In this report, we identified the novel protein heart protein phosphatase 1-binding protein (Hepp1), encoded by FLJ23654. Hepp1 associated with protein phosphatase 1 (PP1) by yeast two-hybrid, GST pull-clown, co-immunoprecipitation, and far Western blotting assays Northern blot analysis revealed that Hepp1 mRNA was only expressed in human heart and testis Recombinant Hepp1 slightly enhanced the enzymatic activity of PP1 and antagonized the ability of phospho-inhibitor-1 or inhibitor-2 to inhibit PP1 Hepp1 protein in human heart tissues was detected by Western blot analysis. Together. our data suggest that Hepp1 can play a role in cardiac functions by working in concert with PP1. (C) 2009 Elsevier Inc. All rights reserved