Juárez, Melina

Microtubule associated proteins (MAPs) play an important role in microtubule assembly. In an earlier study we showed that phosphorylation of microtubule binding region of MAP‐2 (MTBR; a peptide containing conserved repeat region of MAPs) by Glycogen Synthase Kinase‐3β (GSK‐3β) inhibits its ability to assemble microtubules (Teel et. el. The FASEB Journal 11, A1352, 1997). In the present study we studied the effects of phosphorylation of MAPs on their O‐glycosylation. Two isomers of β‐N‐acetylglucosaminyl transferase (OGT); short OGT (sOGT), and nucleoplasmic (ncOGT) were used. The ncOGT showed greater activity toward MAP‐2c, Tau‐4R, and MTBR. The MTBR and Tau‐4R were pre‐incubated with protein kinase A (PKA) or PKA followed by GSK‐3β, and then incubated with ncOGT and UDP‐[ 3 H]N‐Acetylglucosamine. The incorporation of 3 H into these pre‐phosphorylated proteins show that phosphorylation by PKA inhibits their O‐glycosylation by ~50%. Subsequent phosphorylation by GSK‐3β decreases their O‐glycosylation further by ~90%. We conclude that phosphorylation and O‐glycosylation may be competing for the same sites on MTBR and Tau‐4R and thus may play an important role in the regulation of microtubule assembly. (Supported by NIH‐RISE Grant #07298409)