Biochemical Characterization of Complexes With p21, a CDK Inhibitor

Progress through the cell cycle requires a concerted interplay between the growth promoting cyclin-dependent kinases CDKs and inhibitors such as p21WAF1 that suppress the CDKs CKIs. Despite the apparent ability of p21 to inhibit CDKs in vitro, its ability to inhibit these kinases in vivo has been a matter of controversy. In addition, while it is known that p21 participates in several complexes with the DNA polymerase processivity factor, PCNA, and cyclin and CDK proteins, it is not clear whether the full complement of p21-associated proteins has been defined. Nor has the function of such multimeric complexes in normal and transformed cells been thoroughly characterized. In light of experiments that indicate an important role for p21 as a downstream target of the p53 checkpoint protein and the observed defective response to DNA damage in mice lacking the p21 gene, it is essential that we understand the role of this protein in normal cells and how perturbations in its expression levels andor function can lead to de-regulated growth. We are therefore attempting to understand the biochemical function of p21 and associated complexes to determine whether de-regulation of complex formation can be associated with transformation of human mammary cells.