SELECTIVE UPTAKE AND DEGRADATION OF C-FOS AND V-FOS BY RAT-LIVER LYSOSOMES

The transcription factor c-Fos is a short-lived protein and calpains a nd ubiquitin-dependent systems have been proposed to be involved in it s degradation, In this report, we consider a lysosomal degradation pat hway for c-Fos. Using a cell-free assay, we have found that freshly is olated lysosomes earn take up and degrade c-Fos with high efficiency. v-Fos, the oncogenic counterpart of c-Fos, can also be taken up by lys osomes, yet the amount of incorporated protein is much lower. c-Fos up take is independent of its phosphorylation state but it appears to be regulated by dimerization with differentially phosphorylated forms of c-Jun, while v-Fos escapes this regulation, Moreover, we show that c-F os is immunologically detected in lysosomes isolated from the liver of rats treated with the protease inhibitor leupeptin, Altogether, these results suggest that lysosomes can also participate in the selective degradation of c-Fos in rat liver.