A major human lacrimal gland mRNA encodes a new proline-rich protein family member.

PURPOSE

To examine the existence of novel protein products of the human lacrimal gland.

METHODS

cDNA clones corresponding to a highly abundant human lacrimal gland mRNA were isolated and sequenced. Tissue distribution of expression was studied by Northern blot analysis, RNase protection analysis, and in situ hybridization.

RESULTS

A highly abundant 600-base mRNA was identified, and corresponding cDNA clones were isolated. The mRNA has a 134-residue open reading frame encoding a secreted protein of 13458 Da. This protein shows 45.5% similarity to human salivary acidic proline-rich protein PRP 1 and has a similar domain structure, but, unlike other members of the proline-rich protein family, it lacks a conserved repetitive domain. The lacrimal proline-rich protein is encoded by a single gene, designated as LPRP. Expression of LPRP was also detected in the human submandibular, von Ebners, sublingual, and parotid glands. LPRP was expressed in the acinar cells of the lacrimal gland, and in the submandibular gland expression of the LPRP and PRP 1 genes was localized to the serous acini and demilunes.

CONCLUSIONS

The human lacrimal gland produces a previously unknown member of the proline-rich protein family. By analogy with other proline-rich proteins, this LPRP most likely mediates protective functions in the eye, such as modulation of the microflora. In contrast to other proline-rich protein genes, LPRP is expressed in the lacrimal acinar cells, and other anterior exocrine glands. LPRP should be a useful marker for human lacrimal gland acinar cell function in vitro.