Milad S. Bitar

Raf Kinase Inhibitor Protein RKIP Enhances Signaling by Glycogen Synthase Kinase-3β

Raf kinase inhibitory protein (RKIP) is a physiologic inhibitor of c-RAF kinase and nuclear factor κB signaling that represses tumor invasion and metastasis. Glycogen synthase kinase-3β (GSK3β) suppresses tumor progression by downregulating multiple oncogenic pathways including Wnt signaling and cyclin D1 activation. Here, we show that RKIP binds GSK3 proteins and maintains GSK3β protein levels and its active form. Depletion of RKIP augments oxidative stress-mediated activation of the p38 mitogen activated protein kinase, which, in turn, inactivates GSK3β by phosphorylating it at the inhibitory T390 residue. This pathway de-represses GSK3β inhibition of oncogenic substrates causing stabilization of cyclin D, which induces cell-cycle progression and β-catenin, SNAIL, and SLUG, which promote epithelial to mesenchymal transition. RKIP levels in human colorectal cancer positively correlate with GSK3β expression. These findings reveal the RKIP/GSK3 axis as both a potential therapeutic target and a prognosis-based predictor of cancer progression.

Raf kinase inhibitor protein: mechanism of loss of expression and association with genomic instability.

Aims: Raf kinase inhibitory protein (RKIP; also known as PEBP, for phosphatidylethanolamine-binding protein) is an endogenous inhibitor of the Raf– MAPK kinase (MEK)–MAP kinase pathway. It has emerged as a significant metastasis suppressor in a variety of human cancers including colorectal cancer (CRC) and was recently shown to regulate the spindle checkpoint in cultured cells. This study aims at correlating RKIP expression with chromosomal instability in colorectal cancer samples and identifies possible mechanisms of RKIP loss. Methods: Chromosomal instability was assessed using metaphase-based comparative genomic hybridisation (CGH) and loss of heterozygosity (LOH) in 65 cases with microsatellite stable CRC and correlated with RKIP expression. Methyl-specific PCR was used on DNA extracted from 82 cases with CRC to determine CpG methylation status at the RKIP promoter and the results correlated with RKIP protein expression. Results: We demonstrate for the first time that in microsatellite stable (MSS) CRC, the number of chromosomal losses is inversely proportional to RKIP expression levels. We also show that methylation of the RKIP promoter is a major mechanism by which RKIP expression is silenced in CRC. Conclusions: RKIP loss by hypermethylation of its promoter could have a significant influence on colorectal cancer aneuploidy, which might explain its association with metastatic progression.

RKIP: much more than Raf kinase inhibitory protein.

From its discovery as a phosphatidylethanolamine‐binding protein in bovine brain to its designation as a physiological inhibitor of Raf kinase protein, RKIP has emerged as a critical molecule for maintaining subdued, well‐orchestrated cellular responses to stimuli. The disruption of RKIP in a wide range of pathologies, including cancer, Alzheimers disease, and pancreatitis, makes it an exciting target for individualized therapy and disease‐specific interventions. This review attempts to highlight recent advances in the RKIP field underscoring its potential role as a master modulator of many pivotal intracellular signaling cascades that control cellular growth, motility, apoptosis, genomic integrity, and therapeutic resistance. Specific biological and functional niches are highlighted to focus future research towards an enhanced understanding of the multiple roles of RKIP in health and disease. J. Cell. Physiol. 228: 1688–1702, 2013.

A defect in Nrf2 signaling constitutes a mechanism for cellular stress hypersensitivity in a genetic rat model of type 2 diabetes.

Nrf2 regulates the expression and coordinated induction of a battery of antioxidant phase 2 genes that protect cells against the cumulative damaging effects of oxidative stress (OS), a major contributor in the development of chronic diabetic complications. Using cultured dermal fibroblasts from rats with type 2 diabetes (DFs), we investigated the intracellular redox status and the adaptive response to OS, in which Nrf2 plays a central role. Our data confirmed that the generation of superoxide by NADPH oxidase and the mitochondria was enhanced in DFs compared with corresponding controls. This was associated with a decrease in the antioxidant capacity and an increase in the sensitivity of these DFs to hydrogen peroxide-induced necrotic cell death. Nrf2 levels in total cell extracts were diminished, and this abnormality appears to stem from a diabetes-related decrease in Nrf2 protein stability. Endogenous (oligomycin) and exogenous (tert-butylhydroquinone) induction of OS enhanced the nuclear translocation of Nrf2 and increased the mRNA expression of Nrf2-sensitive genes in control but not DFs. The activity of the GSK-3β/Fyn axis was increased markedly in DFs when compared with the corresponding controls. Chemical inhibition of GSK-3β mitigated the diabetes-related suppression of the OS-induced nuclear accumulation of Nrf2 and the transcriptional activation of the genes downstream of Nrf2. Overall, these findings suggest that an augmentation in GSK-3β/Fyn signaling during diabetes contributes to a deficit in both the cellular redox state and the Nrf2-based adaptive response to OS. Moreover, they may also offer a new perspective in the understanding and treatment of nonhealing diabetic wounds.

Inflammation and apoptosis in aortic tissues of aged type II diabetes: Amelioration with α-lipoic acid through phosphatidylinositol 3-kinase/Akt- dependent mechanism

AIMS Endothelial dysfunction is a key triggering event in the development of cardiovascular diseases and the current study explored this phenomenon in the context of inflammation, apoptosis, reactive oxygen species (ROS) and the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway during chronic diabetes. MAIN METHODS alpha-Lipoic acid (ALA) and wortmannin (WM) were chronically administered to aged Goto Kakizaki (GK) rats, a genetic model of non-obese type II diabetes. Key indices of inflammation, apoptosis and oxidative stress were assessed using western blotting, real-time PCR and immunofluoresence-based techniques. KEY FINDINGS A chronic inflammation (e.g., increased mRNA/protein levels of TNF-alpha, ICAM, fractalkine, CD-68, myeloperoxidase) in connection with increased caspase-based apoptotic cell death and heightened state of oxidative stress (HSOS)- appear to exist in diabetic cardiovascular tissues. An assessment of NF-kappaB dynamics in aged diabetic vessels revealed not only a marked increase in cytosolic phosphorylated levels of IkappaB-alpha, NIK, IKK but also an enhancement in nuclear localization of p65 concomitantly with augmented NF-kappaB-DNA binding activity. Most of the aforementioned cardiovascular-based diabetic abnormalities including reduced activities of PI3K and Akt kinase were ameliorated following chronic ALA therapy. WM, given to GK rats negated the anti-inflammatory and anti-apoptotic actions of ALA. SIGNIFICANCE Our data highlight a unifying mechanism whereby HSOS through an induction of NF-kappaB activity together with an impairment in PI3K/Akt pathway favors pro-inflammatory/pro-apoptotic diabetic vascular milieu that culminate in the onset of endothelial dysfunction, a phenomenon which appears to be amenable to treatment with antioxidants and/or PI3/Akt mimetics (e.g., ALA).

Diabetes-induced suppression of IGF-1 and its receptor mRNA levels in rat superior cervical ganglia

Insulin-like growth factor-I (IGF-I) is implicated in the development, survival and maintenance of function of sympathetic and sensory neurons. These neurons are affected at an early stage during the course of diabetes. Reverse transcriptase polymerase chain reaction (RT-PCR) based assay revealed that rat superior cervical ganglia (SCG) express mRNA transcripts for IGF-I and its receptor. Moreover, specific membrane protein binding sites for IGF-I within the SCG have also been demonstrated using competition-inhibition and affinity cross-linking techniques. An induction of diabetes with streptozotocin (STZ, 55 mg/kg, i.v.) produced a marked decrease in the SCG levels of mRNA transcripts for IGF-I and its receptor. Concentrations of circulating IGF-I and its receptor protein within the SCG were also reduced in this disease state. Insulin treatment partially prevented diabetes-related alterations in circulating IGF-I and the SCG-IGF-I system. Overall, the data described in this study may be of value in understanding the pathogenetic mechanism(s) responsible for the development of diabetic sympathetic neuropathy.

Heat-shock protein 72/73 and impaired wound healing in diabetic and hypercortisolemic states.

BACKGROUND Impaired wound healing is a well-documented phenomenon in experimental and clinical diabetes. Emerging evidence favors the involvement of glucocorticoids (GCs) in the pathogenesis of this diabetic complication. Recent data indicated that a heat-shock protein (HSP) with a molecular weight of about 70 kd is expressed in wound healing and it is under the control of the hypothalamic-pituitary-adrenal axis. In view of these findings, the current study was designed to examine the influence of diabetes and the hypercortisolemic state on the expression of HSP 72/73 during wound healing. METHODS Induction of diabetes was achieved by the intravenous injection of streptozotocin at a dose of 55 mg/kg. Subcutaneously implanted polyvinyl alcohol (PVA) sponges were used as a wound healing model. Control and diabetic animals received, respectively, subcutaneous 30-day timed-release pellets of GC (200 mg) and RU 486 (25 mg). Corresponding animals received placebo pellets. Expression of HSP 72/73 within the PVA sponges was assayed with use of Western blotting and immunohistochemical techniques. RESULTS GCs caused a Cushing-like syndrome with weight loss and adrenal atrophy. A pronounced accumulation of constitutive HSP 72/73 was observed in the cytoplasm of various cell types including fibroblasts, macrophages, and endothelium of nondiabetic controls. The PVA sponge contents of HSP 72/73 were decreased as a function of diabetes. A similar phenomenon was seen in control animals receiving high doses of GCs. Partial normalization of the associated hyperglycemic and hypercortisolemic states of diabetes with insulin (hyperglycemia) and the GC receptor block RU 486 (hypercortisolemia) ameliorated the diabetes-related decrease in PVA sponge contents of HSP 72/73. CONCLUSIONS The current study provides evidence that both diabetes and the hypercortisolemic state are associated with a reduction in PVA sponge content of HSP 72/73. An amelioration of these changes was achieved by the institution of RU 486 therapy. Although our data may point to the possibility that the diabetes-related decrease in HSP 72/73 is mediated at least in part by GCs, a confirmation regarding this premise awaits further investigation.

A New Model for Raf Kinase Inhibitory Protein Induced Chemotherapeutic Resistance

Therapeutic resistance remains the most challenging aspect of treating cancer. Raf kinase inhibitory protein (RKIP) emerged as a molecule capable of sensitizing cancerous cells to radio- and chemotherapy. Moreover, this small evolutionary conserved molecule, endows significant resistance to cancer therapy when its expression is reduced or lost. RKIP has been shown to inhibit the Raf-MEK-ERK, NFκB, GRK and activate the GSK3β signaling pathways. Inhibition of Raf-MEK-ERK and NFκB remains the most prominent pathways implicated in the sensitization of cells to therapeutic drugs. Our purpose was to identify a possible link between RKIP-KEAP 1-NRF2 and drug resistance. To that end, RKIP-KEAP 1 association was tested in human colorectal cancer tissues using immunohistochemistry. RKIP miRNA silencing and its inducible overexpression were employed in HEK-293 immortalized cells, HT29 and HCT116 colon cancer cell lines to further investigate our aim. We show that RKIP enhanced Kelch-like ECH-associated protein1 (KEAP 1) stability in colorectal cancer tissues and HT29 CRC cell line. RKIP silencing in immortalized HEK-293 cells (termed HEK-499) correlated significantly with KEAP 1 protein degradation and subsequent NRF2 addiction in these cells. Moreover, RKIP depletion in HEK-499, compared to control cells, bestowed resistance to supra physiological levels of H2O2 and Cisplatin possibly by upregulating NF-E2-related nuclear factor 2 (NRF2) responsive genes. Similarly, we observed a direct correlation between the extent of apoptosis, after treatment with Adriamycin, and the expression levels of RKIP/KEAP 1 in HT29 but not in HCT116 CRC cells. Our data illuminate, for the first time, the NRF2-KEAP 1 pathway as a possible target for personalized therapeutic intervention in RKIP depleted cancers.

ROS constitute a convergence nexus in the development of IGF1 resistance and impaired wound healing in a rat model of type 2 diabetes

SUMMARY An indolent non-healing wound and insulin and/or insulin-like growth factor (IGF1) resistance are cardinal features of diabetes, inflammation and hypercortisolemia. Little is known about why these phenomena occur in so many contexts. Do the various triggers that induce insulin and/or IGF1 resistance and retard wound healing act through a common mechanism? Cultured dermal fibroblasts from rats and full-thickness excisional wounds were used as models to test the premise that reactive oxygen species (ROS) play a causal role in the development of IGF1 resistance and impaired wound healing under different but pathophysiologically relevant clinical settings, including diabetes, dexamethasone-induced hypercortisolemia and TNFα-induced inflammation. In normal fibroblasts, IGF1 initiated a strong degree of phosphorylation of insulin receptor substrate 1 (IRS1) (Tyr612) and Akt (Ser473), concomitantly with increased PI3K activity. This phenomenon seemed to be attenuated in fibroblasts that had phenotypic features of diabetes, inflammation or hypercortisolemia. Notably, these cells also exhibited an increase in the activity of the ROS–phospho-JNK (p-JNK)–p-IRS1 (Ser307) axis. The above-mentioned defects were reflected functionally by attenuation in IGF1-dependent stimulation of key fibroblast functions, including collagen synthesis and cell proliferation, migration and contraction. The effects of IGF1 on glucose disposal and cutaneous wound healing were also impaired in diabetic or hypercortisolemic rats. The ROS suppressors EUK-134 and α-lipoic acid, or small interfering RNA (siRNA)-mediated silencing of JNK expression, restored IGF1 sensitivity both in vitro and in vivo, and also ameliorated the impairment in IGF1-mediated wound responses during diabetes, inflammation and hypercortisolemia. Our data advance the notion that ROS constitute a convergence nexus for the development of IGF1 resistance and impaired wound healing under different but pathophysiologically relevant clinical settings, with a proof of concept for the beneficial effect of ROS suppressors.

Metastatic recurrence of early-stage colorectal cancer is linked to loss of heterozygosity on chromosomes 4 and 14q

Objective: To investigate the prognostic value for loss of heterozygosity (LOH) of chromosomes 4 and 14q in early-stage colorectal cancer (CRC). Methods: A total of 70, largely microsatellite stable, tumours and their corresponding normal mucosa were subjected to microdissection and analysed for LOH at chromosomes 4 and 14q by using 13 highly polymorphic microsatellite markers. LOH was correlated with the survival of the patients, using univariate, multivariate and Kaplan–Meier’s survival curves. Result: LOH at D4S2935, D4S1579 and D4S1595 on chromosome 4 was significantly associated with metastatic recurrence of early-stage CRC. For chromosome arm 14q, two minimal regions of deletion were associated with metastatic recurrence and mapped to neighbouring markers D14S275/D14S49 at 14q12–13 and D14S65/D14S250 at 14q32. High-level loss (loss of five to eight of the informative microsatellite markers) on both chromosomes 4 and 14q, to be an independent prognostic indicator in early-stage CRC was shown by multivariate analysis. Conclusion: Determining the LOH of chromosomes 4 and 14q and their extent in primary tumours of patients with early-stage CRC may constitute a molecular signature of metastatic recurrence. This may be achieved if new finding sheds light on the treatment of this subgroup of patients that have been largely ignored.