Kinetic analysis of 'rapid onset' neurite formation in NG108-15 cells reveals a dual role for substratum-bound laminin.

Undifferentiated neural hybrid NG108-15 cells plated on laminin-coated, polylysine-treated plastic Petri dishes in minimal serum-free media formed long neurites within 1-4 h post-plating. Morphologic features and pharmacologic responses of these 'rapid onset' neurites were strikingly similar to those of neuronal growth cones. Cycloheximide (1-10 micrograms/ml) and forskolin (10(-7) to 10(-6) M) accelerated the initial formation of laminin-stimulated neurites, but did not cause rapid onset neurites to emerge upon Petri dishes coated with polylysine alone. Quantitative study of the substratum-dependent effect of cycloheximide showed that it was additive even with maximally effective amounts of laminin, independent of the magnitude of the laminin-stimulated baseline rate and not limited by an inherent ceiling in the rate at which neurites could form. The methylation inhibitor 5'-deoxy-5'-methyl thioadenosine (MTA) (3 X 10(-4) to 3 X 10(-3) M) did stimulate neurites to form on polylysine. MTA- and laminin-stimulated neurites were similar in their susceptibility to calmodulin antagonists and the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA). However, formation of MTA-stimulated neurites was not accelerated by cycloheximide. A simple two-compartment kinetic model of 'rapid onset' neurite formation is proposed: compartment A is common to both laminin- and MTA-stimulated neurites. Compartment B is affected by cycloheximide, and its access to the neurite formation machinery contained in compartment A is gated according to the nature of the substratum. In addition to its direct effects, laminin controls the relative dominance of the two kinetic compartments via modulating the effectiveness of other signals acting upon an endogenously active compartment B.