IN ISOLATED HUMAN CENTROSOMES, THE ASSOCIATED KINASES PHOSPHORYLATE ASPECIFIC SUBSET OF CENTROSOMAL PROTEINS

Several studies have shown that kinases and phosphatases can interact with the centrosome during interphase and mitosis suggesting that cent rosomal components might be the targets of these enzymes. The associat ion of the cAMP-dependent protein kinase type II and the mitotic kinas e p34(cdc2) With centrosomes from human lymphoblast cells has previous ly been shown (Keryer et al, 1993, Exp Cell Res 204, 230-240; Bailly e t al, 1989, EMBO J 8, 3985-3995). In this paper we demonstrate that is olated centrosomes are able to phosphorylate a few number of centrosom al proteins (M(r) 230-220000; 135000 and 50000) and also I-Il histone. The phosphorylation of H1-histone is cell cycle dependent and modulat ed by phosphatases. The use of kinase and phosphatase inhibitors and t he addition of the catalytic subunit of cAMP-dependent kinase or of cy clinB-p34(cdc2) kinase showed that both kinases phosphorylate the same centrosomal substrates. In addition two centrosomal proteins (M(r) 10 0000 and 37000) were phosphorylated only by p34(cdc2) kinase. Although the low amount of centrosomal proteins precluded a full characterizat ion of these substrates we discuss the identity of the major centrosom al phosphoproteins by comparison with proteins known to associate with microtubule-organizing centres or mitotic spindles. Our results raise also the intriguing possibility that the cAMP-dependent protein kinas e could be regulated by the mitotic kinase at the entry of mitosis.