Control of cyclins, cyclin-dependent kinase inhibitors, p21 and p27, and cell cycle progression in rat hepatocytes by extracellular matrix

Background/Aims: The extracellular matrix plays an essential role in the regulation of cell proliferation in different cell types. However, the regulation of cell cycle control in hepatocytes in response to growth factors and extracellular matrix signals is not well understood. The aims of this study were to investigate the expression of hey cell cycle control elements, including cyclins, A and D1, and cyclin-dependent kinase inhibitors, p21 and p27, in rat hepatocytes in primary culture on dried collagen or Engelbreth-Holm-Swarm in the presence of epidermal growth factor. Methods: Hepatocytes prepared from Wistar rats were cultured on various extracellular matrix in Williams medium E in the presence or absence of 20 ng/ml epidermal growth factor. DNA synthesis was measured by [H-3]thymidine uptake and mRNA expression of cell cycle-related genes was determined by reverse transcription polymerase chain reaction. Results: Cyclins D1 and A mRNA levels were high at the G1/S boundary in epidermal growth factor-stimulated hepatocytes cultured on dried collagen. In contrast to spread cells, hepatocytes cultured on an Engelbreth-Holm-Swarm gel that were prevented from spreading failed to progress through the G1 phase and enter the S phase. This shape-dependent blockage of cell cycle progression correlated with the up-regulation of the cell cycle inhibitors p21 and p27. Conclusions: Changes in hepatocyte-extracellular matrix interactions may control hepatocyte growth within the local microenvironment by modulating cell shape and regulating cyclins and the cyclin-dependent kinase inhibitors p21 and p27.