Platelet-derived growth factor (PDGF) is a broadly expressed mitogenic and
chemotactic factor with diverse roles in a number of physiologic and pathol
ogic settings. The zinc finger transcription factors Sp1, Sp3 and Egr-1 bin
d to overlapping elements in the proximal PDGF B-chain promoter and activat
e transcription of this gene. The anthracycline nogalamycin has previously
been reported to inhibit the capacity of Egr-1 to bind DNA in vitro. Here w
e used electrophoretic mobility shift assays to show that nogalamycin added
to cells in culture did not after the interaction of Egr-1 with the PDGF-B
promoter. Instead, it enhanced the capacity of Sp1 to bind DNA, Nogalamyci
n increased PDGF-8 mRNA expression at the level of transcription, which was
abrogated by mutation of the Sp1 binding site in the PDGF-B promoter or ov
erexpression of mutant Sp1, Rather than increasing total levels of Sp1, nog
alamycin altered the phosphorylation state of the transcription factor. Ove
rexpression of dominant-negative PKC-zeta blocked nogalamycin-inducible Sp1
phosphorylation and PDGF-B promoter-dependent expression, Nogalamycin stim
ulated the phosphorylation of PKC-zeta (on residue Thr(410)). These finding
s demonstrate for the first time that PKC-zeta and Spl phosphorylation medi
ate the inducible expression of this growth factor.