The effect of dibutyryl cyclic AMP on the expression of actin isoforms in astroglia

Mammalian cells contain at least 8 actin isoforms. The functional significance and the mechanisms that regulate the expression of each actin isoform are not yet known. Using immunofluorescence staining, it was found that all astroglia in tissue culture express beta-actin isoform and about 86% of astroglia express alpha-smooth muscle actin isoform. When astroglia were treated with dibutyryl cyclic AMP for 4, 7, 14 and 21 days, it was found that the number of the cells expressing alpha-smooth muscle actin isoform progressively decreased, whereas, the number of the cells expressing beta-actin isoform remained constant. The western blot experiment showed that the amount of total alpha-smooth muscle actin isoform (soluble and insoluble) and of the insoluble isoform expressed by astroglia treated with dibutyryl cAMP decreased whereas, the amount of total and insoluble beta-actin isoform expressed by the same cells did not show any significant changes. The cells treated with the cAMP failed to migrate and to close the area created by the scratch wound in monolayer culture. However, the non-treated cells migrated and closed the area created by the scratch after 3 days. This study shows that the astroglia have different mechanisms in regulating the expression of different actin isoforms and that the alpha-sm actin isoform is important in migration of astroglia.