Mechanisms of cytoskeletal regulation. Modulation of aortic endothelial cell spectrin by the extracellular matrix

Abstract

Endothelial cells have a complex cytoskeleton that is responsive to a variety of stimuli such as shear and desquamative injury. The extracellular matrix is known to influence several aspects of cellular behavior, including attachment, spreading, and migration and may, in part, initiate and control vascular responses in growth, differentiation, wound repair, and neoplasia. It is likely that linkage between surface receptors responsible for sensing the matrix and the cytoskeleton may be relevant to understanding the mechanisms of these responses. Spectrin is a high-molecular-weight heterodimer recently identified in many cells that appears to link surface receptors to cortical actin filaments. We have confirmed the existence of spectrin in cultured aortic endothelial cells by metabolic labeling and immunoprecipitation and demonstrated that its organization and intracellular distribution is sensitive to the extracellular matrix. When bovine calf aortic endothelial cells (BAEC) are cultured to confluency on a fibronectin (Fn) substrate, they assume a flattened, spread morphology and exhibit a punctate spectrin distribution with no discernible peripheral localization. In contrast, BAECs cultured on a Type I/III collagen (I/III) substrate exhibit a fibrillar spectrin pattern with significant peripheral localization. When migrating cells were examined, the distribution of spectrin was strikingly different. The cells on the Fn substrate showed no changes in spectrin localization, whereas the cells on I/III exhibited a significant rearrangement, with spectrin being in a coarse fibrillar form, with the fibrils aligned parallel to the direction of migration. The differences in arrangement of this cytoskeletal component on the two substrata reflect the ability of the substrate to perturb the cytoskeletal organization and modulate some aspects of cell behavior such as spreading, proliferation, and migration. These data are consistent with the concept that the nonerythroid spectrins may function as transducers of information from membrane receptors to the cytoskeleton.