Identification of prostatic-secreted proteins in mice by mass spectrometric analysis and evaluation of lobe-specific and androgen-dependent mRNA expression

Rats and guinea pigs have frequently been used to study the development of the prostate and the mechanism of androgen action, but the mouse prostate has also become an attractive model for prostate research, because an enormous range of genetically altered mice is now available. However, the secretion of proteins in the mouse prostate has not yet been thoroughly investigated. In the present study, major secreted proteins from the ventral prostate (VP), dorsolateral prostate (DLP), and anterior prostate (AP) of mice were identified by means of 2D-gel electrophoresis followed by MALDI-TOF mass spectrometric analysis. A quantitative reverse transcriptase-PCR method was further employed to examine the androgen-dependent transcriptional regulation of the identified proteins. Proteome analysis revealed that the VP secretes spermine-binding protein, serine protease inhibitor Kazal type-3, and a 91 kDa hypothetical scavenger receptor (AK035662). DLP and AP secrete a protein similar to immunoglobulin-binding protein, immunoglobulin-binding protein-like protein, and one of the experimental autoimmune prostatitis antigen proteins (EAPA2). Peroxiredoxin-6, glucose-regulated protein 78, zinc-alpha 2-glycoprotein, and phospholipase C alpha are also secreted. Castration of animals led to a decrease in the mRNAs of these secreted proteins, although the extents of changes varied greatly among different lobes. We present here an outlined view of mouse prostate secretion, which should con tribute to an understanding of the biological functions of the prostate gland, as well as the androgen dependency of prostate secretion.