Change in gene expression subsequent to induction of Pnn/DRS/memA: Increase in p21^cip1/waf1

Pnn (PNN) is a nuclear and cell adhesion-related protein. Previous work has suggested that Pnn/DRS/memA is a potential tumor suppressor involved in the regulation of cell adhesion and cell migration. Using the ecdysone-inducible mammalian expression system, a stable inducible GFP-tagged human Pnn gene (PNNGFP) expressing 293 cell line was created (EcR293-PNNGFP). Cells induced to express PNNGFP not only exhibited increased cell-cell adhesion but also exhibited changes in cell growth and cell cycle progression. cDNA array analyses, together with real time PCR, revealed that the effects of exogenously expressed Pnn on cellular behavior may be linked to the regulation of the expression of specific subset genes. This subset includes cell cycle-related genes such as p21^cip1/waf1, CDK4, CPR2; cell migration and invasion regulatory genes such as RhoA, CDK5, TIMP-1, MMP-7, and EMMPRIN; and MIC-1. Concordant with previous observations of Pnn-induced phenotype changes, genes coding for epithelial associated processes and cell division controls were elevated, while those coding for increased cell motility and cellular reorganizations were down-regulated. We utilized p21 promoter-luciferase reporter constructs and demonstrated that a marked stimulation of p21 promoter activity in 293 cells correlated with increased Pnn expression. Taken together, these data indicate that Pnn may participate in the regulation of gene expression, thereby, positively promoting cell-cell adhesion, and negatively affecting cell migration and cell proliferation.