– Human PAP, also known as 28 kDa heat- and acid-stable phosphoprotein, PDGF-associated protein, PDGFA-associated protein 1, PDAP1, HASPP28, is a protein which belongs to the PDAP1 family. The encoded protein in rodents has been shown to bind PDGFA with a low affinity. PDGF-Associated Protein (PAP) is a phosphoprotein that may enhance PDGFA-stimulated cell growth in fibroblasts, but inhibits the mitogenic effect of PDGFB. PDAP1 expression is induced by TNF-alpha, and cells overexpressing PDAP1 show significantly less apoptosis on exposure to TNF-alpha.