In this respect, a previous report showed that TNF-�� can activate c-Abl and upregulate apoptotic p73 function via a caspase-dependent elimination of retinoblastoma protein, and thus unleashing the nuclear apoptotic effector, c-Abl [8]. Currently the molecular events linking caspase to non-cleaved c-Abl activation following TRAIL stimulation remains unknown, and despite further investigation is required. In contrast to reduced TRAIL sensitivity in colon cancer cells, STI571 did not change the susceptibility of PC3 and LNCaP cells to TRAIL. We ruled out such cell type-specific effects of STI571 being related to c-Abl protein expression. Similar expression levels of c-Abl were observed in HCT116, SW480, PC3, and LNCaP cells (data not shown).

Instead, we suggest that the antitumor activity of TRAIL in colon and prostate cancers might involve distinctive regulation and complex apoptotic pathways. In prostate cancers, neither p38 nor JNK activation by TRAIL is involved in cell death, while STI571 can still slightly inhibit TRAIL-induced JNK activation in prostate cancers. Moreover, TRAIL-mediated c-Abl cleavage displayed the same pattern in HCT116 and LNCaP cells. Therefore, these results further support the notion that the cell type-specific effect of STI571 on antitumor activity of TRAIL is dependent on the roles of p38 and JNK in cell death per se. Conclusions We demonstrate a novel mediator role of p73 in activating the stress kinases, p38 and JNK, in the apoptotic pathway of TRAIL (Figure (Figure7).7).

This action is initiated by caspase-dependent c-Abl activation, and is a key mechanism contributing to death receptor-mediated cell apoptosis in colon cancer, but not prostate cancer cells. Through inhibition of the c-Abl-mediated apoptotic p73 signaling, STI571 reduces the antitumor activity of TRAIL. In this sense, this study is not in favor of the cocktail therapy of STI571 and TRAIL in human colon cancers, and also highlights the cancer-specific effect of stress kinases on the antitumor activities of TRAIL. Figure 7 Signaling pathway for the cytoprotective effect of STI571 in TRAIL-treated colon cancer cells. In addition to induce classical apoptotic cascade elicited by caspases, TRAIL-induced apoptosis in colon cancer cells requires p38 and JNK activation. We propose …

Abbreviations CML: Chronic myelogenous leukemia; DR: Death receptor; FADD: Fas-associated protein with death domain; FasL: Fas ligand; JNK: c-Jun Anacetrapib NH2-terminal kinase; MAPK: Mitogen-activated protein kinase; MEKK: Mitogen-activated protein kinase kinase; MTT: 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyltetrazolium bromide; PI: Propidium iodide; RB: Retinoblastoma; RIP: Receptor-interacting protein; TNF-��: Tumor necrotic factor-��; TRAF2: TNF receptor-associated factor 2; TRAIL: TNF-related apoptosis-inducing ligand; zVAD: z-Val-Ala-Asp-fluromethylketone. Competing interests The authors declare that they have no competing interests.

Results 8 MPEG-PL-Cy5.5 Probe Characterization In order to determine trypsin activation in experimental pancreatitis using the caerulein model, we developed a probe that was selective to trypsin activity. To evaluate the mechanism of action, in vivo, of trypsin inhibitor drug-like compounds, we prepared a self-quenched selleck chemicals llc trypsin activatable near infrared smart probe. When rat anionic trypsin was added to 1 ��M of mPEG-PL-Cy5.5 probe, increase in fluorescence intensity was observed which was positively correlated to the concentration of trypsin enzyme and the time of incubation. To establish trypsin selectivity, mPEG-PL-Cy5.5 probe activation was tested by addition to a panel of endopeptidases that are described to be expressed in the pancreas, including human and rat pancreatic elastase, kallikrein 1, kallikrein 5, chymotrypsin, cathepsin L, and cathepsin B [22].

As shown in figure 1, mPEG-PL-Cy5.5 probe was activated in the presence of trypsin in contrast to other pancreatic enzymes. In the presence of the highly specific trypsin inhibiting protein SPINK1, the protease activation was suppressed to background levels (figure 1). Therefore, it can be concluded that mPEG-PL-Cy5.5 probe was highly trypsin selective. Figure 1 MPEG-PL-Cy5.5 probe characterization. 9 In Vivo Monitoring of Trypsin Activation 9.1 Model development The caerulein-injection model is a well-established mechanistic model for experimental pancreatitis. For optical imaging, however, the anatomical location of the pancreas posed a challenge to signal acquisition.

Animal weight and age were critical when choosing subjects for optical imaging study. Adult rats were considered the most suitable because of their smaller stomach size and separation of the pancreas and stomach. Upon administration of caerulein in rats, edema development is observed. We administered a blood pool imaging agent Angiosense 680 to confirm our ability to image pancreas non-invasively in rats. Healthy animals that were subjected to repeated doses of caerulein showed increasing accumulation of the blood pool agent Angiosense 680. The graph in figure 2a shows a threefold enhancement in Angiosense 680 signal in the pancreas normalized to signal acquired before caerulein administration. Therefore, for these studies, three caerulein administrations were sufficient. Figure 2 In vivo pancreatitis imaging of edema (A) and trypsin activation (B).

Establishing the ability to image diseased pancreas in a rat model using optical imaging, we evaluated the time course and severity of trypsin activation in this experimental pancreatitis model using the trypsin activatable mPEG-PL-Cy5.5 probe. 9.2 Trypsin dependent activation of mPEG-PL-Cy5.5 probe MPEG-PL-Cy5.5 probe was administered to healthy animals and then three hourly repeated caerulein injections were GSK-3 administered to evaluate the time and severity of trypsin activation. MPEG-PL-Cy5.