Cell Differentiation Is a Key Determinant of Cathelicidin LL-37/Human Cationic Antimicrobial Protein 18 Expression by Human Colon Epithelium

Abstract

Antimicrobial peptides are highly conserved evolutionarily and are thought to play an important role in innate immunity at intestinal mucosal surfaces. To better understand the role of the antimicrobial peptide human cathelicidin LL-37/human cationic antimicrobial protein 18 (hCAP18) in intestinal mucosal defense, we characterized the regulated expression and production of this peptide by human intestinal epithelium. LL-37/hCAP18 is shown to be expressed within epithelial cells located at the surface and upper crypts of normal human colon. Little or no expression was seen within the deeper colon crypts or within epithelial cells of the small intestine. Paralleling its expression in more differentiated epithelial cells in vivo, LL-37/hCAP18 mRNA and protein expression was upregulated in spontaneously differentiating Caco-2 human colon epithelial cells and in HCA-7 human colon epithelial cells treated with the cell differentiation-inducing agent sodium butyrate. LL-37/hCAP18 expression by colon epithelium does not require commensal bacteria, since LL-37/hCAP18 is produced with a similar expression pattern by epithelial cells in human colon xenografts that lack a luminal microflora. LL-37/hCAP18 mRNA was not upregulated in response to tumor necrosis factor alpha, interleukin 1␣ (IL-1␣), gamma interferon, lipopolysaccharide, or IL-6, nor did the expression patterns and levels of LL-37/hCAP18 in the epithelium of the normal and inflamed colon differ. On the other hand, infection of HCA-7 cells with Salmonella enterica serovar Dublin or enteroinvasive Escherichia coli modestly upregulated LL-37/hCAP18 mRNA expression. We conclude that differentiated human colon epithelium expresses LL-37/ hCAP18 as part of its repertoire of innate defense molecules and that the distribution and regulated expression of LL-37/hCAP18 in the colon differs markedly from that of other enteric antimicrobial peptides, such as defensins.Antimicrobial peptides and proteins play an important role in innate host defense, and this may be particularly important at mucosal surfaces that form the initial barrier between the host and the external environment (3, 18). Cathelicidins are a family of antimicrobial peptides found in many mammalian species (20). The cathelicidins contain a conserved cathelin domain and a C-terminal domain that varies among species, yielding multiple different antimicrobial peptides (22). LL-37 is the only cathelicidin described thus far in humans. Like other cathelicidins, LL-37 is synthesized as a precursor, termed human cationic antimicrobial protein 18 (hCAP18). The precursor is cleaved to the mature peptide LL-37 by a serine protease, protease-3, in neutrophils after exocytosis (45), although it is not known whether the same processing mechanism operates in other cells.LL-37, alone and in synergy with other antimicrobial proteins (e.g., lactoferrin and lysozyme), has a broad range of bactericidal activities against gram-positive and gram-negative bacteria (2,4,47). In addition, LL-37 can bind to and neutralize bacterial...

Cathelicidins in inflammation and tissue repair: Potential therapeutic applications for gastrointestinal disorders

“…For instance, LL-37 is actively produced by surface epithelial cells, as well as chief and parietal cells in the stomach [4] . The expression of LL-37 is also detectable in epithelial cells located at the surface and upper crypts of normal human colon [5] .…”

Bioinformatic discovery and initial characterisation of nine novel antimicrobial peptide genes in the chicken

“…Neutrophils are a particularly rich source of cathelicidins in a variety of species. In humans, cathelicidins have also been found to be expressed in several other tissues, including the testis (Agerberth et al 1995;Malm et al 2000), squamous epithelia (Frohm Nilsson et al 1999;Nizet et al 2001), airway epithelia (Bals et al 1998), sweat glands (Murakami et al 2002b), salivary glands (Murakami et al 2002a) and colon (Hase et al 2002). Cathelicidins have a wide spectrum of antimicrobial activity and have been shown to be active against Gram-negative and Grampositive bacteria (Travis et al 2000), fungi (Shin et al 2000) and enveloped viruses (Tamamura et al 1995).…”

Bacteria in the Intestine, Helpful Residents or Enemies from Within?

“…Cathelicidin LL-37 is expressed within the epithelial cells located at the surface and upper crypts of a normal human colon (47). However, little or no expression was seen within the deeper colon crypts or within epithelial cells of the small intestine (47).…”