Discovery of new human beta-defensins using a genomics-based approach

Epithelial beta -defensins are broad-spectrum cationic antimicrobial peptid es that also act as chemokines for adaptive immune cells. In the human geno me, all known defensin genes cluster to a <1 Mb region of chromosome 8p22-p 23. To identify new defensin genes, the DNA sequence from a contig of large -insert genomic clones from the region containing human <beta>-defensin-2 ( HBD-2) was analyzed for the presence of defensin genes. This sequence surve y identified a novel beta -defensin, termed HBD-3. The HBD-3 gene contains two exons, is located 13 kb upstream from the HBD-2 gene, and it is transcr ibed in the same direction. A partial HBD-3 cDNA clone was amplified from c DNA derived from IL-1 beta induced fetal lung tissue. The cDNA sequence enc odes for a 67 amino acid peptide that is similar to 43% identical to HBD-2 and shares the beta -defensin six cysteine motif. By PCR analysis of two co mmercial cDNA panels, HBD-3 expression was detected in adult heart, skeleta l muscle, placenta and in fetal thymus. From RT-PCR experiments, HBD-3 expr ession was observed in skin, esophagus, gingival keratinocytes, placenta an d trachea. Furthermore, in fetal lung explants and gingival keratinocytes, HBD-3 mRNA expression was induced by IL-1 beta. Additional sequence analysi s identified the HE2 (human epididymis secretory protein) gene 17 kb upstre am from the HBD-3 gene. One splice variant of this gene (HE2 beta1) encodes a beta -defensin consensus cysteine motif, suggesting it represents a defe nsin gene product. HE2 beta1 mRNA expression was detected in gingival kerat inocytes and bronchial epithelia using RT-PCR analysis. The discovery of th ese novel beta -defensin genes may allow further understanding of the role of defensins in host immunity at mucosal surfaces. (C) 2001 Elsevier Scienc e B.V. All rights reserved.