Identification and cDNA cloning of headpin, a novel differentially expressed serpin that maps to chromosome 18q

Differential display was used to identify a novel serpin (headpin) underexpressed in squamous cell cancers of the oral cavity. Headpin cDNA encoding a complete open reading frame was cloned and sequenced. Headpin is expressed in normal oral mucosal tissue, skin, and cultured keratinocytes. Using Northern analysis and relative reverse-transcription polymerase chain reaction (relative RT-PCR), downregulation of headpin mRNA expression was demonstrated in oral cavity squamous carcinomas. Northern blot analysis identified a 3. 3-kb headpin mRNA transcript. Headpin is a 391-amino-acid protein with a theoretical molecular weight of 44 kDa. Hinge region homology at the reactive site loop suggests that headpin belongs to the inhibitory class of serine protease inhibitors. Headpin was mapped to 18q21.3/18q22. This region includes the ovalbumin serpins (ov-serpins) maspin, SCCA1, SCCA2, and PAI-2. Furthermore, 18q is recognized as a region for frequent loss of heterozygosity (LOH) in head and neck cancer and other malignancies.