IL-6 cells produced local tumors in all 24 animals tested. Interestingly, 15 of 24 (62%) animals presented with metastatic nodules in the abdominal cavity, whereas no such tumors were found in animals receiving L10 cells. CONCLUSION: Overexpression of IL-6 increases metastatic potential of tumor cells, with preferential metastases to the abdominal cavity when compared with tumor cells elaborating endogenous IL-6

Describing Directional Cell Migration with a Characteristic Directionality Time

<div><p>Many cell types can bias their direction of locomotion by coupling to external cues. Characteristics such as how fast a cell migrates and the directedness of its migration path can be quantified to provide metrics that determine which biochemical and biomechanical factors affect directional cell migration, and by how much. To be useful, these metrics must be reproducible from one experimental setting to another. However, most are not reproducible because their numerical values depend on technical parameters like sampling interval and measurement error. To address the need for a reproducible metric, we analytically derive a metric called directionality time, the minimum observation time required to identify motion as directionally biased. We show that the corresponding fit function is applicable to a variety of ergodic, directionally biased motions. A motion is ergodic when the underlying dynamical properties such as speed or directional bias do not change over time. Measuring the directionality of nonergodic motion is less straightforward but we also show how this class of motion can be analyzed. Simulations are used to show the robustness of directionality time measurements and its decoupling from measurement errors. As a practical example, we demonstrate the measurement of directionality time, step-by-step, on noisy, nonergodic trajectories of chemotactic neutrophils. Because of its inherent generality, directionality time ought to be useful for characterizing a broad range of motions including intracellular transport, cell motility, and animal migration.</p></div