The growth factor progranulin (PGRN) regulates cell division, survival, and migration. PGRN is an extracellular glycoprotein bearing multiple copies of the cysteine-rich granulin motif. With PGRN family members in plants and slime mold, it represents one of the most ancient of the extracellular regulatory proteins still extant in modern animals. PRGN has multiple biological roles. It contributes to the regulation of early embryogenesis, to adult tissue repair and inflammation. Elevated PGRN levels often occur in cancers, and PGRN immunotherapy inhibits the growth of hepatic cancer xenografts in mice. Recent studies have demonstrated roles for PGRN in neurobiology. An autosomal dominant mutation in GRN, the gene for PGRN, leads to neuronal atrophy in the frontal and temporal lobes, resulting in the disease frontotemporal lobar dementia. In this review we will discuss current knowledge of the multifaceted biology of PGRN.

Progranulin is a secreted protein with important functions in several physiological and pathological processes, such as embryonic development, host defense, and wound repair. Autosomal dominant mutations in the progranulin gene cause frontotemporal dementia, while overexpression of progranulin promotes the invasive progression of a range of tumors, including those of the breast and the brain. Structurally, progranulin consists of seven-and-a-half tandem repeats of the granulin/epithelin module (GEM), several of which have been isolated as discrete 6-kDa GEM peptides. We have expressed all seven human GEMs using recombinant DNA in Escherichia coli. High-resolution NMR showed that only the three GEMs, hGrnA, hGrnC, and hGrnF, contain relatively well-defined three-dimensional structures in solution, while others are mainly mixtures of poorly structured disulfide isomers. The three-dimensional structures of hGrnA, hGrnC, and hGrnF contain a stable stack of two b-hairpins in their N-terminal subdomains, but showed a more flexible C-terminal subdomain. Interestingly, of the well-structured GEMs, hGrnA demonstrated potent growth inhibition of a breast cancer cell line, while hGrnF was stimulatory. Poorly folded peptides were either weakly inhibitory or without activity. The functionally active and structurally well-characterized human hGrnA offers a unique opportunity for detailed structure-function studies of these important GEM proteins as novel members of mammalian growth factors.Keywords: granulin/epithelin module; progranulin; NMR; structure; functional activity Abbreviations: PGRN, progranulin, also called the granulin/epithelin precursor or GEP; GEM, granulin/epithelin-like module; hGrnX, human granulin X, where X is A, B, C, D, E, F, G, or P; cGrn1, carp granulin-1; S2H, stack of two b-hairpins; S4H, stack of four b-hairpins; CDAP, 1-cyano-4-dimethylamino-pyridinium tetrafluoroborate; TCEP, tris(2-carboxyethyl)phosphine; itz, 2-iminothiazolidine-4-carboxyl, resulting from the aqueous ammonia cleavage of a peptide on the Nterminal side of the S-cyanylated cysteines; hGrnA-itz-a-b-red, a fully reduced fragment of hGrnA obtained after CN-induced cleavage before cysteines in positions a and (b + 1); hGrnA-(-2)-a-red, a fully reduced N-terminal fragment of hGrnA obtained after CN-induced cleavage before cysteine in position (a + 1); m/z, mass to charge ratio; TFA, trifluoroacetic acid.Article and publication are at