Recombinant Human Pref-1/DLK1/FA1 Protein

Human Pref-1 (preadipocyte factor 1), also known as Dlk1 and pG2, belongs to the Notch/Delta/Serrate family of epidermal growth factor (EGF)-like repeat-containing proteins that act as ligands in the Notch signaling pathway (1-4). Human Pref-1 is synthesized as a 383 amino acid (aa) precursor consisting of a 23 aa signal sequence, a 280 aa extracellular region, a 24 aa transmembrane segment, and a 56 aa cytoplasmic tail. The extracellular region contains six tandem EGF-repeats, a juxtamembrane region, and multiple sites for O- and N-glycosylation (3, 5). Heterogeneous transmembrane forms of Pref-1, ranging from 50 to 60 kDa, can be attributed to variability in glycosylation (1-3). In addition to full-length Pref-1A, alternative splicing of the juxtaposition and EGF-repeat regions generate three major short forms, Pref-1B-1D (3, 6). Proteolytic cleavage at one of two extracellular sites in Pref-1A and 1B can produce two soluble forms: a 50 kDa large form and a 24-25 kDa small form (3, 6). Processing of Pref-1C and Pref-1D, by contrast, can produce only small soluble forms. Only the large soluble form demonstrates biological activity (3, 6). Mature human Pref-1A shares 85% aa sequence identity with mouse and rat homologs. Pref-1 is highly expressed in 3T3-L1 preadipocytes and many endocrine tissues, including the growth hormone-producing somatotroph cells of the pituitary gland, insulin-producing ( cells, sex hormone-producing Leydig cells of the testis, and ovarian theca interna and Hilus cells (4). Constitutive expression of Pref-1 in preadipocytes blocks differentiation into mature adipocytes (1-7). Pref-1 also regulates the differentiation of skeletal stem cells, thymocytes, and adrenal gland cells, and inhibits GH secretion in pituitary GH3 cells (4).