Down-regulation of lactogenic hormone receptors in Nb2 lymphoma cells by cholera toxin

Exposure of lactogen-dependent (Nb2-11C) and lactogen independent (Nb2-SP) lymphoma cells to cholera toxin (0.05-50 pM) resulted within 18-28 h in a 50% decrease in the binding capacity of the intact cells to iodinated human growth hormone, and 40% decrease in cell-homogenates. Scatchard analysis revealed that the reduction in binding resulted from loss of cell-surface receptors accompanied by degradation of intracellular receptors. No alterations in receptor binding affinity were observed. One to 3 h of exposure to the toxin was sufficient to reduce the binding to the level obtained after continuous incubation with the toxin for 28 h. Addition of dibutyryl cAMP (0.1mM) to the medium resulted in similar down-regulation of lactogenic receptors.     

Effects of recombinant ovine interferon tau, placental lactogen, and growth hormone on the ovine uterus

Studies were conducted to determine effects of intrauterine administration of recombinant ovine interferon tau (IFNtau), placental lactogen (PL), and growth hormone (GH) on endometrial function. In the first study, administration of IFNtau to cyclic ewes for one period (Days 11-15) resulted in an interestrous interval (IEI) of approximately 30 days, whereas administration for two periods (Days 11-15 and Days 21-25) extended the IEI to greater than 50 days. Administration of IFNtau from Days 11 to 15 and of PL or GH from Days 21 to 25 failed to extend the IEI more than for IFNtau alone. In the second study, effects of IFNtau, PL, and GH on endometrial differentiation and function were determined in ovariectomized ewes receiving ovarian steroid replacement therapy. Endometrial expression of mRNAs for estrogen receptor (ER), progesterone receptor (PR), and oxytocin receptor (OTR) were not affected by PL or GH treatment; however, uterine milk protein mRNA levels and stratum spongiosum gland density were increased by both PL and GH treatments. Collectively, results indicated that 1) PL and GH do not regulate endometrial PR, ER, and OTR expression or affect corpus luteum life span; 2) down-regulation of epithelial PR expression is requisite for progesterone induction of secretory gene expression in uterine glandular epithelium; 3) effects of PL and GH on endometrial function require IFNtau; and 4) PL and GH regulate endometrial gland proliferation and perhaps differentiated function.     

Epidermal growth factor-induced enhancement of glioblastoma cell migration in 3D arises from an intrinsic increase in speed but an extrinsic matrix- and proteolysis-dependent increase in persistence

Epidermal growth factor (EGF) receptor-mediated cell migration plays a vital role in invasion of many tumor types. EGF receptor ligands increase invasiveness in vivo, but it remains unclear how consequent effects on intrinsic cell motility behavior versus effects on extrinsic matrix properties integrate to result in net increase of translational speed and/or directional persistence of migration in a 3D environment. Understanding this convolution is important for therapeutic targeting of tumor invasion, as key regulatory pathways for intrinsic versus extrinsic effects may not be coincident. Accordingly, we have undertaken a quantitative single-cell imaging study of glioblastoma cell movement in 3D matrices and on 2D substrata across a range of collagen densities with systematic variation of protease-mediated matrix degradation. In 3D, EGF induced a mild increase in cell speed and a strong increase in directional persistence, the latter depending heavily on matrix density and EGF-stimulated protease activity. In contrast, in 2D, EGF induced a similarly mild increase in speed but conversely a decrease in directional persistence (both independent of protease activity). Thus, the EGF-enhanced 3D tumor cell migration results only partially from cell-intrinsic effects, with override of cell-intrinsic persistence decrease by protease-mediated cell-extrinsic reduction of matrix steric hindrance.     

Feedback equilibrium control during human standing

Equilibrium maintenance during standing in humans was investigated with a 3-joint (ankle, knee and hip) sagittal model of body movement. The experimental paradigm consisted of sudden perturbations of humans in quiet stance by backward displacements of the support platform. Data analysis was performed using eigenvectors of motion equation. The results supported three conclusions. First, independent feedback control of movements along eigenvectors (eigenmovements) can adequately describe human postural responses to stance perturbations. This conclusion is consistent with previous observations (Alexandrov et al., 2001b) that these same eigenmovements are also independently controlled in a feed-forward manner during voluntary upper-trunk bending. Second, independent feedback control of each eigenmovement is sufficient to provide its stability. Third, the feedback loop in each eigenmovement can be modeled as a linear visco-elastic spring with delay. Visco-elastic parameters and time-delay values result from the combined contribution of passive visco-elastic mechanisms and sensory systems of different modalities     

Antagonism between Ena/VASP proteins and actin filament capping regulates fibroblast motility

Cell motility requires lamellipodial protrusion, a process driven by actin polymerization. Ena/VASP proteins accumulate in protruding lamellipodia and promote the rapid actin-driven motility of the pathogen Listeria. In contrast, Ena/VASP negatively regulate cell translocation. To resolve this paradox, we analyzed the function of Ena/VASP during lamellipodial protrusion. Ena/VASP-deficient lamellipodia protruded slower but more persistently, consistent with their increased cell translocation rates. Actin networks in Ena/VASP-deficient lamellipodia contained shorter, more highly branched filaments compared to controls. Lamellipodia with excess Ena/VASP contained longer, less branched filaments. In vitro, Ena/VASP promoted actin filament elongation by interacting with barbed ends, shielding them from capping protein. We conclude that Ena/VASP regulates cell motility by controlling the geometry of actin filament networks within lamellipodia.     

Ena/VASP proteins contribute to Listeria monocytogenes pathogenesis by controlling temporal and spatial persistence of bacterial actin-based motility

The Listeria monocytogenes surface protein ActA mediates actin-based motility by interacting with a number of host cytoskeletal components, including Ena/VASP family proteins, which in turn interact with actin and the actin-binding protein profilin. We employed a bidirectional genetic approach to study Ena/VASP's contribution to L. monocytogenes movement and pathogenesis. We generated an ActA allelic series within the defined Ena/VASP-binding sites and introduced the resulting mutant L. monocytogenes into cell lines expressing different Ena/VASP derivatives. Our findings indicate that Ena/VASP proteins contribute to the persistence of both speed and directionality of L. monocytogenes movement. In the absence of the Ena/VASP proline-rich central domain, speed consistency decreased by sixfold. In addition, the Ena/VASP F-actin-binding region increased directionality of bacterial movement by fourfold. We further show that both regions of Ena/VASP enhanced L. monocytogenes cell-to-cell spread to a similar degree, although the Ena/VASP F-actin-binding region did so in an ActA-independent manner. Surprisingly, our ActA allelic series enabled us to uncouple L. monocytogenes speed from directionality although both were controlled by Ena/VASP proteins. Lastly, we showed the pathogenic relevance of these findings by the observation that L. monocytogenes lacking ActA Ena/VASP-binding sites were up to 400-fold less virulent during an adaptive immune response.