Abstract：cAMP-dependent protein kinase β inhibitors (PKIB) are discovered as a new class of heatresistant endogenous proteins in human that inhibit the kinase activity. To investigate the function of PKIB in senescent cells, long-cultured 2BS diploid fibroblast from human fetal lung was used as the experimental subject and compared with the cells with less passages. The PKIB expression was higher in senescent cells as determined by real time-PCR and lead to only limited activation of cAMP-dependent protein kinase after treated with PKA-activator Forskolin. The ability of PKIB binding to PKA catalytic subunit was reduced comparing to young cells as shown by immunoprecipitation. The PKIB overexpression in the young cells significantly reduced the cAMPdependent protein kinase activity, while the amount of PKA catalytic subunit was similar in both old and young cells as confirmed by Western blotting. These result suggested that the inhibition of cAMP-dependent protein kinase might be associated with cell senescence.
