ANNEXIN II2-P11(2) (CALPACTIN-I) STIMULATES THE ASSEMBLY OF GFAP IN ACALCIUM-DEPENDENT AND PH-DEPENDENT MANNER

Annexin II2-p11(2) (calpactin I) was tested as a potential regulator o f GFAP assembly into glial filaments (GF), following the observation t hat it interacts with GFAP and cosediments with GF in a sedimentation assay. Under conditions where GFAP assembly is reduced, e.g.,at pH val ues > 6.8, annexin II2-p11(2) stimulates GF formation in a Ca2+- and d ose-dependent manner. Concomitantly, an ever larger fraction of annexi n II2-p11(2) can be recovered in GF pellets as the pH is raised from 6 .8 to 7.35. Monomeric annexin II also stimulates GFAP assembly, althou gh with a smaller efficacy as compared to annexin II2-p11(2), but does not cosediment with GF to a large extent, whereas pll neither cosedim ents with GF nor affects GFAP assembly. On the other hand, the in vitr o reconstituted annexin II2-p11(2) heterotetramer mimics native annexi n II2-p11(2), and perturbation of the integrity of annexin II2-p11(2) by a mild treatment with a-chymotrypsin results in the nearly complete abolition of the stimulatory effect of annexin II2-p11(2) on GFAP ass embly. These data suggest that annexin II2-p11(2) might be involved in the regulation of the state of assembly of GF, possibly in concert wi th other proteins. (C) 1995 Academic Press, Inc.