INDUCTION OF PROTEIN DISULFIDE-ISOMERASE DURING PROLIFERATION ARREST AND DIFFERENTIATION OF SH5Y NEUROBLASTOMA-CELLS

The relationship of genes associated with contact inhibition of cell g rowth and the commitment for differentiation was studied in the human neuroblastoma cell line SH5Y. These cells could be induced to differen tiate in vitro into neuronal-like cells upon incubation with retinoic acid, an event that was accompanied by an enhancement in levels of neu ron-specific acetylcholinesterase. The kinetics of differentiation, ba sed on morphology and acetylcholinesterase levels, showed that prolife ration arrest always preceeded differentiation and may be a prerequisi te for differentiation. To determine if this growth arrest is mediated by the same pathway underlying contact inhibition of proliferation, t he expression of a gene associated with the induction of contact inhib ition, protein disulfide isomerase (PDI), was quantified by Northern b lot analysis and enzymatic activity after retinoic acid treatment. Ret inoic acid caused a significant elevation of PDI-mRNA within 24 hrs. a fter treatment with a corresponding increase in enzyme activity which immediately preceeded proliferation arrest and differentiation. Bacitr acin, a specific inhibitor of PDI, abrogated the ability of retinoic a cid to induce differentiation. However, treatment with interferon also increased PDI activity and caused proliferation arrest and SH5Y diffe rentiation but into a fibroblastoid cell without neurite outgrowth. Th ese results suggest that the commitment for differentiation of SH5Y ce lls involves a form of proliferation arrest in which activation of PDI activity is a required and early event but one that does not determin e the final differentiation pathway.