Cav-p60, a specific and ubiquitous caveolar protein, was immunoprecipitated from solubilized rat adipocyte plasma membranes and identified as similar to a GeneBank entry annotated mouse polymerase transcript release factor (PTRF) by MALDI-TOF and MS-MS of major fragments. Cloning and virtual translation of the corresponding rat adipocyte cDNA sequence revealed 98.7% identity with mouse PTRF. In vitro translation of this sequence produced a protein, which was recognized by antibodies to both cav-p60 and PTRF. EM gold labeling studies showed that a rabbit antiserum against murine PTRF immunolabeled caveolae specifically in adipocytes from both mouse and rat. In view of the reported function of the protein, which is exerted in the cell nucleus, its subcellular localization was investigated. We found that the protein could be purified by differential solubilization of a plasma membrane fraction followed by SDS-PAGE, and that the protein was as abundant as caveolin in this fraction. We were unable to detect the protein in cell nuclei by subcellular fractionation or fluorescence microscopy. The results show that in a large number of cell types, PTRF is essentially located to caveolae, and that each caveola harbors many copies of the protein. Consequently, we suggest the name Cavin for this protein.

The human cathelicidin, hCAP-18, is expressed both in neutrophils and in epithelial cells. hCAP-18 is processed to the antimicrobial peptide LL-37 by proteinase 3 in neutrophils. hCAP-18 is highly expressed in the epididymis with a subsequent high concentration in seminal plasma where the protein is present in its unprocessed and antimicrobially inactive form. We report here that hCAP-18 in seminal plasma is processed to generate a 38-amino acid antimicrobial peptide ALL-38 by the prostate-derived protease gastricsin when incubated at a pH corresponding to the vaginal pH. In accordance with this, seminal plasma derived hCAP-18 was found in its processed form in the vagina following sexual intercourse. The antimicrobial activity of ALL-38 against a variety of microorganisms tested is equal to that of LL-37. This enzymatic activation of a proantimicrobial substance in seminal plasma following exposure to the vaginal milieu represents a novel mechanism to prevent infection following sexual intercourse.Antimicrobial peptides are important effector molecules of the innate immune system from insects to humans (1, 2). The peptides are active against a broad spectrum of Gram-positive and Gram-negative bacteria as well as some fungi and enveloped viruses. These peptides may play a role in the regulation of the normal microflora (3). In mammals, the antimicrobial peptides are of major importance for the antimicrobial efficacy of professional phagocytes such as neutrophils and macrophages, but the peptides are also expressed in epithelial cells (4). In mammals, there are two large families of antimicrobial peptides, defensins and cathelicidins. Defensins are divided into the ␣-defensins found in neutrophils, macrophages, and Paneth cells in the small intestine, and the ␤-defensins, which are found widespread in epithelial cells. Cathelicidins are found mainly in neutrophils (5). Members of this protein family share a highly conserved N terminus of 12 kDa, named cathelin after a protein isolated from porcine neutrophils (6).Antimicrobial peptides are synthesized as preproproteins and (with the exception of defensins in neutrophils) stored as inactive proproteins (7). In order to become biologically active, the peptides must be liberated from the proproteins by proteolytic cleavage.The proteolytic generation of antimicrobial peptides is very important for the clearance of bacteria at sites of infection. In mice, ␣-defensins from Paneth cells in the small intestine are generated by matrilysin-mediated cleavage of prodefensins, and matrilysin knock-out mice have increased susceptibility to intestinal infections (8). Inhibition of activation of the porcine neutrophil cathelicidins by elastase impairs clearance of bacteria from wounds in vivo (9).The only human cathelicidin, hCAP-18, is a major protein of the specific granules of human neutrophils (10). It is processed to the antimicrobial peptide LL-37 by extracellular cleavage by proteinase 3 from azurophil granules following exocytosis (11). LL-37 has broad spectrum antimicro...