Mitochondrial localization of CNP2 is regulated by phosphorylation of the N-terminal targeting signal by PKC: implications of a mitochondrial function for CNP2 in glial and non-glial cells.

Both 2',3'-cyclic nucleotide-3'-phosphodiesterase (CNP) isoforms are abundantly expressed in myelinating cells. CNP2 differs from CNP1 by a 20 amino acid N-terminal extension and is also expressed at much lower levels in non-myelinating tissues. The functional role of CNP2, apart from CNP1, and the significance for CNP2 expression in non-myelinating tissues are unknown. Here, we demonstrate that CNP2 is translocated to mitochondria by virtue of a mitochondrial targeting signal at the N-terminus. PKC-mediated phosphorylation of the targeting signal inhibits CNP2 translocation to mitochondria, thus retaining it in the cytoplasm. CNP2 is imported into mitochondria and the targeting signal cleaved, yielding a mature, truncated form similar in size to CNP1. CNP2 is entirely processed in adult liver and embryonic brain, indicating that it is localized specifically to mitochondria in non-myelinating cells. Our results point to a broader biological role for CNP2 in mitochondria that is likely to be different from its specific role in the cytoplasm, along with CNP1, during myelination.