No abstract

The phosphoinositide 3-kinase (PI3K) pathway crucially controls metabolism and cell growth. Although different PI3K catalytic subunits are known to play distinct roles, the specific in vivo function of p110β (the product of the PIK3CB gene) is not clear. Here, we show that mouse mutants expressing a catalytically inactive PIK3CB K805R mutant survived to adulthood but showed growth retardation and developed mild insulin resistance with age. Pharmacological and genetic analyses of p110β function revealed that p110β catalytic activity is required for PI3K signaling downstream of heterotrimeric guanine nucleotide-binding (G protein)-coupled receptors as well as to sustain long term insulin signaling. In addition, PIK3CB K805R mice were protected in a model of ERBB2-driven tumor development. These findings indicate an unexpected role for p110β catalytic activity in diabetes and cancer, opening potential new avenues for therapeutic intervention.

Clinical studies have revealed that cancer patients whose tumours have increased ErbB2 expression tend to have more aggressive, metastatic disease, which is associated with parameters predicting a poor outcome. The molecular basis underlying ErbB2-dependent cell motility and metastases formation, however, still remains poorly understood. In this study, we show that activation of a set of signalling molecules, including MAPK, phosphatidylinositol-3-OH kinase (PI(3)K) and Src, is required for Neu/ErbB2-dependent lamellipodia formation and for motility of breast carcinoma cells. Stimulation of these molecules, however, failed to induce efficient cell migration in the absence of Neu/ErbB2 phosphorylation at Tyr 1201 or Tyr 1227. We describe a novel molecule, Memo (mediator of ErbB2-driven cell motility), that interacts with a phospho-Tyr 1227-containing peptide, most probably through the Shc adaptor protein. After Neu/ErbB2 activation, Memo-defective cells form actin fibres and grow lamellipodia, but fail to extend microtubules towards the cell cortex. Our data suggest that Memo controls cell migration by relaying extracellular chemotactic signals to the microtubule cytoskeleton.

Genomic alterations in GNAS, the gene coding for the Gαs heterotrimeric G-protein, are associated with a large number human of diseases. Here, we explored the role of Gαs on stem cell fate decisions by using the mouse epidermis as a model system. Conditional epidermal deletion of Gnas or repression of PKA signaling caused a remarkable expansion of the stem cell compartment, resulting in rapid basal cell carcinoma formation. In contrast, inducible expression of active Gαs in the epidermis caused hair follicle stem cell exhaustion and hair loss. Mechanistically, we found that Gαs-PKA disruption promotes the cell autonomous Sonic Hedgehog pathway stimulation and Hippo signaling inhibition, resulting in the non-canonical activation of GLI and YAP1. Our study highlights an important tumor suppressive function of Gαs-PKA, limiting the proliferation of epithelial stem cells and maintaining proper hair follicle homeostasis. These findings can have broad implications in multiple pathophysiological conditions, including cancer.

No abstract

Phosphoinositide 3-kinase (PI3K) is deregulated in a wide variety of human tumors and triggers activation of protein kinase B (PKB/Akt) and mammalian target of rapamycin (mTOR). Here we describe the preclinical characterization of compound 1 (PQR309, bimiralisib), a potent 4,6-dimorpholino-1,3,5-triazine-based pan-class I PI3K inhibitor, which targets mTOR kinase in a balanced fashion at higher concentrations. No off-target interactions were detected for 1 in a wide panel of protein kinase, enzyme, and receptor ligand assays. Moreover, 1 did not bind tubulin, which was observed for the structurally related 4 (BKM120, buparlisib). Compound 1 is orally available, crosses the blood-brain barrier, and displayed favorable pharmacokinetic parameters in mice, rats, and dogs. Compound 1 demonstrated efficiency in inhibiting proliferation in tumor cell lines and a rat xenograft model. This, together with the compound's safety profile, identifies 1 as a clinical candidate with a broad application range in oncology, including treatment of brain tumors or CNS metastasis. Compound 1 is currently in phase II clinical trials for advanced solid tumors and refractory lymphoma.

Phosphoinositide 3-kinase gamma (PI3Kgamma) plays a major role in chronic inflammation and allergy. It is a heterodimer of a catalytic p110gamma subunit and an adaptor protein, either p101 or the p101 homolog p84 (p87(PIKAP)). It is unclear whether both PI3Kgamma complexes specifically modulate responses such as chemotaxis and degranulation. In mast cells, the p84:p110gamma complex synergizes with immunoglobulin E (IgE)- and antigen-clustered FcepsilonRI receptor signaling and is required to achieve maximal degranulation. During this process, PI3Kgamma is activated by ligands of heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs), in particular adenosine receptors, through autocrine and paracrine pathways. Here, we show that p110gamma needs p84 to relay signals from GPCRs to formation of phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P(3)], phosphorylation of Akt, migration of cells, and synergistic adenosine-enforced degranulation. Furthermore, the absence of adaptor subunits could not be compensated for by increased p110gamma abundance. Differentiated, p110gamma null cells also lost adaptor proteins. Complementation of p110gamma null mast cells with p101 and p110gamma restored the activation of Akt and cell migration, but failed to support degranulation. Lack of degranulation was attributed to a change in the spatiotemporal localization of PI3Kgamma-derived PtdIns(3,4,5)P(3); although both p84:p110gamma and p101:p110gamma complexes initially deposited PtdIns(3,4,5)P(3) at the plasma membrane, p101:p110gamma-derived PtdIns(3,4,5)P(3) was rapidly endocytosed to motile, microtubule-associated vesicles. In addition, p84:p110gamma, but not p101:p110gamma signaling was sensitive to disruption of lipid rafts. Our results demonstrate a nonredundant function for the p101 and p84 PI3Kgamma adaptor proteins and show that distinct pools of PtdIns(3,4,5)P(3) at the plasma membrane can elicit specific cell responses.

Phosphoinositide 3-kinase (PI3K)/protein kinase B/Akt and Ras/mitogen-activated protein kinase pathways are often constitutively activated in melanoma and have thus been considered as promising drug targets. Exposure of melanoma cells to NVP-BAG956, NVP-BBD130, and NVP-BEZ235, a series of novel, potent, and stable dual PI3K/ mammalian target of rapamycin (mTOR) inhibitors, resulted in complete G1 growth arrest, reduction of cyclin D1, and increased levels of p27 KIP1 , but negligible apoptosis. In contrast, treatment of melanoma with the pan-class I PI3K inhibitor ZSTK474 or the mTORC1 inhibitor rapamycin resulted only in minor reduction of cell proliferation. In a syngeneic B16 mouse melanoma tumor model, orally administered NVP-BBD130 and NVP-BEZ235 efficiently attenuated tumor growth at primary and lymph node metastatic sites with no obvious toxicity. Metastatic melanoma in inhibitor-treated mice displayed reduced numbers of proliferating and significantly smaller tumor cells. In addition, neovascularization was blocked and tumoral necrosis increased when compared with vehicle-treated mice. In conclusion, compounds targeting PI3K and mTOR simultaneously were advantageous to attenuate melanoma growth and they develop their potential by targeting tumor growth directly, and indirectly via their interference with angiogenesis. Based on the above results, NVP-BEZ235, which has entered phase I/II clinical trials in patients with advanced solid tumors, has a potential in metastatic melanoma therapy. (Mol Cancer Res 2009;7(4):601-13)