While we found that both constitutive
p subunits and their inducible counterparts were expressed in the testis and epididymis, only the constitutional subunits showed significant expression changes in the tissues of the exposed animals. Products of two of the three examined UPP enzyme genes not directly associated with the proteasome, the Ubel and Ube2d3 genes, also showed significant changes overall or in some segments. This indicates that the screening of the ubiquitin system provides valuable information about the effect of toxic exposure on the male reproductive system.
In the future, we will explore the simultaneous screening of all 19S, 20S, and 11S subunits as well as an expanded repertoire of ubiquitin-conjugating and deubiquitinating enzymes. Such an analysis could be greatly facilitated by automated transcriptional profiling—for example, by a microarray designed specifically to capture all gene products within the UPP.
In summary, our data indicate that DNB and THP exposures alter the expression of select genes within the UPP in a time-and dose-dependent manner. In particular, the Psmbl, Psmb2, Psmb5, and Ube2d3 genes that encode the constitutive proteasomal core and ubiquitin-activating enzyme UBE2 were affected. This change is most significant in the testis and corpus epididymis, but the magnitude of effect differs slightly by the administered toxicant. Such an altered gene expression may correlate with aberrant spermatogenesis in the testis and impair the processing of both normal and defective spermatozoa in the epididymis. Transcriptional profiling and flow cytometric analysis of the UPP thus capture the subtle effects of reproductive toxicity not observed by conventional histology and functional cytology and offer a prospective new tool to detect and manage reproductive toxicology. In addition to mapping the effect of reprotoxic exposure on the expression of a specific subset of functionally related genes in the testis and epididymis, the present study showed a gradient in the expression of the UPP pathway genes that, for most genes, seemed to follow the pattern of testis > caput > corpus > cauda or caput > testis > corpus > cauda.