Although p53 transcriptional activation potential is critical for its ability to
Although p53 transcriptional activation potential is critical for its ability to suppress cancer, the specific target genes involved in tumor suppression remain unclear. individual survival. SIVA functions independently of p53, and instead, stimulates mTOR signaling and metabolism in NSCLC cells. Thus, SIVA enables tumorigenesis in a p53-impartial manner, exposing a potential new cancer therapy target. null mice develop malignancy with 100% penetrance (1). p53 Ki16425 is usually a cellular stress sensor that triggers various cellular responses, including apoptosis, cell-cycle arrest, and autophagy (2, 3), in response to diverse stress signals, including DNA damage, hyperproliferative stimuli, and nutrient deprivation, as a measure to restrain tumorigenesis (1, 4). While activation of apoptosis helps to eliminate defective cells, induction of cell-cycle arrest and the associated DNA repair program helps to maintain the genetic integrity of cells and cell survival (2). p53 relies primarily on its function as a transcriptional activator to trigger these different responses through induction of a host of different target genes (1, 4). While the specific target genes involved in cell-cycle arrest and apoptosis have been well characterized, the p53 target genes critical for tumor suppression remain incompletely comprehended (4, 5). Intriguingly, although transcriptional activation potential is critical for p53-mediated tumor suppression, canonical p53 target genes, such as and are dispensable for tumor suppression (6C8). Thus, important mediators of p53 tumor suppressor activity remain to be recognized. SIVA is usually a pro-apoptotic protein originally recognized by virtue of its conversation with CD27 and other death receptors (9, 10). It was subsequently shown to be a direct p53 target gene that is specifically upregulated to high levels during apoptosis relative to G1 cell-cycle arrest (11, 12). In addition, SIVA plays an important role in p53-dependent apoptosis as loss of SIVA in cerebellar granular neurons (CGNs) compromises DNA-damage-induced, p53-dependent apoptosis (11). Ki16425 Furthermore, overexpression of SIVA in CGNs, mouse embryonic fibroblasts (MEFs), and lymphocytes is sufficient to induce cell death (11, 13). In CGNs exposed to DNA damage, SIVA localizes to the plasma membrane and induces apoptosis in a manner dependent on BID and BAX/BAK (11), consistent with SIVA acting through both the extrinsic and intrinsic cell death pathways. This pro-apoptotic function suggests that SIVA may itself have tumor suppressor activity. Beyond its role in restraining cellular growth through apoptosis, several lines of evidence suggest that SIVA also promotes ERCC3 proliferation. Such as, is usually directly transcriptionally activated by E2F1, a protein essential for promoting cell cycle progression (12). In addition, SIVA has been reported to suppress p53 activity by stabilizing the conversation between MDM2 and p53, leading to increased p53 ubiquitination and degradation, and increased BrdU incorporation (14). SIVA can also act as an E3-ubiquitin ligase for the p53-activating protein p19ARF, thereby promoting p19ARF degradation, and consequently provoking p53 destabilization and enhanced cellular proliferation (15). Thus, these studies Ki16425 collectively suggest that SIVA could play a tumor-promoting role. To explore whether SIVA exerts a tumor-suppressive or tumor-promoting role downstream of p53, we assessed the effect of SIVA loss in a mouse model of oncogenic KRAS-driven non-small cell lung malignancy (NSCLC) development, in which p53 plays a key role in suppressing malignant progression. Using conditional knockout mice that we generated, we found that SIVA is necessary for efficient oncogenic KRAS-driven NSCLC development. Subsequent analysis of SIVA function revealed that knockdown dampens proliferation and transformation in both mouse and human NSCLC cell lines. The diminished proliferation and transformation upon SIVA knockdown are impartial of p53, and instead are associated with decreased metabolic function. These findings show that SIVA plays a p53-impartial role in enabling lung malignancy development and suggest the possibility that it could ultimately be a target Ki16425 for malignancy therapy. Results Generation of Conditional Knockout Mice To analyze the role of SIVA in tumorigenesis conditional knockout mice. Mouse embryonic stem (ES) cells were targeted such that the entire locus, comprising four exons, was flanked by a LoxP and a Lox-Puro-Lox cassette, ensuring complete deletion of the gene (Fig. 1A). Proper targeting of ES cells was confirmed by.