Cultured human retinal pigment epithelial cells differentially express thrombospondin-1,-2,-3, and-4

Thrombospondins are a family of at least five proteins (TSP-1 to -4 and car tilage oligomeric matrix protein or COMP) whose functions are indeterminate . Distribution differences between family members suggest each protein may have some distinct functions. The retinal pigment epithelium (RPE) has dive rs unusual roles for an epithelia and can produce TSP-1. However, the wide range of RPE activities suggests that, if different thrombospondin family m embers do have different functions, RPE may express thrombospondins additio nal to TSP-1. Therefore, we analysed expression of thrombospondin isoforms by RPE using reverse-transcription-linked polymerase chain reaction. Cultur ed cells exhibited differential expression of TSP-1 to -4; TSP-2 and TSP-4 appearing later in culture than TSP-1 and TSP-3. In situ RPE expressed mRNA for TSP-1 to -4. No COMP mRNA was detected in RPE. These observations sugg est that thrombospondin isoforms are regulated differently by the cells and that these proteins may have different functions in the RPE. (C) 2000 Else vier Science Ltd. All rights reserved.