C120RF39, a novel secreted protein with a typical amidation processing signal

In the present study we describe a novel secreted protein, named C120RF39 (chromosome 12 open-reading framework 39), which contains a typical amidation/proteolytic processing signal (Gly-Arg-Arg motif). Interestingly, C120RF39 protein is not hydrolysed, but is a full-length protein without signal peptides. Western blotting indicated that c-Myc-tagged C120RF39 is secreted into culture medium in transfected HeLa cells. Quantitative RT-PCR (reverse transcription-PCR) analysis revealed that c12orf39 is mainly expressed in placenta and brain. Immunohistochemistry on formalin-fixed paraffin-embedded human term placenta using a rabbit antibody against human C120RF39 demonstrated that the protein was localized extracellularly, surrounding the trophoblastic cells. In addition, C120RF39 secretion could be blocked by brefeldin A, suggesting that the secretion of C120RF39 is dependent on the Golgi apparatus. Furthermore, laser-scanning confocal microscopy also confirmed that the C120RF39 protein co-localized with the Golgi apparatus. Taken together, although C120RF39 is not a secreted small peptide, it can also be secreted to play a role in the biological functions of the placenta.