MT1-MMP is a potent invasion-promoting membrane protease employed by aggressive cancer cells. MT1-MMP localizes preferentially at membrane protrusions called invadopodia where it plays a central role in degradation of the surrounding extracellular matrix (ECM). Previous reports suggested a role for a continuous supply of MT1-MMP in ECM degradation. However, the turnover rate of MT1-MMP and the extent to which the turnover contributes to the ECM degradation at invadopodia have not been clarified. To approach this problem, we first performed FRAP (Fluorescence Recovery after Photobleaching) experiments with fluorescence-tagged MT1-MMP focusing on a single invadopodium and found very rapid recovery in FRAP signals, approximated by double-exponential plots with time constants of 26 s and 259 s. The recovery depended primarily on vesicle transport, but negligibly on lateral diffusion. Next we constructed a computational model employing the observed kinetics of the FRAP experiments. The simulations successfully reproduced our FRAP experiments. Next we inhibited the vesicle transport both experimentally, and in simulation. Addition of drugs inhibiting vesicle transport blocked ECM degradation experimentally, and the simulation showed no appreciable ECM degradation under conditions inhibiting vesicle transport. In addition, the degree of the reduction in ECM degradation depended on the degree of the reduction in the MT1-MMP turnover. Thus, our experiments and simulations have established the role of the rapid turnover of MT1-MMP in ECM degradation at invadopodia. Furthermore, our simulations suggested synergetic contributions of proteolytic activity and the MT1-MMP turnover to ECM degradation because there was a nonlinear and marked reduction in ECM degradation if both factors were reduced simultaneously. Thus our computational model provides a new in silico tool to design and evaluate intervention strategies in cancer cell invasion.
Signal transduction in rod cells begins with photon absorption by rhodopsin and leads to the generation of an electrical response. The response profile is determined by the molecular properties of the phototransduction components. To examine how the molecular properties of rhodopsin correlate with the rod-response profile, we have generated a knock-in mouse with rhodopsin replaced by its E122Q mutant, which exhibits properties different from those of wild-type (WT) rhodopsin. Knock-in mouse rods with E122Q rhodopsin exhibited a photosensitivity about 70% of WT. Correspondingly, their single-photon response had an amplitude about 80% of WT, and a rate of decline from peak about 1.3 times of WT. The overall 30% lower photosensitivity of mutant rods can be explained by a lower pigment photosensitivity (0.9) and the smaller single-photon response (0.8). The slower decline of the response, however, did not correlate with the 10-fold shorter lifetime of the meta-II state of E122Q rhodopsin. This shorter lifetime became evident in the recovery phase of rod cells only when arrestin was absent. Simulation analysis of the photoresponse profile indicated that the slower decline and the smaller amplitude of the single-photon response can both be explained by the shift in the meta-I/ meta-II equilibrium of E122Q rhodopsin toward meta-I. The difference in meta-III lifetime between WT and E122Q mutant became obvious in the recovery phase of the dark current after moderate photobleaching of rod cells. Thus, the present study clearly reveals how the molecular properties of rhodopsin affect the amplitude, shape, and kinetics of the rod response.Light absorption by rhodopsin in rod photoreceptor cells results in the activation of a G protein-mediated signal transduction cascade that eventually generates an electrical response (1). The key proteins in this cascade have been identified, and their molecular properties as well as interactions with each other have been extensively investigated (2, 3). A current question is how well these properties and interactions correlate with the response profile of the photoreceptor cells. Although the gene knock-out approach has been very useful in addressing this question for the proteins rhodopsin kinase and arrestin (4, 5), this strategy is less appropriate for rhodopsin and G protein, because the deletions of these proteins eliminated the light response (6, 7). The gene knock-in approach is an alternative way, with a mutant protein replacing the wild-type (WT) 8 version. The maintenance of the same expression level of the protein in this procedure is important, because the interpretation can be difficult otherwise. For example, the photoresponse profile is altered when the rhodopsin content in rods is halved (8, 9).Our past work on comparing rhodopsin and cone pigments (10) has shown that their photosensitivities are not so different, but the meta-II (the G protein-activating state), as well as the subsequent meta-III, intermediates of cone pigments exhibit faster decay than those of rhodopsi...
Nine patients with pure dysarthria underwent computed tomography or magnetic resonance imaging. Eight patients had infarcts of lacunar or larger size in the internal capsule: four in the superior portion of the anterior limb or adjacent corona radiata and four in the superior portion of the genu or the adjacent corona radiata. In one patient, there was a small infarct in the bulbar motor cortex. Dysarthria was transient and characterized by poor articulation in all cases. Five patients also had contralateral facial weakness, and three patients with lesions in the genu had minimal and transient involvement of the contralateral fingers. These three cases appeared to be variants of the dysarthria-clumsy hand syndrome. We submit that this syndrome should sometimes be regarded as a stroke syndrome rather than always as a lacunar syndrome. (Stroke 1991^2:809-812)
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