Class IA PI3K isoforms have divergent, nonredundant cell biological roles. In untransformed cells and tissues, p110α and p110β are ubiquitously expressed, whereas p110δ expression is highly enriched in leukocytes. High levels of p110δ expression have been documented in some solid tumor cell lines, but the functional role is unknown. This study aimed to elucidate the link between elevated expression of p110δ PI3K and cancer. We report that in breast and prostate cancer cells that contain leukocyte levels of p110δ, p110δ activity dampens the activity of the PTEN tumor suppressor. Indeed, inactivation of p110δ in these cells led to PTEN activation, suppression of Akt phosphorylation, and inhibition of cell proliferation, with inhibition of PTEN activity being able to counterbalance p110δ inactivation. Likewise, forced overexpression of p110δ in cells with low p110δ expression reduced PTEN activity, resulting in increased Akt phosphorylation. Our data indicate that the oncogenic potential of p110δ PI3K overexpression might at least partially act through PTEN inactivation, and that p110δ-selective PI3K inhibitors can have a dual antitumor mechanism, namely by directly inhibiting p110δ signaling and by a broader inhibition of class I PI3K activity through PTEN activation. These data may have important implications in the intervention of breast cancer.

Class IA PI3Ks consists of three isoforms of the p110 catalytic subunit designated p110α, p110β, and p110δ which are encoded by three separate genes. Gain-of-function mutations on PIK3CA gene encoding for p110α isoform have been detected in a wide variety of human cancers whereas no somatic mutations of genes encoding for p110β or p110δ have been reported. Unlike p110α and p110β which are ubiquitously expressed, p110δ is highly enriched in leukocytes and thus the p110δ PI3K pathway has attracted more attention for its involvement in immune disorders. However, findings have been accumulated showing that the p110δ PI3K plays a seminal role in the development and progression of some hematologic malignancies. A wealth of knowledge has come from studies showing the central role of p110δ PI3K in B-cell functions and B-cell malignancies. Further data have documented that wild-type p110δ becomes oncogenic when overexpressed in cell culture models and that p110δ is the predominant isoform expressed in some human solid tumor cells playing a prominent role in these cells. Genetic inactivation of p110δ in mice models and highly-selective inhibitors of p110δ have demonstrated an important role of this isoform in differentiation, growth, survival, motility, and morphology with the inositol phosphatase PTEN to play a critical role in p110δ signaling. In this review, we summarize our understanding of the p110δ PI3K signaling pathway in hematopoietic cells and malignancies, we highlight the evidence showing the oncogenic potential of p110δ in cells of non-hematopoietic origin and we discuss perspectives for potential novel roles of p110δ PI3K in cancer.

Patient selection for PI3K-targeted solid cancer treatment was based on the PIK3CA/PTEN mutational status. However, it is increasingly clear that this is not a good predictor of the response of breast cancer cells to the anti-proliferative effect of PI3K inhibitors, indicating that isoform(s) other than p110α may modulate cancer cells sensitivity to PI3K inhibition. Surprisingly, we found that although no mutations in the p110δ subunit have been detected thus far in breast cancer, the expression of p110δ becomes gradually elevated during human breast cancer progression from grade I to grade III. Moreover, pharmacological inactivation of p110δ in mice abrogated the formation of tumours and the recruitment of macrophages to tumour sites and strongly affected the survival, proliferation and apoptosis of grafted tumour cells. Pharmacological inactivation of p110δ in mice with defective macrophages or in mice with normal macrophages but grafted with p110δ-lacking tumours suppressed only partly tumour growth, indicating a requisite role of p110δ in both macrophages and cancer cells in tumour progression. Adoptive transfer of δD910A/D910A macrophages into mice with defected macrophages suppressed tumour growth, eliminated the recruitment of macrophages to tumour sites and prevented metastasis compared with mice that received WT macrophages further establishing that inactivation of p110δ in macrophage prevents tumour progression. Our work provides the first in vivo evidence for a critical role of p110δ in cancer cells and macrophages during solid tumour growth and may pave the way for the use of p110δ inhibitors in breast cancer treatment.

The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) tumor suppressor protein is regulated by various mechanisms that are not fully understood. This includes regulation by Tyr phosphorylation by a mechanism that remains elusive. Here, we show that focal adhesion kinase (FAK) phosphorylates PTEN in vitro, in cell-free systems and in cells. Furthermore, by mass spectrometry, we identified Tyr336 on PTEN as being phosphorylated by FAK. Tyr336 phosphorylation increased phosphatase activity, protein-lipid interaction, and protein stability of PTEN. In cells, including primary mouse macrophages and human cancer cell lines, FAK was found to be negatively regulated by p110d phosphoinositide-3 kinase (PI3K), whereas the activation of FAK was positively regulated by RhoA-associated kinase (ROCK). Indeed, the phosphorylation of FAK was unexpectedly increased in macrophages derived from mice expressing kinase-dead p110d. Pharmacologic inactivation of RhoA/ROCK reduced the phosphorylation of FAK to normal levels in cells with genetically inactivated p110d. Likewise, pharmacologic inactivation of FAK reduced the phosphorylation of PTEN in cells expressing kinase-dead p110d and restored the functional defects of p110d inactivation, including Akt phosphorylation and cell proliferation. This work identifies FAK as a target of p110d PI3K that links RhoA with PTEN and establishes for the first time that PTEN is a substrate of FAK-mediated Tyr phosphorylation.-Tzenaki, N., Aivaliotis, M., Papakonstanti, E. A. Focal adhesion kinase phosphorylates the phosphatase and tensin homolog deleted on chromosome 10 under the control of p110d phosphoinositide-3 kinase. FASEB J. 29, 4840-4852 (2015). www.fasebj.org

Colony stimulating factor-1 (CSF-1) and its receptor (CSF-1R) are key regulators of macrophage biology, and their elevated expression in cancer cells has been linked to poor prognosis. CSF-1Rs are thought to function at the plasma membrane. We show here that functional CSF-1Rs are present at the nuclear envelope of various cell types, including primary macrophages, human cancer cell lines, and primary human carcinomas. In response to CSF-1, added to intact cells or isolated nuclei, nucleus-associated CSF-1R became phosphorylated and triggered the phosphorylation of Akt and p27 inside the nucleus. Extracellularly added CSF-1 was also found to colocalize with nucleus-associated CSF-1Rs. All these activities were found to depend selectively on the activity of the p110δ isoform of phosphoinositide 3-kinase (PI3K). This finding was related to the p110δ-dependent translocation of exogenous CSF-1 to the nucleus-associated CSF-1Rs, correlating with a prominent role of p110δ in activation of the Rab5 GTPase, a key regulator of the endocytic trafficking. siRNA-silencing of Rab5a phenocopied p110δ inactivation and nuclear CSF-1 signaling. Our work demonstrates for the first time the presence of functional nucleus-associated CSF-1Rs, which are activated by extracellular CSF-1 by a mechanism that involves p110δ and Rab5 activity. These findings may have important implications in cancer development.

Background Tissue factor (TF) plays an important role on blood clotting and the risk of thromboembolic events is increased in ulcerative colitis (UC). Tofacitinib, recently introduced in UC therapeutics, may further increase the risk. To delineate thrombosis pathophysiology in this context, TF expression in primary human colonic mesenchymal cells (PHCMC) of patients with active UC was correlated with clinical parameters, serum markers of inflammation and endoscopy. We then treated those PHCMC with tofacitinib with or without cytokines to better mimic the in vivo milieu they are exposed to. Methods PHCMC from endoscopic biopsies of the inflamed mucosa of 10 UC patients with an endoscopic Mayo score ≥2 were treated with all major T helper (Th)1 (TNF-α, IFN-γ), Th2 (IL-4, IL-13) or T regulatory (Treg; TGF-β, IL-10) cytokines with or without tofacitinib. Cells were lysed, RNA was isolated and reverse-transcribed to cDNA. TF and RPL4 (housekeeping) cDNAs were quantified with real-time PCR. Wilcoxon and Mann-Whitney U tests were used to compare TF ΔΔCT for paired or unpaired values, respectively, and Spearman’s rho to correlate TF ΔΔCT with scale clinical variables and continuous laboratory values. Results Increased TF mRNA abundance in PHCMC was correlated to increased partial Mayo score (Spearman's rho 0.661, p < 0.044), reduced serum albumin (Spearman's rho -0.723, p < 0.05) and to more severe endoscopic lesions: cells originating from UC patients of an endoscopic Mayo score 3 expressed 20 times more TF than those from an endoscopic Mayo score 2 (p < 0.017; Figure 1). Moreover, PHCMC from difficult-to-treat patients, defined as requiring >1 biologics, expressed 9 times more TF (Figure 2). On the other hand, treatment with tofacitinib did not upregulate TF (Figure 3). PHCMC expressed receptors and responded to treatment with all major Th1 (TNF-α, IFN-γ), Th2 (IL-4, IL-13) or Treg (TGF-β, IL-10) cytokines by further upregulating TF by 5.5-7.5 times (p 0.001-0.035). IL-13 had the maximal effect (Figure 4). Even when tofacitinib was added together with the aforementioned cytokines, it did not further upregulate TF; instead, it tended to partially inhibit their effects. For example, it decreased upregulation of TF by IL-13 by 40%. Conclusion The expression of TF mRNA in active UC is significantly associated with clinically and endoscopically severe disease and resistance to treatment. Tofacitinib per se does not increase TF. Instead, it may limit the upregulating effect of pro-inflammatory cytokines.