Therapeutic implications of cancer stem cells

Most cancers comprise a heterogenous population of cells with marked differences in their proliferative potential as well as the ability to reconstitute the tumor upon transplantation. Cancer stem cells are a minor population of tumor cells that possess the stem cell property of self-renewal. In addition, dysregulation of stem cell self-renewal is a likely requirement for the development of cancer. This new model for cancer will have significant ramifications for the way we study and treat cancer. In addition, through targeting the cancer stem cell and its dysregulated self-renewal, our therapies for treating cancer are likely to improve.     

Therapeutic siRNA silencing in inflammatory monocytes in mice

Excessive and prolonged activity of inflammatory monocytes is a hallmark of many diseases with an inflammatory component. In such conditions, precise targeting of these cells could be therapeutically beneficial while sparing many essential functions of the innate immune system, thus limiting unwanted effects. Inflammatory monocytes-but not the noninflammatory subset-depend on the chemokine receptor CCR2 for localization to injured tissue. Here we present an optimized lipid nanoparticle and a CCR2-silencing short interfering RNA that, when administered systemically in mice, show rapid blood clearance, accumulate in spleen and bone marrow, and localize to monocytes. Efficient degradation of CCR2 mRNA in monocytes prevents their accumulation in sites of inflammation. Specifically, the treatment attenuates their number in atherosclerotic plaques, reduces infarct size after coronary artery occlusion, prolongs normoglycemia in diabetic mice after pancreatic islet transplantation, and results in reduced tumor volumes and lower numbers of tumor-associated macrophages.     

Enhancing chemotherapy response with Bmi-1 silencing in ovarian cancer

Undoubtedly ovarian cancer is a vexing, incurable disease for patients with recurrent cancer and therapeutic options are limited. Although the polycomb group gene, Bmi-1 that regulates the self-renewal of normal stem and progenitor cells has been implicated in the pathogenesis of many human malignancies, yet a role for Bmi-1 in influencing chemotherapy response has not been addressed before. Here we demonstrate that silencing Bmi-1 reduces intracellular GSH levels and thereby sensitizes chemoresistant ovarian cancer cells to chemotherapeutics such as cisplatin. By exacerbating ROS production in response to cisplatin, Bmi-1 silencing activates the DNA damage response pathway, caspases and cleaves PARP resulting in the induction apoptosis in ovarian cancer cells. In an in vivo orthotopic mouse model of chemoresistant ovarian cancer, knockdown of Bmi-1 by nanoliposomal delivery significantly inhibits tumor growth. While cisplatin monotherapy was inactive, combination of Bmi-1 silencing along with cisplatin almost completely abrogated ovarian tumor growth. Collectively these findings establish Bmi-1 as an important new target for therapy in chemoresistant ovarian cancer.     

Therapeutic implications of osteoprotegerin

Osteoprotegerin (OPG), a member of the tumor necrosis factor (TNF) receptor superfamily, contributes determinatively to the bone remodeling as well as to the pathogenetic mechanism of bone malignancies and disorders of mineral metabolism. There is additional evidence that OPG can promote cell survival by inhibiting TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. A number of recent in vitro, in vivo and clinical studies have defined the role of the RANK/RANKL/OPG pathway in skeletal and vascular diseases. These works were the milestone of the deep understanding of the mechanism of OPG. This review provides an overview of the potential innovative therapeutic strategies of OPG in metastatic breast and prostate carcinoma, multiple myeloma, postmenopausal osteoporosis, glucocorticoid-induced osteoporosis and rheumatoid arthritis. Special reference is given to the increasing evidence that RANKL and OPG may link the skeletal with the vascular system.     

Targeting cyclooxygenases-1 and -2 in neuroinflammation: Therapeutic implications

Neuroinflammation has been implicated in the pathogenesis or the progression of a variety of acute and chronic neurological and neurodegenerative disorders, including Alzheimer’s disease. Prostaglandin H synthases or cyclooxygenases (COX -1 and COX-2) play a central role in the inflammatory cascade by converting arachidonic acid into bioactive prostanoids. In this review, we highlighted recent experimental data that challenge the classical view that the inducible isoform COX-2 is the most appropriate target to treat neuroinflammation. First, we discuss data showing that COX-2 activity is linked to anti-inflammatory and neuroprotective actions and is involved in the generation of novel lipid mediators with pro-resolution properties. Then, we review recent data demonstrating that COX-1, classically viewed as the homeostatic isoform, is actively involved in brain injury induced by pro-inflammatory stimuli including Aβ, lipopolysaccharide, IL-1β, and TNF-α. Overall, we suggest revisiting the traditional views on the roles of each COX during neuroinflammation and we propose COX-1 inhibition as a viable therapeutic approach to treat CNS diseases with a marked inflammatory component.     

Aberrant silencing of the endocrine peptide gene tachykinin-1 in gastric cancer

Tachykinin-1 (TAC1) is the precursor protein for neuroendocrine peptides, including substance P, and is centrally involved in gastric secretion, motility, mucosal immunity, and cell proliferation. Here we report aberrant silencing of TAC1 in gastric cancer (GC) by promoter hypermethylation. TAC1 methylation and mRNA expression in 47 primary GCs and 41 noncancerous gastric mucosae (NLs) were analyzed by utilizing real-time quantitative PCR-based assays. TAC1 methylation was more prevalent in GCs than in NLs: 21 (45%) of 47 GCs versus 6 (15%) of 41 NLs (p < 0.01). Microsatellite instability was also associated with TAC1 methylation in GCs. There was no significant association between TAC1 methylation and age, gender, stage, histological differentiation, or the presence of Helicobacter pylori. TAC1 mRNA was markedly downregulated in GCs relative to NLs. 5-Aza-2′-deoxycytidine-induced demethylation of the TAC1 promoter resulted in TAC1 mRNA upregulation. Further studies are indicated to elucidate the functional involvement of TAC1 in gastric carcinogenesis.     

Sphingosine-1-phosphate lyase in immunity and cancer: silencing the siren

Sphingosine-1-phosphate (S1P) is a bioactive lipid that promotes cell survival, proliferation and migration, platelet aggregation, mediates ischemic preconditioning, and is essential for angiogenesis and lymphocyte trafficking. Sphingosine-1-phosphate lyase (SPL) is the enzyme responsible for the irreversible degradation of S1P and is, thus, in a strategic position to regulate these same processes by removing available S1P signaling pools, that is, silencing the siren. In fact, recent studies have implicated SPL in the regulation of immunity, cancer surveillance and other physiological processes. Here, we summarize the current understanding of SPL function and regulation, and discuss how SPL might facilitate cancer chemoprevention and serve as a target for modulation of immune responses in transplantation settings and in the treatment of autoimmune disease.     

GIPC participates in G protein signaling downstream of insulin-like growth factor 1 receptor.

Several recent studies have demonstrated that insulin-like growth factor (IGF)-1-induced mitogen-activated protein kinase (MAP kinase) activation is abolished by pertussis toxin, suggesting that trimeric G proteins of the G(i) class are novel cellular targets of the IGF-1 signaling pathway. We report here that the intracellular domain of the Xenopus IGF-1 receptor is capable of binding to the Xenopus homolog of mammalian GIPC, a PDZ domain-containing protein previously identified as a binding partner of G(i)-specific GAP (RGS-GAIP). Binding of xGIPC to xIGF-1 receptor is independent of the kinase activity of the receptor and appears to require the PDZ domain of xGIPC. Injection of two C-terminal truncation mutants that retained the PDZ domain blocked IGF-1-induced Xenopus MAP kinase activation and oocyte maturation. While full-length xGIPC injection did not significantly alter insulin response, it greatly enhanced human RGS-GAIP in stimulating the insulin response in frog oocytes. This represents the first demonstration that GIPC x RGS-GAIP complex acts positively in IGF-1 receptor signal transduction.     

Ambra1 in cancer: implications for clinical oncology

Apoptosis - Activating molecule in Beclin-1-regulated autophagy protein 1 (Ambra1) is well known to mediate the autophagy process and promote the formation of autophagosomes. In addition, Ambra1 is...     

GIPC蛋白与肿瘤发生机制研究进展

GIPC蛋白即G蛋白信号调节体-G alpha相互作用蛋白C端,在蛋白流动、胞吞作用和受体聚集方面发挥重要作用。同时,GIPC蛋白在肿瘤发生中发挥重要的调节机制,可能是一个新的肿瘤相关抗原和治疗靶点。有关GIPC蛋白的研究近年在国际上形成了一个新的热点。我们以GIPC蛋白与肿瘤发生机制为重点,简要综述国内外关于该蛋白的研究现状。     

Chemically modified peptides targeting the PDZ domain of GIPC as a therapeutic approach for cancer

GIPC (GAIP-interacting protein, C terminus) represents a new target class for the discovery of chemotherapeutics. While many of the current generation of anticancer agents function by directly binding to intracellular kinases or cell surface receptors, the disruption of cytosolic protein-protein interactions mediated by non-enzymatic domains is an underdeveloped avenue for inhibiting cancer growth. One such example is the PDZ domain of GIPC. Previously we developed a molecular probe, the cell-permeable octapeptide CR1023 (N-myristoyl-PSQSSSEA), which diminished proliferation of pancreatic cancer cells. We have expanded upon that discovery using a chemical modification approach and here report a series of cell-permeable, side chain-modified lipopeptides that target the GIPC PDZ domain in vitro and in vivo. These peptides exhibit significant activity against pancreatic and breast cancers, both in cellular and animal models. CR1166 (N-myristoyl-PSQSK(εN-4-bromobenzoyl)SK(εN-4-bromobenzoyl)A), bearing two halogenated aromatic units on alternate side chains, was found to be the most active compound, with pronounced down-regulation of EGFR/1GF-1R expression. We hypothesize that these organic acid-modified residues extend the productive reach of the peptide beyond the canonical binding pocket, which defines the limit of accessibility for the native proteinogenic sequences that the PDZ domain has evolved to recognize. Cell permeability is achieved with N-terminal lipidation using myristate, rather than a larger CPP (cell-penetrating peptide) sequence. This, in conjunction with optimization of targeting through side chain modification, has yielded an approach that will allow the discovery and development of next-generation cellular probes for GIPC PDZ as well as for other PDZ domains.     

MicroRNAs and other small silencing RNAs in cancer

Small noncoding RNAs are key controllers of cellular function, and their deregulation can lead to cancer development and metastatic evolution. This review summarizes the most important examples of small RNAs involved in human cancer and discusses their clinical use as biomarkers and drug targets for diagnosis, prognosis, and treatment of cancer. We also describe the possible mechanisms underlying small RNA-mediated transformation and outline the future describing new small RNA families with great potential in cancer biology.     

Multiple implications of 3-phosphoinositide-dependent protein kinase 1 in human cancer

3-phosphoinositide-dependent protein kinase-1 (PDK1) is a central mediator of cellular signaling between phosphoinositide-3 kinase and various intracellular serine/threonine kinases, including protein kinase B, p70 ribosomal S6 kinase, serum and glucocorticoid-inducible kinase, and protein kinase C. PDK1 activates members of the AGC family of protein kinases by phosphorylating serine/threonine residues in the activation loop. Here, we review the regulatory mechanisms of PDK1 and its roles in cancer. PDK1 is activated by autophosphorylation in the activation loop and other serine residues, as well as by phosphorylation of Tyr-9 and Tyr-373/376. Src appears to recognize PDK1 following tyrosine phosphorylation. The role of heat shock protein 90 in regulating PDK1 stability and PDK1-Src complex formation are also discussed. Furthermore, we summarize the subcellular distribution of PDK1. Finally, an important role for PDK1 in cancer chemotherapy is proposed. In conclusion, a better understanding of its molecular regulatory mechanisms in various signaling pathways will help to explain how PDK1 acts as an oncogenic kinase in various cancers, and will contribute to the development of novel cancer chemotherapies.     

A GIPC1-Palmitate Switch Modulates Dopamine Drd3 Receptor Trafficking and Signaling

Palmitoylation is involved in several neuropsychiatric and movement disorders for which a dysfunctional signaling of the dopamine D3 receptor (Drd3) is hypothesized. Computational modeling of Drd3''s homologue, Drd2, has shed some light on the putative role of palmitoylation as a reversible switch for dopaminergic receptor signaling. Drd3 is presumed to be palmitoylated, based on sequence homology with Drd2, but the functional attributes afforded by Drd3 palmitoylation have not been studied. Since these receptors are major targets of antipsychotic and anti-Parkinsonian drugs, a better characterization of Drd3 signaling and posttranslational modifications, like palmitoylation, may improve the prospects for drug development. Using molecular dynamics simulations, we evaluated in silico how Drd3 palmitoylation could elicit significant remodeling of the C-terminal cytoplasmic domain to expose docking sites for signaling proteins. We tested this model in cellulo by using the interaction of Drd3 with the G-alpha interacting protein (GAIP) C terminus 1 (GIPC1) as a template. From a series of biochemical studies, live imaging, and analyses of mutant proteins, we propose that Drd3 palmitoylation acts as a molecular switch for Drd3-biased signaling via a GIPC1-dependent route, which is likely to affect the mode of action of antipsychotic drugs.     

Epigenetic silencing of the MGMT gene in cancer.

Silencing of the O6-methylguanine-DNA methyltransferase (MGMT) gene, a key to DNA repair, plays a critical role in the development of cancer. The gene product, functioning normally, removes a methyl group from mutagenic O6-methylguanine, which is produced by alkylating agents and can make a mismatched pair with thymine, leading to transition mutation through DNA replication. MGMT is epigenetically silenced in various human tumors. It is well known that DNA hypermethylation at the promoter CpG island plays a pivotal role in the epigenetic silencing of tumor suppressor genes. MGMT silencing, however, occurs without DNA hypermethylation in some cancer cells. Dimethylation of histone H3 lysine 9 and binding of methyl-CpG binding proteins are common and essential in MGMT-silenced cells. Silencing of MGMT has been shown to be a poor prognostic factor but a good predictive marker for chemotherapy when alkylating agents are used. In this review, we describe recent advances in understanding the silencing of MGMT and its role in carcinogenesis; epigenetic mechanisms; and clinical implications.