The HIPK2 protein is a member of a recently identified family of nuclear protein kinases that interact with homeodomain transcription factors and that are well conserved in various organisms. HIPK2 acts as a transcriptional co-repressor of homeoproteins and it is a component of a co-repressor complex containing Groucho and a histone deacetylase. We have recently demonstrated that the HIPK2 protein interacts with HMGA1 proteins in vitro and in vivo and that HIPK2 exerts a potent inhibitory effect on the cell growth of different normal cell lines. Here we demonstrate that the HIPK2 gene is expressed during the latest phases of embryogenesis, and preferentially in retina, in muscle and in neural tissues. Conversely, HIPK2 is ubiquitously expressed in murine and human adult tissues. We have also found that HIPK2 expression is reduced in breast and thyroid carcinomas, suggesting a role of this gene in the process of carcinogenesis. (C) 2002 Elsevier Science (USA).