Expression of the Novel Costimulatory Molecule B7-H5 in Pancreatic Cancer.

BACKGROUND: This study investigated how the B7-H5 protein, a new member of the B7 family, is expressed in normal human pancreas tissues and examined its expression changes in pancreatic cancer. METHODS: In this analysis, B7-H5 expression was examined by immunohistochemical staining of frozen specimens from patients undergoing pancreatic resection. RESULTS: Membranous B7-H5 protein was expressed on normal ductal epithelium within the pancreas. Other cell types from the normal pancreas, such as acinar cells and islet cells, did not express B7-H5. In adenocarcinoma, B7-H5 staining was decreased or absent. Interestingly, B7-H5 expression in intraductal papillary mucinous neoplasms varied with grade. No B7-H5 expression was found with other cancer types such as neuroendocrine tumors, but normal ducts adjacent to tumors were highly positive. CONCLUSIONS: The findings showed that B7-H5 expression was restricted to ductal cells in the normal pancreas and the expression was downregulated in pancreatic adenocarcinomas. In addition, the findings showed that B7-H5 expression changes within different stages of dysplasia. The study suggests that loss of the B7-H5 signal may contribute to immune evasion of pancreatic adenocarcinoma. However future studies are needed.

Proteasomal dysfunction activates the transcription factor SKN-1 and produces a selective oxidative-stress response in Caenorhabditis elegans.

SKN-1 in the nematode worm Caenorhabditis elegans is functionally orthologous to mammalian NRF2 [NF-E2 (nuclear factor-E2)-related factor 2], a protein regulating response to oxidative stress. We have examined both the expression and activity of SKN-1 in response to a variety of oxidative stressors and to down-regulation of specific gene targets by RNAi (RNA interference). We used an SKN-1-GFP (green fluorescent protein) translational fusion to record changes in both skn-1 expression and SKN-1 nuclear localization, and a gst-4-GFP transcriptional fusion to measure SKN-1 transcriptional activity. GST-4 (glutathione transferase-4) is involved in the Phase II oxidative stress response and its expression is lost in an skn-1(zu67) mutant. In the present study, we show that the regulation of skn-1 is tied to the protein-degradation machinery of the cell. RNAi-targeted removal of most proteasome subunits in C. elegans caused nuclear localization of SKN-1 and, in some cases, induced transcription of gst-4. Most intriguingly, RNAi knockdown of proteasome core subunits caused nuclear localization of SKN-1 and induced gst-4, whereas RNAi knockdown of proteasome regulatory subunits resulted in nuclear localization of SKN-1 but did not induce gst-4. RNAi knockdown of ubiquitin-specific hydrolases and chaperonin components also caused nuclear localization of SKN-1 and, in some cases, also induced gst-4 transcription. skn-1 activation by proteasome dysfunction could be occurring by one or several mechanisms: (i) the reduced processivity of dysfunctional proteasomes may allow oxidatively damaged by-products to build up, which, in turn, activate the skn-1 stress response; (ii) dysfunctional proteasomes may activate the skn-1 stress response by blocking the constitutive turnover of SKN-1; and (iii) dysfunctional proteasomes may activate an unidentified signalling pathway that feeds back to control the skn-1 stress response.

Activation of SKN-1 by novel kinases in Caenorhabditis elegans.

Here we use a large-scale RNAi suppression screen to identify additional kinases playing a role in the activation of SKN-1 in response to oxidative stress. The SKN-1 transcription factor specifies cell fate of the EMS blastomere at the four-cell stage in the nematode Caenorhabditis elegans and also directs transcription of many genes responding to oxidative stress, including glutathione S-transferase, NAD(P)H:quinone oxidoreductase, and superoxide dismutase. SKN-1 localizes to the nucleus and directs transcription following exposure to paraquat, heat, hyperbaric oxygen, and sodium azide. Previous studies have identified GSK-3 as an inhibitor of SKN-1 nuclear localization, in the absence of stress, and PMK-1 as an activator of SKN-1 during periods of oxidative stress. Through this screen we have identified four kinases, MKK-4, IKK epsilon-1, NEKL-2, and PDHK-2, which are necessary for the nuclear localization of SKN-1 in response to oxidative stress. Inhibition of two of these kinases results in shorter life span and increased sensitivity to stress.