P53 and Akt expression during osteoblast differentiation.
Department of Biochemistry, Chicago College of Osteopathic Medicine, Midwestern University, Downers Grove, IL, United States
During osteoblast differentiation, a number of proteins involved in apoptosis and cell cycle are expressed. We have previously shown p53 to have a specific role in this process, by its ability to regulate the expression of bone specific differentiation related protein osteocalcin. In order to further understand the importance of p53 in differentiation and how this process relates to an environment where expression of apoptosis genes and cell cycle arrest genes persist, we investigated the role of survival factor Akt. Akt is a protein known to regulate p53 activity and its expression in relationship to p53 was determined during in vitro osteoblast differentiation. We found p53 levels rise and fall during the time intervals tested. Akt levels were analyzed by RT-PCR as well as by western blotting. Akt levels showed a response similar to that of p53, except in the fact that the expression of the two were reciprocal. The change seen in Akt mRNA expression was mirrored at the level of protein. There was also a corresponding increase in the level of phosphorylated Akt during the time intervals when total Akt was up. We used a murine osteosarcoma cell line stably expressing a temperature sensitive p53 in order to demonstrate if wild type p53 function was important to prevent the increase in Akt. The functional relationship between p53, Akt and bone specific markers will be discussed.
Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Nice, France; February 7 - 10, 2004; in poster session 896 (Tumor suppressor genes).