The extracellular matrix modulates the response of PC12 cells to nerve growth factor: cell aggregation versus neurite outgrowth on 3-dimensional laminin substrata.

PC12 cells attach well to plastic culture dishes coated with laminin, collagen, polylysine or a basement membrane extract (2-dimensional substrata) and, in the presence of NGF, extend short neurites within 1-2 days. However, on gels (3-dimensional substrata) reconstituted from a basement membrane extract (RBM), PC12 cells attach extending short processes transiently and within one day, form networks of small aggregates interconnected by process-bearing cells. By 3 days the network collapses into large aggregates that, in media supplemented with NGF, extended a halo of neurites resembling dorsal root ganglia in culture. Time-lapse video recordings indicate that cell motility on RBM gel is accompanied by extensive blebbing as well as extension of processes that attach to and pull together neighbouring cells. These cellular events may contribute to the disruption of the gel underneath aggregates that is apparent when cultures are stained with Coomasie Blue. Ultrastructural studies indicated that aggregates often have zonula adherens-type junctions where cell bodies and processes come in contact. PC12 cells seeded onto gels of laminin alone behave essentially the same as on RBM gels, whereas on collagen gels they behave as on 2-dimensional substrata and extended neurites rather than aggregate. The extent of aggregation increases with greater cell density and is enhanced significantly by NGF. Antisera to NGF reduce the NGF-enhancement of aggregation but do not block aggregation in the absence of NGF. Dibutyryl cAMP or epidermal growth factor, which stimulate process extension and cell division respectively, do not enhance aggregation. However, 3A3, a monoclonal antibody to a laminin/collagen receptor on PC12 cells and antibodies (Fab fragments) to the neural cell adhesion molecule both inhibit cell aggregation.