Figure 4.

v-PL promotes re-entry in the cell cycle of confluent resting cells. Upper panel: confluent growth-arrested chondrocytes, obtained from cartilage biopsies and expanded in vitro in the presence of 10% FCS, were maintained in 10% serum or additionally supplemented with 5% v-PL. A crystal violet proliferation assay was performed in parallel on both cultures. Confluent cells treated with v-PL resumed proliferation, whereas the parallel control culture did not. Lower panel: Western blot analysis of proteins extracted from the cells treated with 5% PL probed with Cyclin D1, phospho Akt, phospho Erk1/2, and Actin antibodies shows that proliferation pathways were activated by v-PL also in the absence of serum. Number (n) of cell cultures used for the experiments is indicated on the graph for each cell type.