5B,C). What might be the Selleck Crizotinib role of AEG-1 in RISC? The lack of any enzymatic domain indicates that AEG-1 might be a scaffold protein favoring formation of complex multiprotein structures such as RISC.

We identified that the region of AEG-1 protein containing a.a. 101-205 interacts with SND1. Interestingly, the same region also interacts with p65 subunit of nuclear factor kappaB (NF-κB) and a.a. 72-169 interacts with another AEG-1 interacting protein, BCCIPα.14, 20 Bioinformatic analysis could not identify any known potential protein/protein interaction domain or motif in this region of AEG-1, indicating that this region might be a unique and novel protein/protein interaction domain. Mutational

analysis of this region will help identify which amino acid residues of AEG-1 are critical for mediating these interactions and thus might be potential hot spots that might be targeted by small molecules to inhibit AEG-1 function. Apart from a few isolated studies, little is known about the role of SND1 in tumorigenesis. As such, we were surprised to find the relatively high expression of SND1 in human HCC samples compared to normal liver. Indeed, we observed that overexpression of SND1 in Hep3B cells, expressing a low level of SND1, augments, whereas inhibition of SND1 in QGY-7703 cells, expressing a high level of SND1, abrogates in vitro viability and in vivo tumorigenicity in nude mice. We also observed that inhibition of enzymatic (nuclease) activity of SND1 RG7420 mw by the chemical inhibitor pdTp decreases viability of human HCC cells, indicating that functional SND1, or functional RISC activity, is required for maintaining cell viability. Our findings are supported by a recent study demonstrating that SND1 is cleaved by caspases during drug-induced

apoptosis.21 A noncleavable SND1 mutant increased cell viability and knocking down SND1 promoted drug-induced apoptosis in HeLa cells.21 Incubation with caspases completely blocked RNase activity of SND1, MCE indicating that SND1 enzymatic activity is required for maintaining cell viability or protection from apoptosis. Hepatocellular carcinoma is one of the top five malignancies worldwide.22 The advanced disease is highly resistant to standard radio- and chemotherapy and virtually no effective treatment is available even for palliative treatment. Identification of novel targets thus facilitates development of new modalities of effective treatment for this fatal disease. Screening for small molecule inhibitors of SND1 enzymatic activity with a clinically achievable dose might usher in an effective therapeutic regimen not only for HCC but also for other SND1-overexpressing tumors.