The Ubiquitin-Proteasome System Does Not Regulate the Degradation of Porcine β-Microseminoprotein during Sperm Capacitation

Abstract

Sperm capacitation, one of the key events during successful fertilization, is associated with extensive structural and functional sperm remodeling, beginning with the modification of protein composition within the sperm plasma membrane. The ubiquitin-proteasome system (UPS), a multiprotein complex responsible for protein degradation and turnover, participates in capacitation events. Previous studies showed that capacitation-induced shedding of the seminal plasma proteins such as SPINK2, AQN1, and DQH from the sperm surface is regulated by UPS. Alterations in the sperm surface protein composition also relate to the porcine β-microseminoprotein (MSMB/PSP94), seminal plasma protein known as immunoglobulin-binding factor, and motility inhibitor. MSMB was detected in the acrosomal region as well as the flagellum of ejaculated boar spermatozoa, while the signal disappeared from the acrosomal region after in vitro capacitation (IVC). The involvement of UPS in the MSMB degradation during sperm IVC was studied using proteasomal interference and ubiquitin-activating enzyme (E1) inhibiting conditions by image-based flow cytometry and Western blot detection. Our results showed no accumulation of porcine MSMB either under proteasomal inhibition or under E1 inhibiting conditions. In addition, the immunoprecipitation study did not detect any ubiquitination of sperm MSMB nor was MSMB detected in the affinity-purified fraction containing ubiquitinated sperm proteins. Based on our results, we conclude that UPS does not appear to be the regulatory mechanism in the case of MSMB and opening new questions for further studies. Thus, the capacitation-induced processing of seminal plasma proteins on the sperm surface may be more complex than previously thought, employing multiple proteolytic systems in a non-redundant manner.

Kojic acid inhibits pig sperm apoptosis and improves capacitated sperm state during liquid preservation at 17°C

“…During sperm capacitation, there are continuous physiological changes that remodel the structure of the sperm and alter the composition of proteins in the sperm plasma membrane, such as the ubiquitin‐proteasome system (UPS) plays a crucial part in the removal of sperm surface proteins and the plasma membrane remodeling during sperm capacitation (Tumova et al, 2020). Sperm integrity and functional activity are closely linked to sperm capacitation, acrosome reaction, motility, and binding ability with zona pellucida and yolk membrane.…”

TMT-Based Comparative Proteomic Analysis of the Spermatozoa of Buck (Capra hircus) and Ram (Ovis aries)

“…Studies using mammalian sperm have uncovered information on the action of the ubiquitin-proteasome system (UPS) in the modulation of fertilization, involving sperm interactions with ZP, as well as early stages of sperm acquisition, the remodelling of the sperm plasma membrane and apical body, and the gain in sperm fertilization capacity [26,27]. Differentially abundant proteins of this study were enriched in the proteasome pathway: PSMA3 (proteasome subunit α type-3), PSMA7 (proteasome subunit α type-7), PSMA8 (proteasome subunit alpha4s), PSMC2 (proteasome 26S subunit ATPase 2), PSMD3 (26S proteasome non-ATPase regulatory subunit 3), PSMD4 (26S proteasome non-ATPase regulatory subunit 4), PSMD11 (26S proteasome non-ATPase regulatory subunit 11) and PSMD14 (26S proteasome non-ATPase regulatory subunit 14).…”

Mysteries and unsolved problems of mammalian fertilization and related topics

“…Tyrosine phosphorylation of sperm proteins believed to be an essential component of capacitation takes place in the plasma membrane covering the acrosome of sperm head as well as the fibrous sheath, dense fibers, and axoneme in the principal piece of sperm tail where the Ca 2+ channel protein CatSper is localized [ 80 , 88 , 89 ]. The ubiquitin-proteasome system, which plays critical roles in sperm acrosome reactions and sperm-oocyte interactions [ 90 ], may not be involved directly in sperm capacitation [ 91 ]. It is rather astonishing that sperm capacitation, discovered 70 years ago [ 2–4 ], still remains a bit of a mystery today.…”