INHIBITION OF PROTEIN-KINASE-C ACTIVITY IN MUCOLIPIDOSIS TYPE-4 - A MODEL FOR A NEW PATHOGENETIC MECHANISM IN INBORN-ERRORS OF METABOLISM

Inhibition of protein kinase C [PK-C] activity by sphingosine and its derivatives has been suggested to play a role in the pathogenesis of s phingolipidoses. In the present study, PK-C activity and PK-C-mediated phosphorylation of endogenous substrates were studied in skin fibrobl asts from patients with mucolipidosis type 4 [ML-4], in which there is accumulation of the phospholipids phosphatidylcholine, lysophosphatid ylcholine, phosphatidylethanolamine as well as gangliosides. Cytosolic PK-C activity in 5 ML-4 cell lines was comparable to that in control cells. PK-C activity in the particulate fraction of these cells was 84 +/- 14 pmol P-32/mg protein per min compared with 267 +/- 26 in contr ol cells. Increasing the concentrations of the activating lipids in th e reaction mixture did not enhance PK-C activity in ML-4 cells, sugges ting a non-competitive inhibition of the kinase. Following partial pur ification of the enzyme from the particulate fraction PK-C activity in creased to 288 +/- 14 and 339 +/- 12 pmol P-32/mg protein per min in M L-4 and control cells, respectively. The phosphorylation pattern of en dogenous substrates in the particulate fraction of ML-4 cells differed from that in control cells both in the absence and in the presence of calcium and activating lipids. We suggest that PK-C may be involved i n the pathogenesis of sphingolipidoses and that this may represent an example for a new type of pathogenetic mechanisms in inborn errors of metabolism.