Major Role of Human KLK14 in Seminal Clot Liquefaction

Abstract

Liquefaction of human semen involves proteolytic degradation of the seminal coagulum and release of motile spermatozoa. Several members of human kallikrein-related peptidases (KLKs) have been implicated in semen liquefaction, functioning through highly regulated proteolytic cascades. Among these, KLK3 (also known as prostate-specific antigen) is the main executor enzyme responsible for processing of the primary components of semen coagulum, semenogelins I and II. We have recently identified KLK14 as a potential activator of KLK3 and other KLKs. This study aims to elucidate the cascade-mediated role of KLK14 ex vivo. KLK14 expression was significantly lower (p ‫؍‬ 0.0252) in individuals with clinically delayed liquefaction. Concordantly, KLK14 expression was significantly (p ‫؍‬ 0.0478) lower in asthenospermic cases. Specific inhibition of KLK14 activity by the synthetic inhibitor ACT G9 resulted in a significant delay in semen liquefaction, a drop in the "early" (30 min postejaculation) "chymotrypsin-like" and KLK1 activity, and an increase in the "late" (90 min postejaculation) chymotrypsinlike activity. Conversely, the addition of recombinant active KLK14 facilitated the liquefaction process, augmented the early chymotrypsin-like activity, and lowered late chymotrypsin-like activity. Given that the observed chymotrypsin-like activity was almost completely attributed to KLK3 activity, KLK3 seems to be regulated bidirectionally. Accordingly, a higher level of KLK3 fragmentation was observed in KLK14-induced coagula, suggesting an inactivation mechanism via internal cleavage. Finally, semenogelins I and II were directly cleaved by KLK14. Semenogelins were also able to reverse KLK14 inhibition by Zn 2؉ , providing a novel regulatory mechanism for KLK14 activity. Our results show that KLK14 exerts a significant and dose-dependent effect in the process of semen liquefaction.

Unleashing the therapeutic potential of human kallikrein-related serine proteases

“…KLK3 expression is restricted to the prostate and hence it is also known as the prostate-specific antigen (PSA). In normal prostate physiology, KLK3 cleaves fibronectin and the seminal-gel-forming proteins semenogelin 1 and semenogelin 2, leading to semen liquefaction and enhanced sperm motility [109][110][111][112][113] (FIG. 3a).…”

Liquefaction of Semen Generates and Later Degrades a Conserved Semenogelin Peptide That Enhances HIV Infection

“…S3 in the supplemental material) and is therefore unlikely to be the primary SEM1(86-107)-cleaving protease. Given that degradation of SEM1(86-107) in semen is inhibited in the presence of a serine protease inhibitor, it is likely that the responsible protease(s) is another serine protease(s), such as the numerous kallikrein-related peptidases expressed in human semen (28)(29)(30).…”

Sunflower trypsin inhibitor (SFTI-1) analogues of synthetic and biological origin via N→S acyl transfer: potential inhibitors of human Kallikrein-5 (KLK5)

“…12 SFTI-1 is known to act upon a range of serine proteases, including cathepsin G7, matriptase, 13 and kallikrein-related peptidases (KLKs), 14 a group of fifteen related human proteases with roles in a variety of physiological processes and strong links to cancer progression. 15,16 Swedberg and co-workers recently observed inhibition of KLK4, a promising target for prostate cancer treatment, by SFTI-1. 14 They produced a sequence variant (where RCTK was modified to FCQR) with increased potency and improved selectivity over other proteases.…”