SERPINF1 and neoplasm: The molecular mechanisms by which PEDF mediates tumor cell differentiation to a less malignant phenotype and protects normal neuronal cells likely involve a very complex system of regulation because the PEDF gene, which harbors a typical signal-peptide sequence, initiator methionine codon, and polyadenylation signal, and fits the size of the other members of the serpin superfamily (e.g., a1pha 1 anti-trypsin), is not homologous at the putative serpin reactive center [37].