Plakophilin 1 (PKP1) is a member of the arm-repeat (armadillo) and plakophilin gene families and it is an essential component of the desmosomes. Plakophilin 1 (PKP1) belongs to the arm-repeat protein family which is characterized by the presence of a conserved 42-amino-acid motif. Despite individual members of the family containing a similar type of structural domain, they exhibit diverse cellular functions. PKP1 is ubiquitously expressed in human tissues and, depending on the type of cell, found prominently in the karyoplasm and/or in desmosomes. PKP1 is an important plaque component of desmosomes, major intercellular adhesive junctions that act as anchorage points for intermediate filaments. Abnormal expression of PKP1 was observed in various types of cancer.