Pleckstrin homology domain of Akt kinase: a proof of principle for highly specific and effective non-enzymatic anti-cancer target

Two cooperative lipid binding sites within the pleckstrin homology domain are necessary for AKT binding and stabilization to the plasma membrane

Almost four decades after the identification of the AKT protein and understanding of its role in cancer, barriers remain in the translation of AKT inhibitors for clinical applications. Here, we provide new molecular insight into the first step of AKT activation where AKT binds to the plasma membrane and its orientation is stabilized in a bilayer with lateral heterogeneity (Lo-Ld phase coexistence). We have applied molecular dynamic simulations and molecular and cell biology approaches, and demonstrate that AKT recruitment to the membrane requires a second binding site in the AKT pleckstrin homology (PH) domain that acts cooperatively with the known canonical binding site. Given the precision with which we have identified the protein-lipid interactions, the study offers new directions for AKT-targeted therapy and for testing small molecules to target these specific amino acid-PIP molecular bonds.

Encapsulation of Inositol Hexakisphosphate with Chitosan via Gelation to Facilitate Cellular Delivery and Programmed Cell Death in Human Breast Cancer Cells

Inositol hexakisphosphate (InsP6) is the most abundant inositol polyphosphate both in plant and animal cells. Exogenous InsP6 is known to inhibit cell proliferation and induce apoptosis in cancerous cells. However, cellular entry of exogenous InsP6 is hindered due to the presence of highly negative charge on this molecule. Therefore, to enhance the cellular delivery of InsP6 in cancerous cells, InsP6 was encapsulated by chitosan (CS), a natural polysaccharide, via the ionic gelation method. Our hypothesis is that encapsulated InsP6 will enter the cell more efficiently to trigger its apoptotic effects. The incorporation of InsP6 into CS was optimized by varying the ratios of the two and confirmed by InsP6 analysis via polyacrylamide gel electrophoresis (PAGE) and atomic absorption spectrophotometry (AAS). The complex was further characterized by Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) for physicochemical changes. The data indicated morphological changes and changes in the spectral properties of the complex upon encapsulation. The encapsulated InsP6 enters human breast cancer MCF-7 cells more efficiently than free InsP6 and triggers apoptosis via a mechanism involving the production of reactive oxygen species (ROS). This work has potential for developing cancer therapeutic applications utilizing natural compounds that are likely to overcome the severe toxic effects associated with synthetic chemotherapeutic drugs.

Lancemaside A Isolated from the Root of Codonopsis lanceolata Inhibits Ovarian Cancer Cell Invasion via the Reactive Oxygen Species (ROS)-Mediated p38 Pathway

Codonopsis lanceolata roots have been widely used in Korean cuisine and traditional medicine. This study aimed to investigate the antimetastatic effects of lancemaside A, a major triterpenoid saponin, isolated from the roots of C. lanceolata, in human ovarian cancer cells. Lancemaside A significantly suppressed the migration and invasion and the expression of matrix metalloproteinases (MMPs)-2 and -9 in ovarian cancer A2780 and SKOV3 cells. Treatment with lancemaside A generated reactive oxygen species (ROS) in ovarian cancer cells. However, treatment with anti-oxidant N-acetyl-L-cysteine (NAC) significantly negated the anti-invasive activity of lancemaside A. Additionally, lancemaside A activated p38 MAP kinase, which is mediated by ROS generation. This is the first study, to our knowledge, to reveal that lancemaside A isolated from the roots of C. lanceolata exerts antimetastatic activity through inhibition of MMP expression and cancer cell invasion via activation of the ROS-mediated p38 pathway.

Discovery of Small Molecules That Target the Phosphatidylinositol (3,4,5) Trisphosphate (PIP3)-Dependent Rac Exchanger 1 (P-Rex1) PIP3-Binding Site and Inhibit P-Rex1-Dependent Functions in Neutrophils

Phosphatidylinositol (3,4,5) trisphosphate (PIP₃)-dependent Rac exchanger 1 (P-Rex1) is a Rho guanine-nucleotide exchange factor that was originally discovered in neutrophils and is regulated by G protein βγ subunits and the lipid PIP₃ in response to chemoattractants. P-Rex1 has also become increasingly recognized for its role in promoting metastasis of breast cancer, prostate cancer, and melanoma. Recent structural, biochemical, and biologic work has shown that binding of PIP₃ to the pleckstrin homology (PH) domain of P-Rex1 is required for its activation in cells. Here, differential scanning fluorimetry was used in a medium-throughput screen to identify six small molecules that interact with the P-Rex1 PH domain and block binding of and activation by PIP₃ Three of these compounds inhibit N-formylmethionyl-leucyl-phenylalanine induced spreading of human neutrophils as well as activation of the GTPase Rac2, both of which are downstream effects of P-Rex1 activity. Furthermore, one of these compounds reduces neutrophil velocity and inhibits neutrophil recruitment in response to inflammation in a zebrafish model. These results suggest that the PH domain of P-Rex1 is a tractable drug target and that these compounds might be useful for inhibiting P-Rex1 in other experimental contexts. SIGNIFICANCE STATEMENT: A set of small molecules identified in a thermal shift screen directed against the phosphatidylinositol (3,4,5) trisphosphate-dependent Rac exchanger 1 (P-Rex1) pleckstrin homology domain has effects consistent with P-Rex1 inhibition in neutrophils.

PH-domain-binding inhibitors of nucleotide exchange factor BRAG2 disrupt Arf GTPase signaling

Peripheral membrane proteins orchestrate many physiological and pathological processes, making regulation of their activities by small molecules highly desirable. However, they are often refractory to classical competitive inhibition. Here, we demonstrate that potent and selective inhibition of peripheral membrane proteins can be achieved by small molecules that target protein-membrane interactions by a noncompetitive mechanism. We show that the small molecule Bragsin inhibits BRAG2-mediated Arf GTPase activation in vitro in a manner that requires a membrane. In cells, Bragsin affects the trans-Golgi network in a BRAG2- and Arf-dependent manner. The crystal structure of the BRAG2-Bragsin complex and structure-activity relationship analysis reveal that Bragsin binds at the interface between the PH domain of BRAG2 and the lipid bilayer to render BRAG2 unable to activate lipidated Arf. Finally, Bragsin affects tumorsphere formation in breast cancer cell lines. Bragsin thus pioneers a novel class of drugs that function by altering protein-membrane interactions without disruption.

Chemical constituents of the roots of Codonopsis lanceolata

A new phenylpropanoid (1), a new alkaloid (11), and a new natural polyacetylene (17), together with nine phenolic compounds (2-10), five alkaloids (12-16), three polyacetylenes (18-20), three triterpenoidal saponins (21-23), one phenylethanoid glycoside (24), and three hexyl glycosides (25-27) with previous known structures, were isolated from the roots of Codonopsis lanceolata. All of the isolates 1-27 were evaluated for their inhibitory effects on LPS-induced nitric oxide (NO) production in RAW 264.7 macrophages and cell viability in A2780 human ovarian cancer cells. Among the isolates, lancemasides A and B have a significant inhibitory effect on the production of NO in RAW264.7 cells (IC₅₀ values < 50 μM). In A2780 cells, lancemaside A exhibited the most potent inhibitory effect on cell viability. This is the first report on the pharmacological activities of lancemaside B (22).

SMYD3-mediated lysine methylation in the PH domain is critical for activation of AKT1

AKT1 is a cytosolic serine/threonine kinase that is overexpressed in various types of cancer and has a central role in human tumorigenesis. Although it is known that AKT1 is post-translationally modified in various ways including phosphorylation and ubiquitination, methylation has not been reported so far. Here we demonstrate that the protein lysine methyltransferase SMYD3 methylates lysine 14 in the PH domain of AKT1 both in vitro and in vivo. Lysine 14-substituted AKT1 shows significantly lower levels of phosphorylation at threonine 308 than wild-type AKT1, and knockdown of SMYD3 as well as treatment with a SMYD3 inhibitor significantly attenuates this phosphorylation in cancer cells. Furthermore, substitution of lysine 14 diminishes the plasma membrane accumulation of AKT1, and cancer cells overexpressing lysine 14-substiuted AKT1 shows lower growth rate than those overexpressing wild-type AKT1. These results imply that SMYD3-mediated methylation of AKT1 at lysine 14 is essential for AKT1 activation and that SMYD3-mediated AKT1 methylation appears to be a good target for development of anti-cancer therapy.

Role of cytochrome P450 2J2 on cell proliferation and resistance to an anticancer agent in hepatocellular carcinoma HepG2 cells

The present study examined the role of human cytochrome P450 2J2 (CYP2J2) on cell proliferation and resistance to an anticancer agent using stable hepatocellular carcinoma HepG2 cells overexpressing CYP2J2. Overexpression of CYP2J2 significantly increased HepG2 cell proliferation and the expression levels of cell cycle regulatory proteins, including cyclin D1, cyclin E, cyclin-dependent kinase (Cdk)2 and Cdk4. CYP2J2-overexpressing HepG2 cells exhibited high levels of Akt phosphorylation compared with those observed in wild-type HepG2 cells. Although Akt phosphorylation in both cell lines was significantly attenuated by LY294002, a specific phosphoinositide 3-kinase/Akt signaling inhibitor, the levels of Akt phosphorylation following treatment with LY294002 were higher in CYP2J2-overexpressing HepG2 cells than in wild-type HepG2 cells. Cell counting revealed that proliferation was reduced by LY294002 in both cell lines; however, CYP2J2-overexpressing HepG2 cell numbers were higher than those of wild-type HepG2 cells following treatment with LY294002. These results indicated that increased cell proliferation by CYP2J2 overexpression is mediated by increased Akt activity. It was also demonstrated that doxorubicin, an anticancer agent, reduced cell viability, induced a significant increase in the B-cell lymphoma (Bcl)-2 associated X protein (Bax)/Bcl-2 ratio and decreased pro-caspase-3 levels in wild-type HepG2 cells. However, the doxorubicin-induced reduction in cell viability was significantly attenuated by enhanced upregulation of CYP2J2 expression. The increase in the Bax/Bcl-2 ratio and the decrease in pro-caspase-3 levels were also recovered by CYP2J2 overexpression. In conclusion, CYP2J2 serves important roles in cancer cell proliferation and resistance to the anticancer agent doxorubicin in HepG2 cells.

Membrane and Protein Interactions of the Pleckstrin Homology Domain Superfamily

The human genome encodes about 285 proteins that contain at least one annotated pleckstrin homology (PH) domain. As the first phosphoinositide binding module domain to be discovered, the PH domain recruits diverse protein architectures to cellular membranes. PH domains constitute one of the largest protein superfamilies, and have diverged to regulate many different signaling proteins and modules such as Dbl homology (DH) and Tec homology (TH) domains. The ligands of approximately 70 PH domains have been validated by binding assays and complexed structures, allowing meaningful extrapolation across the entire superfamily. Here the Membrane Optimal Docking Area (MODA) program is used at a genome-wide level to identify all membrane docking PH structures and map their lipid-binding determinants. In addition to the linear sequence motifs which are employed for phosphoinositide recognition, the three dimensional structural features that allow peripheral membrane domains to approach and insert into the bilayer are pinpointed and can be predicted ab initio. The analysis shows that conserved structural surfaces distinguish which PH domains associate with membrane from those that do not. Moreover, the results indicate that lipid-binding PH domains can be classified into different functional subgroups based on the type of membrane insertion elements they project towards the bilayer.