The helix‐loop‐helix transcription factors Id1 and Id3 have a functional role in control of cell division in human normal and neoplastic chondrocytes

The expression and localization of the helix-loop-helix transcription factors Id1 and Id3, as well as localization of the E12-protein, were studied in cells isolated from human articular cartilage and chondrosarcoma. Serum withdrawal down-regulated Id1 and Id3 expression in chondrocytes but not the Id1 expression in chondrosarcoma cells. Antisense oligonucleotides directed against Id1 and Id3 decreased BrdU labeling in both cell types. E12 was localized to the nucleus in chondrocytes and non-confluent tumor cells and in confluent tumor cells, E12 had a cytoplasmic localization. This study suggests a functional role for Id1 and Id3 in the control of proliferation and differentiation of cartilage.