CDNA CLONING OF AN ABUNDANT HUMAN LACRIMAL GLAND MESSENGER-RNA ENCODING A NOVEL TEAR PROTEIN

An abundant 1.05 kb human lacrimal gland mRNA has been characterized b y cDNA cloning. It encodes a predicted 180 residue, 20546 Da secreted protein, with a charge of +11 at pH 7 and 24.5% proline, designated as Basic Proline-rich Lacrimal Protein (BPLP). Southern blot analysis is consistent with a single BPLP gene. BPLP lacks any distinct repetitiv e structure, and is unrelated to the salivary proline-rich protein sup er family. The pre-proprotein shows modest overall similarity to a sup erfamily comprising human PRPb, the mouse MSG proteins, and rat VCS-al pha 1, VCS-beta 1 and submandibular apomucin. BPLP also contains a dom ain with similarity to the Zp2 protein domain found in several otherwi se unrelated proteins. Northern blot analysis indicated that the BPLP gene is also expressed at modest levels in the human submandibular gla nd, and in situ hybridization demonstrated expression of BPLP in the s ecretory end-pieces of the human lacrimal gland. The BPLP cDNA clone d efines a new human tear protein, and should provide a useful phenotypi c marker of differentiation in in vitro studies of lacrimal gland func tion.