Epididymal protein targets: a brief history of the development of epididymal protease inhibitor as a contraceptive.

The Laboratories for Reproductive Biology at the University of North Carolina at Chapel Hill began collaboration with Human Genome Sciences (Rockville MD USA) to sequence a human epididymal library and identify epididymal specific genes. Among the first clones obtained from Human Genome Sciences was a clone for EPPIN (official symbol SPINLW1). Our laboratory has described EPPIN (Epididymal protease inhibitor) as a novel gene on human chromosome 20q12-13.2 which encodes a cysteine-rich protein containing both Kunitz-type and WAP-type four disulfide core consensus sequences that characterize it as a protease inhibitor. EPPIN expresses three mRNA splice variants that encode two protein isoforms found in the testis and epididymis. Of the two isoforms one is secreted and one lacks a secretory signal piece. EPPIN is predominantly a dimer although multiples often exist and in its native form EPPIN is found on the sperm surface complexed with lactotransferrin and clusterin. During ejaculation semenogelin from the seminal vesicles is bound to the EPPIN protein complex initiating a series of events that define EPPINs function: modulating PSA activity providing antimicrobial protection and binding semenogelin thereby inhibiting sperm motility. As PSA hydrolyses semenogelin in the ejaculate coagulum spermatozoa gain progressive motility. Using immunization as a tool to study antigen function we demonstrated that EPPIN is essential for fertility because immunization of male monkeys with recombinant EPPIN results in complete but reversible contraception. To exploit our understanding of EPPINs function we have developed a high throughput screen to look for compounds that inhibit EPPIN-semenogelin interaction and mimic anti-EPPIN inhibiting sperm motility. These compounds are now being developed into a non-hormonal male contraceptive.