Identification of a cell retention signal in the B-chain of platelet-derived growth factor and in the long splice version of the A-chain.
The B-chain homodimer of platelet-derived growth factor (PDGF) is only very inefficiently secreted and remains largely associated with the producer cell; in contrast, the dimer of the short, and most common, splice variant of the A-chain is secreted. To identify the structural background to the differences in the secretory pattern between the different isoforms of PDGF, a set of chimeric PDGF A/B cDNAs was generated and expressed in COS cells. Analyses of the biosynthesis and processing of the corresponding products led to the identification of a determinant for cell association in the carboxy-terminal third of the PDGF B-chain precursor. Introduction of stop codons at various positions in the carboxy-terminal prosequence of the PDGF B-chain localized this determinant to an 11-amino-acid-long region (amino acids 219-229). This region contains an 8-amino-acid-long basic sequence that is homologous to a sequence present in an alternatively spliced longer version of the PDGF A-chain. In contrast to the short splice variant, the long splice A-chain version, like the B-chain, was found to remain predominantly cell associated. Thus, we have identified a conserved sequence that inhibits the secretion of some of the PDGF isoforms. Our data also suggest that switching of splicing patterns can be a mechanism to regulate the formation of secreted or cell-associated forms of PDGF-AA and possibly other growth factors.
Ostman
A
A
Ludwig Institute for Cancer Research, Biomedical Center, Uppsala, Sweden.
Andersson
M
M
Betsholtz
C
C
Westermark
B
B
Heldin
C H
CH
D000595:Amino Acid Sequence; D000818:Animals; D002451:Cell Compartmentation; D002460:Cell Line; D005822:Genetic Vectors; D008969:Molecular Sequence Data; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D010982:Platelet-Derived Growth Factor / Q000737:chemistry* / Q000378:metabolism; D021382:Protein Sorting Signals / Q000032:analysis*
D010982:Platelet-Derived Growth Factor; D021382:Protein Sorting Signals