Abundant secretory lipocalins displaying male and lactation-specific expression in adult hamster submandibular gland. cDNA cloning and sex hormone-regulated repression.

Abstract

We have previously identified massively expressed 24- and 20.5-kDa male-specific proteins in submandibular salivary glands (SMG) of adult hamsters. Here we report the cloning of the cDNA encoding the 24-kDa protein which we have now found to be a heterogenously N-glycosylated form of the 20.5-kDa protein. The deduced amino acid sequence indicated that the protein is a member of the lipocalin family, the two most related lipocalins being rat odorant-binding protein of nasal mucosa and aphrodisin, a pheromonal protein present in vaginal discharge and saliva of female hamsters. Northern blot analysis showed that cognate mRNA is expressed in hamster SMG and lacrimal gland (LG) displaying marked sex-hormonal repression. The sex-hormonal repression patterns showed similarities and dissimilarities between SMG and LG but they were, respectively, similar to the sex-hormonal repression pattern noted for the SMG 24/20.5-kDa male-specific proteins and for an abundant female-specific 20-kDa LG secretory protein. These SMG and LG proteins were found to be immunologically similar and secretion of the SMG proteins in saliva and their excretion in urine was detected. The male-specific and abundant expression of the SMG proteins were seen at and after sexual maturity but was not dependent on androgens. Surprisingly, a temporary male-like expression of these SMG proteins was seen in lactating females which was obliterated by oestrogen administration. Our results show that despite differences in their repression by sex hormones, the gene for SMG 24/20.5-kDa proteins is similar or identical to that of LG 20-kDa protein and their marked repression by both androgens and oestrogens might be at the transcriptional level. Moreover, they might be excellent models with which to study sex hormone repression of gene expression at the molecular level. The results of homology search and the male- and lactation-specific pressure of the SMG proteins in adult saliva and urine suggests a possibility of their involvement in olfaction-mediated chemical communication between hamsters.