Pleiotrophin regulates serine phosphorylation and the cellular distribution of β-adducin through activation of protein kinase C

Pleiotrophin (PTN) was found to regulate tyrosine phosphorylation of β-adducin through the PTN/receptor protein tyrosine phosphatase (RPTP)β/ζ signaling pathway. We now demonstrate that PTN stimulates the phosphorylation of serines 713 and 726 in the myristoylated alanine-rich protein kinase (PK) C substrate domain of β-adducin through activation of either PKC α or β. We also demonstrate that PTN stimulates translocation of phosphoserine 713 and 726 β-adducin either to nuclei, where it associates with nuclear chromatin and with centrioles of dividing cells, or to a membrane-associated site, depending on the phase of cell growth. Furthermore, we demonstrate that PTN stimulates the degradation of β-adducin in PTN-stimulated cells. Phosphorylation of serines 713 and 726 in β-adducin is known to markedly reduce the affinity of β-adducin for spectrin and actin and to uncouple actin/spectrin/ β-adducin multimeric complexes needed for cytoskeletal stability. The data thus suggest that the PTN-stimulated phosphorylation of serines 713 and 726 in β-adducin disrupts cytoskeletal protein complexes and integrity, features demonstrated in both PTN-stimulated cells and of highly malignant cells that constitutively express the endogenous Ptn gene. The data also support the important conclusion that PTN determines the cellular location of β-adducin phosphorylated in serines 713 and 726 and raise the possibility that β-adducin functions in support of structure of heterochromatin and centrioles during mitosis.