Astroglial growth factor-2 (AGF2) increases ?-tubulin in astroglial cells cultured in a defined medium

Astroglial cells have been cultured in a defined medium in the presence or not of either astroglial growth factor 2 (AGF2) or dibutyryl cyclic AMP. Immunocytochemical studies showed that AGF2-induced morpohological changes which were very different from those obtained in the presence of the cyclic AMP derivative; retraction of the cell body was much more marked in the presence of AGF2 and the cell processes were much longer and thinner. Labelling of the cells with ?- and ?-tubulin monoclonal antibodies suggested that the tubulin concentration and/or tubulin assembly is stimulated by AGF2. Immunoblot analysis of immature and differentiated astrocytes showed that the ?-tubulin content was increased 2-3 fold by AGF2 whereas for the ?-tubulin the stimulation was much less important (1-2 fold). Such an increase in the expression of ?-tubulin was already important 1 day after addition of AGF2 (2 fold). These and other data suggest that the striking changes in morphology produced by AGF2 might depend at least partly on underlying modifications of the microtubule network.