Stimulation of resting transformed cells (Chang liver cells), prelabeled with [3H] leucine, with fetal calf serum, caused increased nuclear translocation of [3H] nonhistone proteins ([3H] NHP) and DNA synthesis and a parallel inhibition of proteolysis of cellular proteins. [3H] NHP migration was independent of protein synthesis. Fractionation of the nuclear proteins in a pH gradient of 2.5-6.5, showed that [3H] NHP fractions with high degradation rates in resting cells corresponded to the [3H] N H P fractions with high migration rates in stimulated cells, suggesting that degradation and migration of [3H] N H P are linked. Conditioned medium (COM) produced by Chang cells had similar effects as serum, suggesting that factors produced by these transformed cells, control cell growth by a mechanism that is similar to serum. The lysosomotropic amine eserine had similar effects as serum and COM. Based on the similarity of the effects, it would appear that serum and COM inhibit lysoso-ma1 proteolysis. It i s proposed that serum and COM induce N H P migration to the nucleus by inhibiting lysosomal degradation of these proteins. Serum and COM caused also migration of [3H] histones to the nucleus, however the mechanism is not clear.
Nonhistone proteins (NHP) are believed to play a n important role in gene activation and cellular proliferation. The nuclear level of these proteins varies with the Chang liver cells (CH cells) were grown continuously stage of the cell cycle: it is low in resting cells, particu-in plastic bottles of 150 cm2 surface in basal maximum in the early S phase W l f w et al., 1973; each amino acid and 20 m~ hepes; bicarbonate was LeStourgeon et al., 1974;Polet and Spieker-Polet, 1980). added to adjust the pH to 7.2-7.3. This medium was Addition of NHP to nuclei of resting cells alters the supplemented with calf serum. Fetal calf Serum (FCS) and calf serum were from GIBCO, Grand Island, structure of chromatin (Nicolini et al., 1975;Polet and Spieker-Polet, 1980) and increases RNA synthesis (Stein NY. plastic bottles were from corning. H~~~~ and eseret al., 1972). In a previous report (Polet, 1985) it was ine sulfate were from sigma Chemical c0., St. Louis.
shown that the translocation or migration of NHP from [3H] leucine, 55 Ci/mmol, was from ICN, Irvine, CA.
the cytoplasm to the nucleus in lectin-activated lympho-Carrier ampholytes were from pharmacia Fine Chemiproteins. It was proposed that the increase in the nu-agent grade.
clear NHP level observed in lectin-stimulated cells may
MATERIALS AND METHODS
Cells, medium, and chemicals
larly GO cells and gradually rise during G1 to reach a medium (EBM) (Eagle, 1955) that contained 0.4 mM of cYtes is linked to the 'Ysosomal Of these cals, Piscataway, NJ. All other chemicals were of rebe the direct consequence of inhibition of lysosomal degradation of these proteins by the lectin. Alternatively, it