Identification of CRISP2 from human sperm as PSP94-binding protein and generation of CRISP2-specific anti-peptide antibodies

CAP superfamily proteins in human: a new target for cancer therapy

The CAP (Cysteine-rich secretory protein, Antigen 5, and Pathogenesis-related protein 1) superfamily proteins (CAP proteins) are found in all kingdoms of life. The cysteine-rich secreted proteins are prevalent in human organs and tissues and serve as critical signaling molecules within cells, regulating a wide range of biochemical processes in the human body. Due to their involvement in numerous biological processes, CAP proteins have recently attracted significant attention, particularly in the context of tumorigenesis and cancer therapy. This review summarizes the expression patterns and roles of CAP proteins in various cancers. Additionally, it analyzes the mechanisms by which CAP proteins affect cancer cell proliferation and survival, regulate epithelial-mesenchymal transition, influence drug resistance, and regulate epigenetics. The review reveals that CAP proteins play distinct roles in various signaling pathways, such as the MAPK, PI3K-Akt, and p53 pathways, which are crucial for tumor progression. Furthermore, this review summarizes the tumor-inhibiting function of CAP proteins and their potential as cancer biomarkers. These findings suggest that CAP proteins represent a promising new target for innovative cancer diagnosis and treatment.

Prostate secretory protein 94 (PSP94) inhibits sterol-binding and export by the mammalian CAP protein CRISP2 in a calcium-sensitive manner

Members of the CAP protein superfamily are present in all kingdoms of life and have been implicated in many different processes, including pathogen defense, immune evasion, sperm maturation, and cancer progression. Most CAP proteins are secreted glycoproteins and share a unique conserved αβα sandwich fold. The precise mode of action of this class of proteins, however, has remained elusive. Saccharomyces cerevisiae has three CAP family members, termed pathogen related in yeast (Pry). We have previously shown that Pry1 and Pry2 export sterols in vivo and that they bind sterols in vitro. This sterol binding and export function of yeast Pry proteins is conserved in the mammalian CRISP proteins and other CAP superfamily members. CRISP3 is an abundant protein of the human seminal plasma and interacts with prostate secretory protein of 94 amino acids (PSP94), another major protein component in the seminal plasma. Here we examine whether the interaction between CRISP proteins and PSP94 affects the sterol binding function of CAP family members. We show that coexpression of PSP94 with CAP proteins in yeast abolished their sterol export function and the interaction between PSP94 and CAP proteins inhibits sterol binding in vitro. In addition, mutations that affect the formation of the PSP94–CRISP2 heteromeric complex restore sterol binding. Of interest, we found the interaction of PSP94 with CRISP2 is sensitive to high calcium concentrations. The observation that PSP94 modulates the sterol binding function of CRISP2 in a calcium-dependent manner has potential implications for the role of PSP94 and CRISP2 in prostate physiology and progression of prostate cancer.

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

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.

Purification and characterization of CRISP-3 from human seminal plasma and its real-time binding kinetics with PSP94

Cysteine-rich secretory proteins (CRISPs) have been postulated to have a role in male reproduction and prostate pathophysiology. Of the mammalian CRISPs, CRISP-3 levels in particular have been shown to be upregulated in prostate cancer. Efforts have been made to obtain highly pure CRISP-3 for gaining structure-function information of this protein. However, well characterized and highly pure protein is not available yet. CRISPs from snake venom have been purified using prostate secretory protein of 94 amino acids (PSP94) has been reported earlier. In the present study, CRISP-3 was purified to homogeneity from human seminal plasma using human PSP94-immnobilized affinity column. The molecular mass of the purified protein was determined by SDS-PAGE followed by immunoblotting and found to be ∼26kDa and ∼28kDa. The purity was further verified using MALDI-TOF MS analysis, where two peaks at m/z 25509 and 27715 were obtained. The lower molecular weight peak corresponds to the calculated molecular mass of CRISP-3 (∼26kDa); whereas the higher molecular weight peak was confirmed to be the glycosylated form (∼28kDa) from the deglycosylation experiment. Binding of PSP94 in increasing concentrations to purified CRISP-3 immobilized chip was further validated using surface plasmon resonance. The kinetics data suggested that purified CRISP-3 binds specifically and with high affinity to PSP94. In conclusion, a homogeneous preparation of highly pure CRISP-3 protein is obtained from human seminal plasma.