PI3K/AKT signaling is known to regulate cancer metabolism, but whether metabolic feedback regulates the PI3K/AKT pathway is unclear. Here, we demonstrate the important reciprocal crosstalk between the PI3K/AKT signal and pentose phosphate pathway (PPP) branching metabolic pathways. PI3K/AKT activation stabilizes G6PD, the rate-limiting enzyme of the PPP, by inhibiting the newly identified E3 ligase TIRM21 and promotes the PPP. PPP metabolites, in turn, reinforce AKT activation and further promote cancer metabolic reprogramming by blocking the expression of the AKT inhibitor PHLDA3. Knockout of TRIM21 or PHLDA3 promotes crosstalk and cell proliferation. Importantly, PTEN null human cancer cells and in vivo murine models are sensitive to anti-PPP treatments, suggesting the importance of the PPP in maintaining AKT activation even in the presence of a constitutively activated PI3K pathway. Our study suggests that blockade of this reciprocal crosstalk mechanism may have a therapeutic benefit for cancers with PTEN loss or PI3K/AKT activation.

Prior studies have shown that during and after slow compressions of monomolecular films containing the complete set of purified phospholipids (PPL) from calf surfactant at an air/water interface, surface pressures (pi) reach and sustain values that are remarkably high relative to expectations from simple systems with model lipids. Microscopy shows that the liquid-expanded, tilted-condensed, and collapsed phases are present together in the PPL films between 45 and 65 mN/m. The Gibbs phase rule restricts equilibrium coexistence of three phases to a single pi for films with two components but not for more constituents. We therefore determined if the surprising stability of PPL reflects release from the thermodynamic restrictions of simple model systems by the presence of multiple components. Experiments with binary films containing dioleoyl phosphatidylcholine and dipalmitoyl phosphatidylcholine first tested the predictions of the phase rule. The onset of three-phase coexistence, determined by fluorescence microscopy, and its termination, established by relaxation of collapsing films on a captive bubble, occurred at similar pi. Experiments for PPL using the same methods suggested that the three phases might coexist over a range of pi, but limited to approximately 2 mN/m, and extending below rather than above the coexistence pi for the binary films. Our results show that the PPL films at high pi must deviate from equilibrium and that they must then be metastable.

Yan W, Biswas SC, Laderas TG, Hall SB. The melting of pulmonary surfactant monolayers. J Appl Physiol 102: 1739 -1745, 2007. First published December 28, 2006; doi:10.1152/japplphysiol.00948.2006.-Monomolecular films of phospholipids in the liquid-expanded (LE) phase after supercompression to high surface pressures (), well above the equilibrium surface pressure ( e) at which fluid films collapse from the interface to form a three-dimensional bulk phase, and in the tiltedcondensed (TC) phase both replicate the resistance to collapse that is characteristic of alveolar films in the lungs. To provide the basis for determining which film is present in the alveolus, we measured the melting characteristics of monolayers containing TC dipalmitoyl phosphatidylcholine (DPPC), as well as supercompressed 1-palmitoyl-2-oleoyl phosphatidylcholine and calf lung surfactant extract (CLSE). Films generated by appropriate manipulations on a captive bubble were heated from Յ27°C to Ն60°C at different constant above e. DPPC showed the abrupt expansion expected for the TC-LE phase transition, followed by the contraction produced by collapse. Supercompressed CLSE showed no evidence of the TC-LE expansion, arguing that supercompression did not simply convert the mixed lipid film to TC DPPC. For both DPPC and CLSE, the melting point, taken as the temperature at which collapse began, increased at higher , in contrast to 1-palmitoyl-2-oleoyl phosphatidylcholine, for which higher produced collapse at lower temperatures. For between 50 and 65 mN/m, DPPC melted at 48 -55°C, well above the main transition for bilayers at 41°C. At each , CLSE melted at temperatures Ͼ10°C lower. The distinct melting points for TC DPPC and supercompressed CLSE provide the basis by which the nature of the alveolar film might be determined from the temperature-dependence of pulmonary mechanics. captive bubble; dipalmitoyl phosphatidylcholine; jammed; monolayer; pulmonary mechanics; supercompressed THE BEHAVIOR OF PULMONARY surfactant indicates that films at the air/water interface in the alveoli are solid. Multiple approaches consistently indicate that, when compressed by the decreasing alveolar surface area during exhalation, the films of pulmonary surfactant reach high surface pressures () (13,19,30,35,37,39). The observed values are well above the equilibrium spreading pressure ( e ) of ϳ46 mN/m, at which two-dimensional monomolecular films coexist at equilibrium with their three-dimensional bulk phases (14). Films under equilibrium conditions never reach Ͼ e , because compression produces only flow of constituents into the bulk phase, with no increase in the density of material within the interface. The Ͼ e observed in static lungs, therefore, indicate that the alveolar films deviate from equilibrium and must by definition be metastable. The rate at which a film flows into the bulk phase in response to the thermodynamic driving force of ( Ϫ e ) can be used to calculate an effective viscosity (27). The very slow rates at which films in the lungs undergo this p...

Combining immune checkpoint therapy (ICT) and targeted therapy holds great promises for broad and long-lasting anti-cancer therapies. However, combining ICT with anti-PI3K inhibitors have been challenging because the multifaceted effects of PI3K on both cancer cells and immune cells within the tumor microenvironment. Here we find that intermittent but not daily dosing of a PI3Kα/β/δ inhibitor, BAY1082439, on Pten-null prostate cancer models could overcome ICT resistance and unleash CD8+ T cell-dependent anti-tumor immunity in vivo. Mechanistically, BAY1082439 converts cancer cell-intrinsic immune-suppression to immune-stimulation by promoting IFNα/IFNγ pathway activation, β2-microglubin expression and CXCL10/CCL5 secretion. With its preferential regulatory T cell inhibition activity, BAY1082439 promotes clonal expansion of tumor-associated CD8+ T cells, most likely via tertiary lymphoid structures. Once primed, tumors remain T cell-inflamed, become responsive to anti-PD-1 therapy and have durable therapeutic effect. Our data suggest that intermittent PI3K inhibition can alleviate Pten-null cancer cell-intrinsic immunosuppressive activity and turn “cold” tumors into T cell-inflamed ones, paving the way for successful ICT.