IEX -1L, an Apoptosis Inhibitor Involved in NF-κB-Mediated Cell Survival

A mild insult to the brain can sometimes trigger secondary brain injury, causing severe postconcussion syndrome, but the underlying mechanism is ill understood. We show here that secondary brain injury occurs consistently in mice lacking immediate early responsive gene X-1 (IEX-1), after a gentle impact to the head, which closely simulates mild traumatic brain injury in humans. The pathologic lesion was characterized by extensive cell death, widespread leukocyte infiltrates, and severe tissue loss. On the contrary, a similar insult did not induce any secondary injury in wild-type mice. Strikingly, noninvasive exposure of the injured head to a low-level laser at 4 hours after injury almost completely prevented the secondary brain injury in IEX-1 knockout mice. The low-level laser therapy (LLLT) suppressed proinflammatory cytokine expression like interleukin (IL)-1b and IL-6 but upregulated TNF-a. Moreover, although lack of IEX-1 compromised ATP synthesis, LLLT elevated its production in injured brain. The protective effect of LLLT may be ascribed to enhanced ATP production and selective modulation of proinflammatory mediators. This new closed head injury model provides an excellent tool to investigate the pathogenesis of secondary brain injury as well as the mechanism underlying the beneficial effect of LLLT.

Cyclooxygenase-2 (COX-2) is selectively overexpressed in colorectal tumours. The mechanism of COX-2 induction is not fully understood, but requires de novo messenger RNA and protein synthesis, indicating regulation at the transcriptional level. Sequence analysis of the 5 0 -flanking region of the COX-2 gene shows two nuclear factor-kB (NF-kB) sites. Inhibition of this protein in model cell culture systems attenuates COX-2 expression and implies that NF-kB plays an important role in COX-2 induction. We measured COX-2, NF-kB and IkB kinase a (IKKa) protein expression in matched colonic biopsy samples comprising both nontumour and adjacent tumour tissue from 32 colorectal cancer patients using immunohistochemistry. There was none or very little expression of COX-2, NF-kB and IKKa in non-neoplastic colon epithelial cells, while the expression of all three of these proteins was significantly increased (Po0.05, Wilcoxon's signed rank test) in adjacent cancerous cells. Moreover, all three proteins were found to be coexpressed in the neoplastic epithelium, with the expression of COX-2 and NF-kB highly correlated (Pearson's correlation, Po0.005). There was no apparent correlation between enhanced COX-2, NF-kB or IKKa expression and tumour Dukes' stages. Our results are compatible with the hypothesis that IKKa and NF-kB are involved in COX-2 induction in these tumours and the lack of association between COX-2 expression and severity of disease as measured by Dukes' stage is consistent with the proposal that COX-2 expression is an early postinitiation event.

Caspase 8 is the most proximal caspase in the caspase cascade and has been known for its role in the mediation of cell death by various death receptors belonging to the TNFR family. We have discovered that Caspase 8 can activate the NF-kB pathway independent of its activity as a pro-apoptotic protease. This property is localized to its N-terminal prodomain, which contains two homologous death e ector domains (DEDs). Caspase 10 and MRIT, two DEDs-containing homologs of Caspase 8, can similarly activate the NF-kB pathway. Dominantnegative mutants of the Caspase 8 prodomain can block NF-kB induced by Caspase 8, FADD and several death receptors belonging to the TNFR family. Caspase 8 can interact with multiple proteins known to be involved in the activation of the NF-kB pathway, including the serine-threonine kinases RIP, NIK, IKK1 and IKK2. Thus, DEDs-containing caspases and caspase homolog(s) may have functions beyond their known role in the mediation of cell death. Oncogene (2000) 19, 4451 ± 4460.