Using kinomics to delineate signaling pathways: control of CRTC2/TORC2 by the AMPK family.

The classical role of AMP-activated protein kinase (AMPK) as an energy status sensor is expanding to include other members of the AMPK family. Recent genetic and cell biological evidence points to a role for MAP/microtubule affinity-regulating kinase 2 (MARK2/EMK/Par1b) in the regulation of metabolic events as well as in the control of CREB-dependent transcription activated by glucose in pancreatic islet beta cells. We have recently developed an in vitro kinase screening platform to identify novel kinase:substrate pairs, the building blocks of signal transduction pathways.

IAP-targeted therapies for cancer.

DNA damage, chromosomal abnormalities, oncogene activation, viral infection, substrate detachment and hypoxia can all trigger apoptosis in normal cells. However, cancer cells acquire mutations that allow them to survive these threats that are part and parcel of the transformation process or that may affect the growth and dissemination of the tumor. Eventually, cancer cells accumulate further mutations that make them resistant to apoptosis mediated by standard cytotoxic chemotherapy or radiotherapy.

hnRNP A1 regulates UV-induced NF-kappaB signalling through destabilization of cIAP1 mRNA.

cIAP1 is an important member of the inhibitor of apoptosis family of proteins and is involved in the regulation of the NF-kappaB-signalling pathway downstream of the TNF receptor. We report here that UV irradiation leads to downregulation of cIAP1 expression because of enhanced cIAP1 mRNA destabilization. An AU-rich element located within the 3' untranslated region of cIAP1 mRNA is sufficient to mediate cIAP1 mRNA instability.

Both cIAP1 and cIAP2 regulate TNFalpha-mediated NF-kappaB activation.

The cellular inhibitor of apoptosis 1 and 2 (cIAP1 and cIAP2) proteins have been implicated in the activation of NF-kappaB by TNFalpha; however, genetic deletion of either cIAP1 or 2 did not support a physiologically relevant role, perhaps because of functional redundancy. To address this, we used combined genetic and siRNA knockdown approaches and report that cIAP1 and 2 are indeed critical, yet redundant, regulators of NF-kappaB activation upon TNFalpha treatment. Whereas NF-kappaB was properly activated by TNFalpha in cultured and primary cells deficient in either cIAP1 or 2, removal of both cIAPs severely blunted its activation.

Glucose controls CREB activity in islet cells via regulated phosphorylation of TORC2.

CREB is a cAMP- and calcium-responsive transcriptional activator that is required for islet beta cell proliferation and survival. Glucose and incretin hormones elicit beta cell insulin secretion and promote synergistic CREB activity by inducing the nuclear relocalization of TORC2 (also known as Crtc2), a coactivator for CREB. In islet cells under basal conditions when CREB activity is low, TORC2 is phosphorylated and sequestered in the cytoplasm by 14-3-3 proteins.

The RING domain of cIAP1 mediates the degradation of RING-bearing inhibitor of apoptosis proteins by distinct pathways.

The Inhibitor of Apoptosis proteins (IAPs) are key repressors of apoptosis. Several IAP proteins contain a RING domain that functions as an E3 ubiquitin ligase involved in the ubiquitin-proteasome pathway. Here we investigated the interplay of ubiquitin-proteasome pathway and RING-mediated IAP turnover.

Proteasome inhibition as a novel therapy in treating rheumatoid arthritis.

Rheumatoid arthritis (RA) is an erosive joint disease affecting about 1% of the population. The joint destruction is primarily mediated by special cells called fibroblast-like synoviocytes (FLS), which undergo an expansion forming a pannus that destroys the joint. Apoptosis has been rarely detected in the synovial lining.

The eIF4G homolog DAP5/p97 supports the translation of select mRNAs during endoplasmic reticulum stress.

DAP5/p97 is a member of the eIF4G family of translation initiation factors that has been suggested to play an important role in the translation of select messenger RNA molecules. We have shown previously that the caspase-cleaved form of DAP5/p97, termed p86, is required for the induction of the endoplasmic reticulum (ER)-stress-responsive internal ribosome entry site (IRES) of the caspase inhibitor HIAP2. We show here that expression of DAP5/p97 is enhanced during ER stress by selective recruitment of DAP5/p97 mRNA into polysomes via the DAP5/p97 IRES.

Cap-independent regulation of gene expression in apoptosis.

Expression of the proteome is tightly regulated at the level of protein synthesis. Translational control is a critical homeostatic mechanism that allows the cell to rapidly change its phenotype in the face of an intra- and extra-cellular environment in constant flux. It is becoming increasingly clear that when it comes to protein translation during cell stress, all mRNAs are not treated equally.

For IRES trans-acting factors, it is all about location.

The translation of many proteins involved in transcription, cell cycle progression, apoptosis and cell survival is mediated by internal ribosome entry sites (IRESs) present within the 5'-untranslated regions (5'-UTRs) of their messenger RNA molecules (mRNAs). Several recent reports now demonstrate that the proteins controlling IRES-dependent translation initiation are regulated by their subcellular localization.

The role of XAF1 in cancer.

The inhibitors of apoptosis (IAP) proteins have emerged as important cancer targets. The cellular control of IAP expression is regulated by survival signaling pathways and by a variety of known intrinsic antagonists. Among these antagonists, the X-linked IAP-associated factor (XAF)1 is unique in its control of IAP function and in its ability to sensitize cancer cells to apoptosis.

Degradation of survivin by the X-linked inhibitor of apoptosis (XIAP)-XAF1 complex.

X-linked inhibitor of apoptosis (XIAP)-associated factor 1 (XAF1) is a putative tumor suppressor in which expression is significantly reduced in human cancer cell lines and primary tumors. The proapoptotic effects of XAF1 have been attributed to both caspase-dependent and -independent means. In particular, XAF1 reverses the anti-caspase activity of XIAP, a physiological inhibitor of apoptosis.

The inhibitors of apoptosis (IAPs) as cancer targets.

Apoptosis has been accepted as a fundamental component in the pathogenesis of cancer, in addition to other human diseases including neurodegeneration, coronary disease and diabetes. The origin of cancer involves deregulated cellular proliferation and the suppression of apoptotic processes, ultimately leading to tumor establishment and growth. Several lines of evidence point toward the IAP family of proteins playing a role in oncogenesis, via their effective suppression of apoptosis.

Subcellular relocalization of a trans-acting factor regulates XIAP IRES-dependent translation.

Translation of the X-linked inhibitor of apoptosis (XIAP) proceeds by internal ribosome entry site (IRES)-mediated initiation, a process that is physiologically important because XIAP expression is essential for cell survival under conditions of compromised cap-dependent translation, such as cellular stress. The regulation of internal initiation requires the interaction of IRES trans-acting factors (ITAFs) with the IRES element. We used RNA-affinity chromatography to identify XIAP ITAFs and isolated the heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1).

Involvement of caspase-2 and caspase-9 in endoplasmic reticulum stress-induced apoptosis: a role for the IAPs.

Dysregulation of apoptosis is involved in a wide spectrum of disease ranging from proliferative to degenerative disorders. An emerging area of study in apoptosis is the critical contribution of the endoplasmic reticulum (ER) in both mitochondrial and ER specific apoptosis pathways. Here we show that brefeldin A and tunicamycin-mediated ER stress lead to caspase-dependent apoptosis involving caspase-2.

Abnormalities of cell structures in tumors: apoptosis in tumors.

A conceptual shift has occurred in recent years from considering cancer as simply a disease of deregulated cell proliferation to a view that incorporates the aberrant control of apoptosis into the equation. Apoptosis is an organized, genetically programmed cell death process by which multicellular organisms specifically destroy, dismantle and dispose of cells. In cancer cells, this tightly controlled process is suppressed by genetic lesions, allowing cancer cells to survive beyond their normal life span even in hostile environments that are prone to hypoxia and lack many trophic factor supports.