| Abstract: | Laminin and fibronectin, the major noncollagenous matrix glycoproteins, were studied in connection with normal brain cells and neuroectodermal cell lines. Laminin, a Mr 900,000 dalton matrix glycoprotein and an essential component of basement membranes, was found to be produced by cultured cells of several malignant cell lines of neuroectodermal origin. In cultured mouse C1300 neuroblastoma line cells laminin was localized, by immunoelectron microscopy, to the rough endoplasmic reticulum and, to sites of cell-to-cell and cell-to-substratum adhesion. Further experiments on the intracellular transport of this glycoprotein in C1300 cells confirmed that laminin is, at least partially, transported through the Golgi pathway. These results favor a role for laminin in attachment and cellular interactions of malignant neuronal cells. Laminin was also found in connection with neurons and glial cells from mammalian brain. In primary cultures from developing rat brain the vast majority of non-neuronal cells (80%) expressed immunoreactivity for the glial fibrillary acidic protein, a cytoskeletal protein specific for astrocytes. During the first week in culture all the glial fibrillary acidic protein-positive cells, with the exception of mature-looking star-shaped astrocytes, exhibited immunoreactivity for laminin. The intracellular laminin disappeared gradually after a few weeks in culture, but an extensive laminin matrix persisted and seemed to be localized on the upper surface of the non-neuronal cells. The neurofilament-positive neurons were negative for laminin. Pretreatment of the cultures with the ionophore monensin, caused accumulation of laminin-immunoreactivity within the Golgi region, which confirmed that laminin is, indeed, produced by cultured astrocytes and secreted through the Golgi complex. No fibronectin immunoreactivity was found in the majority of glial cells. However, under culture conditions where fibronectin was omitted from the culture medium there was, in the primary cultures, a minor population of glial fibrillary acidic protein-positive flat glial cells that exhibited intracytoplasmic immunofluorescence for fibronectin. In the presence of fibronectin in culture medium no fibronectin-positive glial cells could be detected. It thus appears that laminin, and to a minor extent fibronectin, are proteins that normal glial cells are capable of producing under specific conditions. Laminin and fibronectin were localized in adult rat brain in capillary and meningeal structures.(ABSTRACT TRUNCATED AT 400 WORDS) |
