IN-VITRO PHOSPHORYLATION OF CYTOSKELETAL PROTEINS IN THE RAT CEREBRAL-CORTEX IS DECREASED BY PROPIONIC-ACID

In the present study we demonstrate that propionic acid (PA), a metabo lite that accumulates in large amounts in propionic acidemia, is able to decrease in vitro incorporation of [P-32]ATP into neurofilament sub units (NF-M and NP-L) and alpha- and beta-tubulin. Considering that th e endogenous phosphorylating system associated with the cytoskeletal f raction contains cAMP-dependent protein kinase (PKA), Ca2+/calmodulin protein kinase II (CaMKII), and protein phosphatase 1 (PPI), we first assayed the effect of the acid on the kinase activities by using the s pecific activators cAMP and Ca2+/calmodulin or the inhibitors PKAI or KN-93 for PKA and CaMKII, respectively. Results demonstrated that the acid totally inhibited the stimulatory effect of cAMP and interfered w ith the inhibitory effect of PKAI. In addition, PA partially prevented the stimulatory effect of Ca2+/calmodulin and interfered with the eff ect of KN-93. In addition, we demonstrated that PA totally inhibited i n vitro dephosphorylation of neurofilament subunits and tubulins media ted by PP1 in brain slices pretreated with the acid. Taken together, t hese result-a demonstrate that PA inhibits the in vitro activities of PRA, CaMKII, and PPI associated with the cytoskeletal fraction of the cerebral cortex of rats, This study suggests that PA at the same conce ntrations found in tissues from propionic acidemic children may alter phosphorylation of cytoskeletal proteins, which may contribute to the neurological dysfunction characteristic of propionic acidemia. (C) 199 7 Academic Press.