Inducible proteasomal core subunits PSMB9, PMSB8, and PSMB10 replace their constitutive counterparts PMSB5, PMSB1, and PMSB2 in the professional antigen-presenting cells but are also present in other cell types, such as eye lens cells and the sperm acrosome. The expression of inducible subunit Pmsb8 as measured by semiquantitative RT was significantly reduced within the testis and corpus epididymis of the THP-exposed rats, and yet overall, the changes in the expression of the other two inducible subunits were not significant. It is possible that the inducible subunit genes are less sensitive to THP.
The loss of inducible 20S subunit transcripts could also be masked by an increased infiltration of white blood cells expressing inducible subunits in the testicular or epididymal tissues of exposed animals; such a white blood cell infiltration, however, was not detected by our histological analysis. Only Psmbl, Psmb2, and Psmb5 and the genes encoding for the constitutive 20S proteasomal core subunits and the Ube2d3 gene showed significant expression level changes between the control and treated samples when all segments were analyzed simultaneously.