The Receptor for Activated C Kinase 1 (RACK1) is a member of the tryptophan-aspartate repeat (WD-repeat) family of proteins and shares significant homology to the β subunit of G-proteins (Gβ). RACK1 adopts a seven-bladed β-propeller structure which facilitates protein binding. RACK1 has a significant role to play in shuttling proteins around the cell, anchoring proteins at particular locations and in stabilising protein activity. It interacts with the ribosomal machinery, with several cell surface receptors and with proteins in the nucleus. As a result, RACK1 is a key mediator of various pathways and contributes to numerous aspects of cellular function. Here, we discuss RACK1 gene and structure and its role in specific signaling pathways, and address how posttranslational modifications facilitate subcellular location and translocation of RACK1. This review condenses several recent studies suggesting a role for RACK1 in physiological processes such as development, cell migration, central nervous system (CN) function and circadian rhythm as well as reviewing the role of RACK1 in disease.

Background and AimsInclusion of the mesentery during resection for colorectal cancer is associated with improved outcomes but has yet to be evaluated in Crohn’s disease. This study aimed to determine the rate of surgical recurrence after inclusion of mesentery during ileocolic resection for Crohn’s disease.MethodsSurgical recurrence rates were compared between two cohorts. Cohort A [n = 30] underwent conventional ileocolic resection where the mesentery was divided flush with the intestine. Cohort B [n = 34] underwent resection which included excision of the mesentery. The relationship between mesenteric disease severity and surgical recurrence was determined in a separate cohort [n = 94]. A mesenteric disease activity index was developed to quantify disease severity. This was correlated with the Crohn’s disease activity index and the fibrocyte percentage in circulating white cells.ResultsCumulative reoperation rates were 40% and 2.9% in cohorts A and B [P = 0.003], respectively. Surgical technique was an independent determinant of outcome [P = 0.007]. Length of resected intestine was shorter in cohort B, whilst lymph node yield was higher [12.25 ± 13 versus 2.4 ± 2.9, P = 0.002]. Advanced mesenteric disease predicted increased surgical recurrence [Hazard Ratio 4.7, 95% Confidence Interval: 1.71–13.01, P = 0.003]. The mesenteric disease activity index correlated with the mucosal disease activity index [r = 0.76, p < 0.0001] and the Crohn’s disease activity index [r = 0.70, p < 0.0001]. The mesenteric disease activity index was significantly worse in smokers and correlated with increases in circulating fibrocytes.ConclusionsInclusion of mesentery in ileocolic resection for Crohn’s disease is associated with reduced recurrence requiring reoperation.

The insulin receptor and insulin-like growth factor 1 receptor (IGF-1R), activated by their ligands, control metabolism, cell survival, and proliferation. Although the signaling pathways activated by these receptors are well characterized, regulation of their activity is poorly understood. To identify regulatory proteins we undertook a two-hybrid screen using the IGF-1R ␤-chain as bait. This screen identified Receptor for Activated C Kinases (RACK1) as an IGF-1R-interacting protein. RACK1 also interacted with the IGF-1R in fibroblasts and MCF-7 cells and with endogenous insulin receptor in COS cells. Interaction with the IGF-1R did not require tyrosine kinase activity or receptor autophosphorylation but did require serine 1248 in the C terminus. Overexpression of RACK1 in either R؉ fibroblasts or MCF-7 cells inhibited IGF-1-induced phosphorylation of Akt, whereas it enhanced phosphorylation of Erks and Jnks. Src, the p85 subunit of phosphatidylinositol 3-kinase, and SHP-2 were all associated with RACK1 in these cells. Interestingly, the proliferation of MCF-7 cells was enhanced by overexpression of RACK1, whereas IGF-1-mediated protection from etoposide killing was greatly reduced. Altogether the data indicate that RACK1 is an IGF-1R-interacting protein that can modulate receptor signaling and suggest that RACK1 has a particular role in regulating Akt activation and cell survival.The insulin and IGF-1 1 receptors (IR and IGF-1R) belong to a family of tyrosine kinase receptors that also includes the insulin-related receptor. They are tetrameric receptors made up of two ␣-subunits that bind the ligands insulin, IGF-1 or IGF-2, and two ␤-subunits that share high homology in their kinase domains (reviewed in Ref. 1). These receptors are homologous to a receptor found in the nematode Caenorhabditis elegans and in Drosophila, and they activate an evolutionarily conserved metabolic and survival signaling pathway that includes insulin-related substrate 1 (IRS-1), phosphatidylinositol 3-kinase (PI3-K), the serine/threonine kinase Akt, and the Forkhead family of transcription factors (2-5).

By comparing differential gene expression in the insulin-like growth factor (IGF)-IR null cell fibroblast cell line (R؊ cells) with cells overexpressing the IGF-IR (R؉ cells), we identified the INTRODUCTIONInsulin-like growth factor (IGF)-I and IGF-II are ligands for the widely expressed IGF-I receptor tyrosine kinase, which promotes mitogenesis and cell survival (reviewed in Adams et al., 2000). The IGF-IR is essential for normal growth during embryonic development and promotes cell survival and migration. Circulating IGFs and the IGF-IR signaling pathways also have been associated with cancer progression (reviewed in LeRoith and Roberts, 2003). In a mouse model of pancreatic islet cell tumorigenesis, endogenous IGF-IR expression was up-regulated at invasive regions of the tumors, and ectopic IGF-IR expression resulted in the accelerated development of highly invasive and metastatic carcinomas (Lopez and Hanahan, 2002). Conversely, the suppression of IGF-IR expression by antisense strategies (Resnicoff, 1998) or blocking antibodies results in decreased tumor growth and decreased metastatic capacity in tumor cell models (Maloney et al., 2003). Signals from the IGF-IR associated with survival, tumorigenicity, and metastasis are associated with the C terminus of the receptor (O'Connor et al., 1997;Brodt et al., 2001;Baserga et al., 2003).Cell migration and invasion are complex processes that require the coordination of signals from both adhesion and growth factor receptors. Signals from the IGF-IR can interact with those from integrins to initiate the formation of signaling complexes necessary for the formation and disassembly of cell adhesions with the extracellular matrix (ECM) (Doerr and Jones, 1996;Brooks et al., 1997). These signals involve enhancement of Shc phosphorylation (Mauro et al., 1999;Jackson et al., 2000;Kim et al., 2004), regulation of focal adhesion kinase phosphorylation at focal adhesions (Manes et al., 1999), differential regulation of signals by scaffolding proteins such as RACK1 (Hermanto et al., 2002;Kiely et al., 2002), signals from reorganization of the cytoskeleton (Casamassima and Rozengurt, 1998;Kim and Feldman, 1998;Guvakova et al., 2002), expression of angiogenic and invasive factors , regulation of cadherin location (Playford et al., 2000;Pennisi et al., 2002), and transactivation of the epidermal growth factor (EGF) receptor (Burgaud and Baserga, 1996;Roudabush et al., 2000). How all of these events are coordinated during cell migration or invasion, or how some of these signals are enhanced in metastatic cancer, is still poorly understood.IGF-I induces expression of several genes that promote cell migration and cancer progression, including ␤-catenin (Playford et al., 2000), the cadherin complex protein ZO-1 (Mauro et al., 2001), the angiogenic factor vascular endothelial growth factor (Miele et al., 2000), the metalloprotease MT1 MMP , and heparin-binding EGF-like growth factor (Mulligan et al., 2002 refractory to cellular transformation by several oncogenes (Sell et al., 1994), ...

FLIP is a potential anti-cancer therapeutic target that inhibits apoptosis by blocking caspase 8 activation by death receptors. We report a novel interaction between FLIP and the DNA repair protein Ku70 that regulates FLIP protein stability by inhibiting its polyubiquitination. Furthermore, we found that the histone deacetylase (HDAC) inhibitor Vorinostat (SAHA) enhances the acetylation of Ku70, thereby disrupting the FLIP/Ku70 complex and triggering FLIP polyubiquitination and degradation by the proteasome. Using in vitro and in vivo colorectal cancer models, we further demonstrated that SAHA-induced apoptosis is dependant on FLIP downregulation and caspase 8 activation. In addition, an HDAC6-specific inhibitor Tubacin recapitulated the effects of SAHA, suggesting that HDAC6 is a key regulator of Ku70 acetylation and FLIP protein stability. Thus, HDAC inhibitors with anti-HDAC6 activity act as efficient post-transcriptional suppressors of FLIP expression and may, therefore, effectively act as 'FLIP inhibitors'. Cell Death and Differentiation (2012) 19, 1317-1327 doi:10.1038/cdd.2012 published online 10 February 2012 FLIP is an anti-apoptotic protein that blocks the activation of apoptosis mediated by death receptors, such as Fas, TRAIL receptor 1 (TRAIL-R1/DR4) and TRAIL-R2 (DR5).1 By binding to the adaptor protein FADD, FLIP inhibits apoptosis by blocking the processing and activation of procaspase 8 (FLICE) by death receptor complexes termed DISCs (death-inducing signalling complexes). 2 We previously reported that FLIP inhibits apoptosis induced by chemotherapeutic agents 3 and that high FLIP expression is an independent adverse prognostic biomarker in colorectal cancer (CRC). 4 These and other studies have indicated that inhibition of FLIP constitutes a promising therapeutic strategy for the treatment of CRC. Ku70 and its binding partner Ku80 are critical components of the non-homologous end joining (NHEJ) DNA repair machinery.5 Ku70 is regulated by acetylation, which is mediated by the histone acetyl transferases (HATs); CREBbinding protein (CBP) and PCAF, and its acetylation can be enhanced by treating cells with histone deacetylase (HDAC) inhibitors.6 Ku70 acetylation disrupts its DNA-binding activity and sensitises cells to DNA-damaging agents. 7 In addition, cytoplasmic Ku70 binds to and regulates the pro-apoptotic Bcl-2 family member, Bax.6 Ku70 simultaneously inhibits Bax degradation via the ubiquitin proteasome system (UPS) and prevents its translocation to the mitochondria. 8 Moreover, it has been reported that Ku70 may have intrinsic deubiquitinating (DUB) activity.8 The Ku70-Bax complex is disrupted by Ku70 acetylation, which promotes Bax translocation to mitochondria and apoptosis induction. Herein, we report a novel interaction between FLIP and Ku70 that regulates FLIP stability. This interaction is acetylation-dependant and is disrupted by HDAC inhibitors with activity against HDAC6. Disruption of the Ku70-FLIP interaction subsequently leads to FLIP degradation by the UPS and induction of c...