PHENOTYPIC HETEROGENEITY OF OSTEOBLAST-LIKE MC3T3-E1 CELLS - CHANGES OF BRADYKININ-INDUCED PROSTAGLANDIN E(2) PRODUCTION DURING OSTEOBLAST MATURATION

We have examined clonal murine calvarial MC3T3-E1 cells obtained from different sources to compare their osteoblastic features (alkaline pho sphatase [ALP], cyclic adenosine monophosphate [cAMP] response to para thyroid hormone, prostaglandin E(2) (PGE(2)) and PGE(1), bradykinin-in duced production of PGE(2)), It was found that the sublines investigat ed showed large variation of the above-mentioned parameters, which may be attributed to distinct differentiated stages of osteoblast develop ment, Increase of ALP activity was paralleled by an increase in cAMP a ccumulation in response to the above-mentioned agents, The most striki ng difference was observed with bradykinin-induced production of PGE(2 ). Early stage cells (low ALP) produced high levels of PGE(2), whereas cells with high ALP activity showed no bradykinin stimulation at all, This,vas consistent with the results of specific binding of H-3-brady kinin to its receptor and also correlated well with the bradykinin-ind uced signal transduction sequence (inositol triphosphate liberation an d elevation of intracellular calcium levels), This was confirmed by No rthern blot analysis of bradykinin receptor mRNA expression, These res ults indicate that the widely used osteoblast-like cell line MC3T3-E1 is synonymous for multiple sublines, representing different stages of osteoblast development, These sublines were most likely emerging from the early stage cell line due to the applied culture conditions, Moreo ver, distinct biochemical features are displayed in correlation to the differentiation stage, thus providing a useful model to study the mol ecular mechanism of osteoblast maturation.