Construction and analysis of a human testis/sperm-enriched interaction network: Unraveling the PPP1CC2 interactome.

BACKGROUND: Phosphoprotein phosphatase 1 catalytic subunit gamma 2 (PPP1CC2), a PPP1CC tissue-specific alternative splice restricted to testicular germ cells and spermatozoa, is essential for spermatogenesis and spermatozoa motility. The key to understand PPP1CC2 regulation lies on the characterization of its interacting partners. METHODS: We construct a testis/sperm-enriched protein interaction network and analyzed the topological properties and biological context of the network. Further the interaction of a potential target for pharmacological intervention was validated in human spermatozoa. RESULTS: A total of 1778 proteins and 32,187 interactions between them were identified in the testis/sperm-enriched network. The network analysis revealed the members of functional modules that interact more tightly with each other. In the network, PPP1CC was located in the fourth maximum core part (k=41) and had 106 direct interactors. Sixteen PPP1CC interactors were involved in spermatogenesis-related categories. Also, PPP1CC had 50 direct interactors, highly interconnected and many of them part of the network maximum core (k=44), associated with motility-related annotations, including several previously uncharacterized interactors, such as, LMNA, JAK2 and RIPK3. CONCLUSIONS: In this study we integrated tissue-specific protein expression and protein-protein interaction data in order to identify key PPP1CC2 complexes for male reproductive functions. One of the most intriguing interactors was A-kinase anchor protein 4 (AKAP4), a testis-specific protein related to infertility phenotypes and involved in all major motility-related annotations. GENERAL SIGNIFICANCE: We demonstrated for the first time the interaction between PPP1CC2 and AKAP4 in human spermatozoa and the potential of the complex as contraceptive target.

Amyloid precursor protein interaction network in human testis: sentinel proteins for male reproduction.

BACKGROUND: Amyloid precursor protein (APP) is widely recognized for playing a central role in Alzheimer's disease pathogenesis. Although APP is expressed in several tissues outside the human central nervous system, the functions of APP and its family members in other tissues are still poorly understood. APP is involved in several biological functions which might be potentially important for male fertility, such as cell adhesion, cell motility, signaling, and apoptosis. Furthermore, APP superfamily members are known to be associated with fertility. Knowledge on the protein networks of APP in human testis and spermatozoa will shed light on the function of APP in the male reproductive system. RESULTS: We performed a Yeast Two-Hybrid screen and a database search to study the interaction network of APP in human testis and sperm. To gain insights into the role of APP superfamily members in fertility, the study was extended to APP-like protein 2 (APLP2). We analyzed several topological properties of the APP interaction network and the biological and physiological properties of the proteins in the APP interaction network were also specified by gene ontologyand pathways analyses. We classified significant features related to the human male reproduction for the APP interacting proteins and identified modules of proteins with similar functional roles which may show cooperative behavior for male fertility. CONCLUSIONS: The present work provides the first report on the APP interactome in human testis. Our approach allowed the identification of novel interactions and recognition of key APP interacting proteins for male reproduction, particularly in sperm-oocyte interaction.