RRAS may promote noncartilaginous procollagen gene expression by enhancing AKT phosphorylation. (a), (b) lacZ or a constitutively active (CA) or dominantly negative (DN) mutant of RRAS was overexpressed in monolayer-cultured chondrocytes by means of adenoviral gene transfer. Three days later, phosphorylation of AKT at Ser473 was evaluated (a), and expression of type I procollagen (COL1A1) and type III procollagen (COL3A1) was determined by quantitative PCR (b). (c), (d) siRNA for RRAS (RRAS) or control siRNA was introduced into chondrocytes, and three days later, phosphorylation of AKT (c) and expression of indicated procollagen genes was evaluated (d). Two siRNAs for RRAS were used for the experiments. (a), (c) Representative results of five independent experiments are shown. (b), (d) Results are shown by relative ratios against values shown by open bars. Results are mean ± standard error of the mean of four (d) or six (b) independent experiments, each in triplicate. *P <0.05, **P <0.01. GADPH, glyceraldehyde 3-phosphate dehydrogenase.