Extracellular matrix and growth factors are the crucial factors that regulate healing and regenerating processes in human periodontal ligament cells. The purpose of this study was to examine the effects of type I collagen and insulin-like growth factor-I (IGF-I) on osteopontin (OPN) expression. The data showed that OPN expression was significantly decreased when cells were cultured on collagen-coated plates. Addition of IGF-I obviously induced OPN expression only in a collagen-coated condition, suggesting an attenuating effect of IGF-I on the decrease of OPN expression. Cells treated with a combination of inhibitory antibody to beta 1 integrin and IGF-I showed the same level of OPN expression as those treated with either inhibitory antibody to beta 1 integrin or IGF-I alone. These results indicate that IGF-I counteracts with the inhibitory signal from type I collagen through l integrin receptor. (c) 2005 Elsevier Inc. All rights reserved.