Background: Our aim was to determine if changes in ubiquitin are correlated with proteins known to be affected directly or indirectly by the ubiquitin-proteasome pathway. For example, the intermediary kinase of the NFκβ pathway IKK is tagged directly by ubiquitin, aiding its degradation within the large, self-compartmentalised protease called the 26S proteasome. IKK degradation allows the release of NFκβ (an indirect consequence of ubiquitination) that then translocates into the nucleus to initiate the transcription of survival factors such as cIAP2, BCL-XL, BFL1, FLIP, IL-8, and TNF-α.
Methods: Lyophilised baboon endometrial tissues from the University of Illinois at Chicago (UIC) and from women undergoing laparoscopy from the Sydney South West Area of Health Service (SSWAHS) were processed for RNA extraction and analysis. Immunohistochemical studies were also conducted on formalin fixed baboon and human endometrial tissues from UIC and from the Sydney West Area Health Service (SWAHS).
Results: IKKα immunostaining were elevated in the cytoplasm of glands during late follicular phase and stromal cells during menses in the baboon, whilst proteasome was elevated in the nucleus of glands and stroma at menses, as well as within the glandular cytoplasm of endometriotic tissues. Comparable levels of Iκβα exists throughout the menstrual cycle of the eutopic endometrium, whilst a reduced glandular nuclear Iκβα was seen in endometriotic tissues of the animal model. TNF-α was increased within stromal cells at menses but was equivalent between the eutopic and ectopic endometrium. Ubiquitin was similar between LF and mid luteal phase of eutopic glands and stroma, as well as between eutopic and ectopic endometrium at mid luteal. IKKβ and NFκβ levels were alike within eutopic and ectopic tissues throughout the menstrual cycle. In women however, IKKα, IKKβ, Iκβα and NFκβ had comparable levels within all cell types and cycle phases, whilst a greater proteasome immunostaining was seen in the nucleus of eutopic stromal cells at secretory phase, as well as in the nucleus of ectopic stromal cells at proliferative phase. However, the nucleus of stromal cells and glandular cytoplasm of endometriotic tissues both had lower proteasome levels during the secretory phase.
Conclusions: In this study, IKKα had a greater potential to activate the p65 subunit of NFκβ in ectopic stromal cells than IKKβ and TNF-α did not seem to be correlated with greater free ubiquitin expression in endometriosis in the baboon. This suggests that IKKα is a likely candidate for ectopic stromal cell survival in endometriosis in the animal model but this is unlikely to be mediated by the ubiquitin NFκβ pathway. Similarly, in women with endometriosis a different pathway to NFκβ is potentially responsible for a greater ectopic cell survival potential, however an increased patient cohort is required to definitively ascertain the involvement of IKKα in the future.