Cell cycle regulated expression and phosphorylation of hpttg proto-oncogene product

We recently isolated a cDNA for hpttg, the human homolog of rat pituitary t umor transforming gene, Now we have analysed the expression of hpttg as a f unction of cell proliferation. hPTTG protein level is up-regulated in rapid ly proliferating cells, is down-regulated in response to serum starvation o r cell confluence, and is regulated in a cell cycle-dependent manner, peaki ng in mitosis, In addition, we show that hPTTG is phosphorylated during mit osis. Immunodepletion and in vitro phosphorylation experiments, together wi th the use of a specific inhibitor, indicate that Cdc2 is the kinase that p hosphorylates hPTTG. These results suggest that hpttg is induced by, and ma y have a role in, regulatory pathways involved in the control of cell proli feration.