ABSTRACT
The non-transmembrane protein tyrosine phosphatase, PTP-S, is located predominantly in the cell nucleus in association with chromatin. Here we have analysed the expression of PTP-S upon mitogenic stimulation and during cell division cycle. During liver regeneration after partial hepatectomy, PTP–S mRNA levels increased 16-fold after 6 h (G1 phase) and declined thereafter. Upon stimulation of serum starved cells in culture with serum, PTP-S mRNA levels increased reaching a maximum during late G1 phase and declined thereafter. No significant change in PTP-S RNA levels was observed in growing cells during cell cycle. PTP–S protein levels were also found to increase upon mitogenic stimulation. Upon serum starvation for 72 h, PTP–S protein disappears from the nucleus and is seen in the cytoplasm; after 96 h of serum starvation the PTP-S protein disappears from the nucleus as well as cytoplasm. Refeeding of starved cells for 6 h results in reappearance of this protein in the nucleus. Our results suggest a role of this phosphatase during cell proliferation.