Regulation of the profibrotic and angiogenesis modulating cytokine connective tissue growth factor (CTGF) occurs primarily at the transcriptional level. Therefore, we hypothesized that histone deacetylating enzymes (HDAC), which modulate the accessibility of transcriptionally active promoter regions, might play a role in the regulation of CTGF gene expression. We analyzed microvascular endothelial cells, which showed immunoreactivity for acetylated histone in kidney sections, and compared them with renal tubular epithelial cells. Treatment of cultured endothelial cells with different HDAC inhibitors up-regulated CTGF mRNA and protein. Pre-treatment with HDAC inhibitors facilitated induction of CTGF by transforming growth factor-beta (TGF-beta) or lysophosphatidic acid. Transcription factors of the FoxO family were involved in the up-regulation of CTGF as shown at protein level and by reporter gene analyses. In tubular epithelial cells, up-regulation of CTGF was only observed when these cells were cultured as subconfluent cells. Dense cells, which are more likely to resemble tubular cells in vivo, showed no up-regulation upon treatment with HDAC inhibitors and were protected against CTGF induction by TGF-beta. Taken together, our data indicate that the effect of HDAC inhibitors on CTGF expression is largely cell dependent in non-tumour cells. Different cell type-specific transcription factors seem to determine whether CTGF expression is reduced or increased in cells exposed to HDAC inhibitors.