Serum or Growth Factor Deprivation Induces the Expression of Alkaline Phosphatase in Human Gingival Fibroblasts

Abstract

We have previously reported that the increased expression of alkaline phosphatase (ALP) activity is a phenotypic characteristic of gingival fibroblasts present in chronic inflammatory periodontal lesions. We hypothesized that ALP might be induced in gingival fibroblasts by environmental factors. In the present study, we investigated the factors influencing the induction of ALP expression in fibroblasts derived from healthy human gingiva. The withdrawal of serum from confluent cultures of fibroblasts increased the number of cells positive for ALP activity and protein, without their proliferation. Suramin, a growth factor antagonist, induced ALP expression in cells cultured with serum. Serum re-addition or exposure to platelet-derived growth factor-AB and/or insulin-like growth factor I suppressed ALP induction and caused cell growth. ALP-positive cells could survive for up to 6 weeks after serum deprivation, a condition inducing cell death via apoptosis. These results demonstrate that serum or growth factor deprivation induces the expression of ALP in gingival fibroblasts. ALP expression is negatively correlated with cell growth and accompanied by a change into serum-growth-factor-independent survival.