The mouse Vcs2 gene is a composite structure which evolved by gene fusion and encodes five distinct salivary mRNA species

The PBII gene of the human salivary proline-rich protein P-B produces another protein, Q504X8, with an opiorphin homolog, QRGPR

OBJECTIVES

The NCBI gene database and human-transcriptome database for alternative splicing were used to determine the expression of mRNAs for P-B (SMR3B) and variant form of P-B. The translational product from the former mRNA was identified as the protein named P-B, whereas that from the latter has not yet been elucidated. In the present study, we investigated the expression of P-B and its variant form at the protein level.

DESIGN

To identify the variant protein of P-B, (1) cationic proteins with a higher isoelectric point in human pooled whole saliva were purified by a two dimensional liquid chromatography; (2) the peptide fragments generated from the in-solution of all proteins digested with trypsin separated and analyzed by MALDI-TOF-MS; and (3) the presence or absence of P-B in individual saliva was examined by 15% SDS-PAGE.

RESULTS

The peptide sequences (I³⁷PPPYSCTPNMNNCSR⁵², C⁵³HHHHKRHHYPCNYCFCYPK⁷², R⁵⁹HHYPCNYCFCYPK⁷² and H⁶⁰HYPCNYCFCYPK⁷²) present in the variant protein of P-B were identified. The peptide sequence (G⁶PYPPGPLAPPQPFGPGFVPPPPPPPYGPGR³⁶) in P-B (or the variant) and sequence (I³⁷PPPPPAPYGPGIFPPPPPQP⁵⁷) in P-B were identified. The sum of the sequences identified indicated a 91.23% sequence identity for P-B and 79.76% for the variant. There were cases in which P-B existed in individual saliva, but there were cases in which it did not exist in individual saliva.

CONCLUSIONS

The variant protein is produced by excising a non-canonical intron (CC-AC pair) from the 3'-noncoding sequence of the PBII gene. Both P-B and the variant are subject to proteolysis in the oral cavity.

Androgen inducibility ofFgf8 in Shionogi carcinoma 115 cells correlates with an adjacent t(5;19) translocation

Fgf8 (fibroblast growth factor 8) was initially cloned from a mouse mammary tumor cell line derived from the androgen-dependent Shionogi carcinoma 115. The androgen-inducible expression of Fgf8 in this tumor controls its androgen-dependent phenotype, thus stimulating interest in this gene as a possible factor in human prostate cancer and other androgen-sensitive cancers. However, apart from Shionogi carcinoma 115, the androgen inducibility of Fgf8 is controversial. In the present study, having not detected androgen-inducible expression of Fgf8 in other mouse mammary cell lines or mouse prostate, we examined the Shionogi carcinoma 115-derived S115 cell line for mouse mammary tumor virus (MMTV) insertions or other nearby DNA rearrangements that might explain the androgen inducibility of Fgf8 in these cells. Southern blotting did not detect MMTV insertions near Fgf8 but did reveal a specific DNA rearrangement 3.7 kb upstream of Fgf8 in S115 cells and in other cells (SC115) independently derived from Shionogi carcinoma 115. Spectral karyotyping of S115 cells and sequencing of the cloned rearrangement junctions indicate that Fgf8 is involved in a t(5;19) translocation. The chromosome 5 sequence joined to Fgf8 is immediately adjacent to Smr2 (submaxillary gland androgen-regulated protein 2) and includes Muc10 (mucin 10), two genes that we show are testosterone inducible in S115 cells, suggesting that the androgen-dependent expression of Fgf8 in Shionogi carcinoma 115 and derivative cells results from this translocation. Together, these results suggest that androgen inducibility is not an inherent property of the Fgf8 gene, which has implications regarding this gene's proposed role in the etiology of hormone-responsive cancers.

Acinar cells are target cells for androgens in mouse submandibular glands

The variable coding sequence (VCS) multigene family encodes diverse salivary proteins, such as the SMR1 prohormone and the PR-VB1 proline-rich protein in the rat. In situ hybridization was used to study the cell-specific expression of two new mouse VCS genes, Vcs1 and Vcs2. We show that the Vcs1 transcripts, which code for a proline-rich protein, MSG1, are highly abundant in male and female parotid glands, in which they are specifically detected in acinar cells. No expression was seen in the submandibular or sublingual glands. In contrast, Vcs2 transcripts were found only in the acinar cells of the submandibular glands (SMGs) of male mice, in which they are expressed in response to androgens. Expression was found to be heterogeneous within acinar structures. No Vcs2 transcripts were detected in the SMGs of females or castrated males by Northern blot, RNase protection, or in situ hybridization. Androgen administration to females or castrated males induced expression at a level comparable to that of intact males. The Vcs2 gene is the first example of a mouse androgen-regulated gene that is expressed in SMG acinar cells. This result, in addition to our previous observation on SMR1 expression in rats, demonstrates that both acinar cells and granular convoluted tubule (GCT) cells are target cells for androgen action in rodent SMG.