Insulin-like growth factor II (IGF-II) is a major fetal growth factor. The IGF-II gene generates multiple mRNAs with different 5 untranslated regions (5 UTRs) that are translated in a differential manner during development. We have identified a human family of three IGF-II mRNA-binding proteins (IMPs) that exhibit multiple attachments to the 5 UTR from the translationally regulated IGF-II leader 3 mRNA but are unable to bind to the 5 UTR from the constitutively translated IGF-II leader 4 mRNA. IMPs contain the unique combination of two RNA recognition motifs and four hnRNP K homology domains and are homologous to the Xenopus Vera and chicken zipcode-binding proteins. IMP localizes to subcytoplasmic domains in a growthdependent and cell-specific manner and causes a dose-dependent translational repression of IGF-II leader 3 -luciferase mRNA. Mouse IMPs are produced in a burst at embryonic day 12.5 followed by a decline towards birth, and, similar to IGF-II, IMPs are especially expressed in developing epithelia, muscle, and placenta in both mouse and human embryos. The results imply that cytoplasmic 5 UTR-binding proteins control IGF-II biosynthesis during late mammalian development.Specific RNA-binding proteins are emerging as regulators of cytoplasmic mRNA events such as translatability, stability, and localization. Several examples of these types of regulatory events have been reported in studies of invertebrate embryogenesis and amphibian oogenesis, in which the 3Ј untranslated region (3Ј UTR) has been identified as a repository of regulatory elements (reviewed in reference 35). It is anticipated that similar mechanisms operate during mammalian development, since important physiological roles for RNA-binding proteins have been discerned from deletions of the DAZ and RBM genes leading to azoospermia (9, 26) and from a point mutation in the FMR1 gene resulting in the fragile X mental retardation syndrome (7). RNA-binding proteins often contain one or more RNA-binding motif such as the RNA recognition motif (RRM) and the K homology (KH) domain (reviewed in reference 28), which may either ensure increased specificity towards a single RNA molecule or provide an ability to bind different molecules simultaneously. Moreover, solution structures of the N-terminal RRM domain of the human U1A protein in complex with its own pre-mRNA and of the first KH domain of FMR1 suggest that flexible loop regions provide discriminating binding surfaces for RNA recognition (1, 20).Insulin-like growth factor II (IGF-II) is a fetal growth factor with auto-and paracrine modes of action. In the mouse, lack of IGF-II results in a small but apparently normal progeny (3), whereas an increased IGF-II dose is more detrimental (13, 30). In humans, increased levels of IGF-II are associated with the Beckwith-Wiedemann syndrome, which is characterized by a disproportionate overgrowth of the fetus and malformations (32). IGF-II expression is controlled by parental imprinting, since only the paternal allele is expressed in most tissues (8). However,...

Cathelicidins are a family of antimicrobial proteins found in the peroxidase-negative granules of neutrophils. The known biologic functions reside in the C-terminus, which must be cleaved from the holoprotein to become active. Bovine and porcine cathelicidins are cleaved by elastase from the azurophil granules to yield the active antimicrobial peptides. The aim of this study was to identify the physiological setting for cleavage of the only human cathelicidin, hCAP-18, to liberate the antibacterial and cytotoxic peptide LL-37 and to identify the protease responsible for this cleavage. Immunoelectron microscopy demonstrated that both hCAP-18 and azurophil granule proteins were present in the phagolysosome. Immunoblotting revealed no detectable cleavage of hCAP-18 in cells after phagocytosis. In contrast, hCAP-18 was cleaved to generate LL-37 in exocytosed material. Of the 3 known serine proteases from azurophil granules, proteinase 3 was solely responsible for cleavage of hCAP-18 after exocytosis. This is the first detailed study describing the generation of a human antimicrobial peptide from a promicrobicidal protein, and it demonstrates that the generation of active antimicrobial peptides from common proproteins occurs differently in related species. (Blood. 2001; 97:3951-3959)