Identification and expression analysis of an N-terminally truncated isoform of human PDGF-C

Platelet-derived growth factor C (PDGF-C) is a member of the PDGF family that plays an important role in developmental and physiological processes, and in human diseases. Here, we report a novel splice variant of human PDGF-C (PDGF-Cb), which encodes an N-terminally truncated protein, lacking the signal peptide and CUB domain. This variant is coexpressed with PDGF-C in all normal tissues analyzed. PDGF-Cb is produced as a cytoplasmic protein, and has a similar intracellular localization to PDGF-C, but is not secreted from transfected cells. Further, we show that PDGF-Cb can form heterodimers (PDGF-CCb) with PDGF-C, which is thereby retained and degraded within cells. In primary renal cell carcinoma (RCC), expression of the two alternatively spliced transcripts was different. Generally, expression of the full-length PDGF-C transcript was increased in RCC tumors, whereas expression of PDGF-Cb was not in the 30 analyzed cases with paired RCC tumor tissues and normal renal tissues. Based on these findings, we suggest that PDGF-Cb might act as a dominant negative molecule regulating the secretion of PDGF-C, and that deregulation of full-length PDGF-C is involved in RCC tumorigenesis.