Expression, Localization of SUMO-1, and Analyses of Potential SUMOylated Proteins in Bubalus bubalis Spermatozoa

Identifying new sperm Western blot loading controls

The measurement of protein expression level plays a pivotal role in both biological and medical studies. Housekeeping proteins, generally encoded by housekeeping genes are used as loading control proteins to normalize protein expression. Obviously, proper reference standards are essential for adequate analysis of protein expression. However, our study showed that the widely used normalisation proteins, whose expression levels varied greatly among sperm samples, were unsuitable for data standardisation. To uncover the proteins steadily expressed in sperm, we analysed several published transcriptome data of sperm. Seven proteins whose expression levels were relatively stable (co-efficient variation values less than 0.35) were selected and further evaluated by quantitative real-time polymerase chain reaction, Western Blot (WB) and immunocytochemistry. Our results showed that among the classical housekeeping proteins, only β-tubulin remained constant in sperm samples from 85 individuals. Compared with other classical housekeeping proteins such as glyceraldehyde 3-phosphate dehydrogenase, actin and histone H3, Cullin-1 (CUL1) and F-box only protein 7 (FBXO7) seemed to be more suitable to be used as internal controls for WB in sperm protein studies. Combined with the locations of these proteins, CUL1 and FBXO7 were suggested to be used as a housekeeping protein for total proteins.

4-tert-octylphenol injures motility and viability of human sperm by affecting cAMP-PKA/PKC-tyrosine phosphorylation signals

4-tert-octylphenol (4t-OP) is a well-known xenoestrogen. Our objective was to explore the effects and molecular mechanisms of 4t-OP on human sperm. Sperm samples were exposed to 0, 0.1, or 0.3 mM 4t-OP for two hours. Results showed that both sperm viability and motility were significantly injured by 0.3 mM 4t-OP. We applied comparative proteomics to explore the molecular targets affected by 4t-OP. 81 differentially expressed (DE) proteins were identified. Bioinformatic analysis showed that these proteins were highly associated with motility and apoptosis, and were mostly enriched in cAMP-PKA/PKC-phosphorylation-associated pathway. We further verified that 0.1 mM and 0.3 mM 4t-OP significantly decreased cAMP activity of sperm. Expression of RACK1 and PRDX6 were detected by western blot (WB) to verify their tendencies in gels; antiapoptotic factor BCL2 was also detected by WB. The data indicated that 4-tert-octylphenol injures the motility and viability of human sperm probably by affecting cAMP-PKA/PKC-tyrosine phosphorylation signals.