Monomerization of cytosolic mature smac attenuates interaction with IAPs and potentiation of caspase activation

Immunohistochemical expression of X-linked inhibitor of apoptosis in eyelid sebaceous gland carcinoma predicts a worse prognosis

Purpose:

Overexpression of the inhibitors of apoptosis proteins have been demonstrated in a variety and of solid tumors including melanomas and nonmelanomas skin cancers. X-linked inhibitor of apoptosis protein (XIAP) is an inhibitor of apoptosis which prevents apoptosis by inhibiting caspases 9, 7, and 3. The prognostic value of XIAP in sebaceous gland carcinoma (SGC) remains unexplored.

Methods:

The immunohistochemical expression of XIAP was evaluated in 29 SGC cases.

Results:

The cytoplasmic overexpression of XIAP was detected in 62% SGC cases. XIAP expression was found to be significantly associated with advanced age, large tumor size, and with reduced disease-free survival (P = 0.0174). XIAP expression and advance tumor Grade III emerged as significant risk factors on univariate analysis. On stepwise multivariate analysis, both increased cytoplasmic XIAP expression and high tumor grade were found to be significantly associated with recurrence. Patients with low XIAP immunoexpression had a longer disease-specific survival than those with high expression in the 5-year follow-up.

Conclusion:

The present study demonstrates at the immunohistochemical level that XIAP is overexpressed in SGC and that high expression could be of biological significance in the development of eyelid SGC. Our finding suggests that up-regulation of XIAP may aggravate tumor metastasis in SGC.

Ectopic expression of new alternative splice variant of Smac/DIABLO increases mammospheres formation

Smac-α is a mitochondrial protein that, during apoptosis, is translocated to the cytoplasm, where it negatively regulates members of the inhibitor of apoptosis (IAP) family via the IAP-binding motif (IBM) contained within its amino-terminus. Here, we describe a new alternative splice variant from Smac gene, which we have named Smac-ε. Smac-ε lacks both an IBM and a mitochondrial-targeting signal (MTS) element. Smac-ε mRNA exhibits a tissue-specific expression pattern in healthy human tissues as well as in several cancer cell lines. The steady-state levels of endogenous Smac-ε protein is regulated by the proteasomal pathway. When ectopically expressed, this isoform presents a cytosolic localization and is unable to associate with or to regulate the expression of X-linked Inhibitor of apoptosis protein, the best-studied member of IAP family. Nevertheless, over-expression of Smac-ε increases mammosphere formation. Whole genome expression analyses from these mammospheres show activation of several pro-survival and growth pathways, including Estrogen-Receptor signaling. In conclusion, our results support the functionality of this new Smac isoform.

Diablo/SMAC: a novel biomarker of pollutant exposure in European flounder (Platichthys flesus)

Diablo (or SMAC) is a protein released from mitochondria following apoptotic stimuli and inhibits the actions of Inhibitors of Apoptosis (IAP) proteins. IAPs regulate the activity of caspases and NFkB, the primary executioners of apoptosis and of inflammation, respectively. Thus, Diablo is important for the regulation of cellular responses to damage. In Northern Europe, statutory governmental marine monitoring programs measure various biomarkers in flounder to indicate biological effects of pollutant exposure. More recently transcriptomic techniques have been applied in flounder to gain a more comprehensive understanding of pollutant effects, and to discover novel biomarkers. In most of these studies utilising flounder, Diablo was amongst the most highly increased transcripts identified. The aim of this study was to further examine piscine Diablo, at the gene level and mRNA level, after exposure to prototypical pollutants, and in flounder caught from polluted environments. The results show that two genes encoding Diablo exist in fish species, and in flounder one of these genes is increased in liver after exposure to polyaromatic hydrocarbons and polychlorinated biphenyls, and also in livers from fish living on contaminated estuarine sediments. Therefore, Diablo measurement has potential as a biomarker of pollutant exposure, and could indicate damaging effects of chemical contaminants.