NERVE GROWTH-FACTOR (NGF) INDUCES INCREASE IN MULTI-UBIQUITIN CHAINS AND CONCOMITANT DECREASE IN FREE UBIQUITIN IN NUCLEI OF PC12H

Changes in Ubiquitin-immunoreactivity after nerve growth factor (NGF) treatment were investigated in PC12h cells. Ubiquitin-immunoreacitivit y was increased in the nucleus of NGF-treated cells. The quantitative analysis revealed that, after 7 days of NGF treatment, almost 20% of c ells had ubiquitin-immunoreactive nuclei and the frequency was increas ed thereafter. Levels of free ubiquitin and multi-ubiquitin chains wer e measured by radioimmunoassay (RIA) and enzyme-linked immunosorbent a ssay (ELISA), respectively. Measurements were carried out for four sub cellular fractions: urea- and water-soluble extracts of nuclei and cyt oplasm. Decrease in free ubiquitin was observed in water-soluble cytop lasmic extracts of NGF-treated cells, though increase in multi-ubiquit in chains in the same fraction was not observed. As for nuclei, increa se in multi-ubiquitin chains and concomitant decrease in free ubiquiti n were found in the water-soluble extracts after NGF treatment. Levels of multi-ubiquitin chains did not change in urea-soluble cytoplasmic extracts as well as nuclear urea-soluble ones after NGF treatment. The se results indicated that multi-ubiquitination of nuclear proteins is increased during NGF-induced neuronal differentiation of PC12h cells. Copyright (C) 1996 Elsevier Science Ireland Ltd