Interferon-γ: teammate or opponent in the tumour microenvironment?

Cancer immunotherapy offers substantive benefit to patients with various tumour types, in some cases leading to complete tumour clearance. However, many patients do not respond to immunotherapy, galvanizing the field to define the mechanisms of pre-existing and acquired resistance. Interferon-γ (IFNγ) is a cytokine that has both protumour and antitumour activities, suggesting that it may serve as a nexus for responsiveness to immunotherapy. Many cancer immunotherapies and chemotherapies induce IFNγ production by various cell types, including activated T cells and natural killer cells. Patients resistant to these therapies commonly have molecular aberrations in the IFNγ signalling pathway or express resistance molecules driven by IFNγ. Given that all nucleated cells can respond to IFNγ, the functional consequences of IFNγ production need to be carefully dissected on a cell-by-cell basis. Here, we review the cells that produce IFNγ and the different effects of IFNγ in the tumour microenvironment, highlighting the pleiotropic nature of this multifunctional and abundant cytokine.

Regulatory T Cells: Barriers of Immune Infiltration Into the Tumor Microenvironment

Regulatory T cells (T_regs) are key immunosuppressive cells that promote tumor growth by hindering the effector immune response. T_regs utilize multiple suppressive mechanisms to inhibit pro-inflammatory responses within the tumor microenvironment (TME) by inhibition of effector function and immune cell migration, secretion of inhibitory cytokines, metabolic disruption and promotion of metastasis. In turn, T_regs are being targeted in the clinic either alone or in combination with other immunotherapies, in efforts to overcome the immunosuppressive TME and increase anti-tumor effects. However, it is now appreciated that T_regs not only suppress cells intratumorally via direct engagement, but also serve as key interactors in the peritumor, stroma, vasculature and lymphatics to limit anti-tumor immune responses prior to tumor infiltration. We will review the suppressive mechanisms that T_regs utilize to alter immune and non-immune cells outside and within the TME and discuss how these mechanisms collectively allow T_regs to create and promote a physical and biological barrier, resulting in an immune-excluded or limited tumor microenvironment.

Abstract 1430: CaMKK2 regulates EGF-dependent activation of oncogenic Akt in ovarian cancer cells

Background-The canonical PI3K/Akt pathway is hyperactive in a variety of cancers including ovarian cancer (OVCa). Using baculovirus-expressed, FPLC-purified enzymes, we previously demonstrated that Calcium/Calmodulin-dependent CaM Kinase Kinase 2 (CaMKK2) activates the oncogene Akt by direct phosphorylation of its primary activation site T308. In OVCAR-3 and other OVCa cells, RNAi-mediated knockdown of CaMKK2 decreased basal Akt phosphorylation at T308 in a Phosphoinositide-Dependent Kinase-1 (PDK1)-independent manner. CaMKK2 knockdown also decreased Akt phosphorylation at its secondary activation site, S473 by an apparently indirect mechanism.

Results- In this study we show that CaMKK2 mediates downstream effects of epidermal growth factor (EGF) on the Akt cascade in OVCa cells. Treatment of OVCAR3 cells with EGF produced a prominent enhancement of p-Akt T308 which was reduced ~2-fold, by either CaMKK2 or PDK1 knockdowns. Knockdown of CaMKK2 but not PDK1 reduced p-Akt S473 after EGF treatment. Similar results were obtained with Insulin-like growth factor 1 (IGF1). To discern how CaMKK2 is engaged by EGF action we examined whether, in vitro, CaMKK2 phosphorylation of WT Akt or a synthetic peptide encompassing T308 is stimulated by Calcium/CaM and/or Phosphatidylinositol (3,4,5)-trisphosphate (PIP3). CaMKK2 activity was enhanced by Calcium/CaM but not by soluble PIP3. CaMKK2 did not bind to a dot blot of various phosphoinositides, although strong binding to PIP3 was observed with PDK1. Alternatively, Akt regulation by CaMKK2 may occur via a Calcium/CaM-dependent pathway. Increased p-Akt T308 and S473 upon treatment of cells with the calcium-ionophore, ionomycin, was significantly reduced by CaMKK2 knockdown. EGF stimulation of Akt phosphorylation at both T308 and S473 was significantly reduced by the intracellular calcium chelator, BAPTA-AM and by the CaM inhibitor, W7. We also probed the mechanism by which optimal cellular Akt phosphorylation at S473 requires CaMKK2. mTOR complex 2 (mTORC2) and DNA-dependent protein kinase (DNA-PKcs) are considered candidate kinases for p-Akt S473. CaMKK2 knockdown regulated p-Akt S473 in M059J cells, a DNA-PKcs null cell line similarly to that observed with OVCAR3 cells, suggesting that mTORC2 may be regulated by CaMKK2. Using an MS/MS Protein-protein interaction (PPI) screen we observed CaMMK2 interaction with multiple ribosomal proteins an observation consistent with suggested mTORC2 ribosomal regulation of Akt S473 phosphorylation.

Conclusions-This study documents Akt activating phosphorylation by CaMKK2 in response to EGF in a Calcium/CaM-dependent, PI3K/PIP3 independent, manner. Besides directly phosphorylating Akt at T308, CaMKK2 regulates p-Akt S473 potentially through the regulation of mTORC2 activity. Our results highlight the importance of CaMKK2 activated by growth factor signals as a parallel system to the oncogenic PI3K/PDK1 pathway.

Citation Format: Shuhang Dai, Angela M. Gocher, Arthur M. Edelman. CaMKK2 regulates EGF-dependent activation of oncogenic Akt in ovarian cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1430.

Neuropilin-1 is a T cell memory checkpoint limiting long-term antitumor immunity

Robust CD8⁺ T cell memory is essential for long-term protective immunity, but is often compromised in cancer where T cell exhaustion leads to loss of memory precursors. Immunotherapy via checkpoint blockade may not effectively reverse this defect, potentially underlying disease relapse. Here we report that mice with a CD8⁺ T cell-restricted neuropilin-1 (NRP1) deletion exhibited substantially enhanced protection from tumor re-challenge and sensitivity to anti-PD1 immunotherapy, despite unchanged primary tumor growth. Mechanistically, NRP1 cell-intrinsically limited the self-renewal of the CD44⁺PD1⁺TCF1⁺TIM3^– progenitor exhausted T cells (pT_EX), which was associated with their reduced ability to induce c-Jun/AP-1 expression upon T cell receptor (TCR) re-stimulation, a mechanism that may contribute to terminal T cell exhaustion at the cost of memory differentiation in wildtype tumor-bearing hosts. These data suggest that blockade of NRP1, a unique “immune memory checkpoint”, may promote the development of long-lived tumor-specific T_MEM that are essential for durable anti-tumor immunity.

Akt activation by Ca2+/calmodulin-dependent protein kinase kinase 2 (CaMKK2) in ovarian cancer cells

Hyperactivation of Akt is associated with oncogenic changes in the growth, survival, and chemoresistance of cancer cells. The PI3K/phosphoinositide-dependent kinase (PDK) 1 pathway represents the canonical mechanism for phosphorylation of Akt at its primary activation site, Thr-308. We observed that Ca²⁺/calmodulin (CaM)-dependent protein kinase kinase 2 (β) (CaMKK2) is highly expressed in high-grade serous ovarian cancer, and we investigated its role in Akt activation in ovarian cancer (OVCa) cell lines (OVCAR-3, SKOV-3, and Caov-3). Knockdown or pharmacological inhibition of CaMKK2 produced phenotypes expected of Akt inhibition, including reductions in cell growth and cell viability and in the regulation of Akt downstream targets involved in G₁/S transition and apoptosis. CaMKK2 knockdown or inhibition decreased Akt phosphorylation at Thr-308 and Ser-473 to extents similar to those of PDK1 knockdown or PI3K inhibition. Combined CaMKK2 and PDK1 knockdown or CaMKK and PI3K inhibition, respectively, produced additive effects on p-Akt and cell growth, consistent with direct Akt phosphorylation by CaMKK2. This conclusion was supported by the absence of effects of CaMKK2 knockdown/inhibition on alternative means of activating Akt via p-Akt Thr-450, p-PDK1 Ser-241, or p-IRS1 Ser-636/639. Recombinant CaMKK2 directly activated recombinant Akt by phosphorylation at Thr-308 in a Ca²⁺/CaM-dependent manner. In OVCa cells, p-Akt Thr-308 was significantly inhibited by intracellular Ca²⁺_i chelation or CaM inhibition. Ionomycin-induced Ca²⁺ influx promoted p-Akt, an effect blocked by PDK1, and/or CaMKK2, siRNAs, and by PI3K and/or CaMKK inhibitors. CaMKK2 knockdown potentiated the effects of the chemotherapeutic drugs carboplatin and PX-866 to reduce proliferation and survival of OVCa cells.

Nucleoporin 62 and Ca(2+)/calmodulin dependent kinase kinase 2 regulate androgen receptor activity in castrate resistant prostate cancer cells

BACKGROUND

Re-activation of the transcriptional activity of the androgen receptor (AR) is an important factor mediating progression from androgen-responsive to castrate-resistant prostate cancer (CRPC). However, the mechanisms regulating AR activity in CRPC remain incompletely understood. Ca(2+) /calmodulin-dependent kinase kinase (CaMKK) 2 was previously shown to regulate AR activity in androgen-responsive prostate cancer cells. Our objective was to further explore the basis of this regulation in CRPC cells.

METHODS

The abundance of CaMKK2 in nuclear fractions of androgen-responsive prostate cancer and CRPC, cells were determined by subcellular fractionation and Western blotting. CaMKK2 association with nuclear pore complexes (NPCs) and nucleoporins (Nups) including Nup62, were imaged by structured illumination and super-resolution fluorescence microscopy and co-immunoprecipitation, respectively. The abundance and subcellular localization of CaMKK2 and Nup62 in human clinical specimens of prostate cancer was visualized by immunohistochemistry. The role of Nups in the growth and viability of CRPC cells was assessed by RNA interference and cell counting. The involvement of CaMKK2 and Nup62 in regulating AR transcriptional activity was addressed by RNA interference, chromatin immunoprecipitation, androgen response element reporter assay, and Western blotting.

RESULTS

CaMKK2 was expressed at higher levels in the nuclear fraction of CPRC C4-2 cells, than in that of androgen-responsive LNCaP cells. In C4-2 cells, CaMKK2 associated with NPCs of the nuclear envelope and physically interacted with Nup62. CaMKK2 and Nup62 demonstrated pronounced, and similar increases in both expression and perinuclear/nuclear localization in human clinical specimens of advanced prostate cancer relative to normal prostate. Knockdown of Nup62, but not of Nups, 98 or 88, reduced growth and viability of C4-2 cells. Knockdown of Nup62 produced a greater reduction of the growth and viability of C4-2 cells than of non-neoplastic RWPE-1 prostatic cells. Nup62, CaMKK2, and the AR were recruited to androgen response elements of the AR target genes, prostate specific antigen, and transmembrane protease, serine 2. Knockdown of CaMKK2 and Nup62 reduced prostate specific antigen expression and AR transcriptional activity driven by androgen response elements from the prostate-specific probasin gene promoter.

CONCLUSION

Nup62 and CaMKK2 are required for optimal AR transcriptional activity and a potential mechanism for AR re-activation in CRPC.

Abstract B13: Regulation of Akt activity, cell proliferation, and viability in ovarian cancer cells by calcium/calmodulin-dependent protein kinase kinase 2

Calcium/Calmodulin-dependent protein kinase kinase 2 (CaMKK2) has been implicated in the regulation of G1/S phase cell cycle progression in prostate and breast cancer but has not been studied in ovarian cancer (OvCa). We report here the following. CaMKK2 is abundantly expressed in high grade serous papillary cystadenocarcinoma. Knockdown (KD) of CaMKK2 expression using RNAi in OVCAR-3 OvCa cells resulted in slowing of cell growth, decreased cyclin D1 protein and mRNA, decreased phosphorylation of the tumor suppressor protein Rb at Ser807/811 and decreased DNA synthesis, indicating an arrest at the G1/S interface. CaMKK2 KD decreased cell viability, increased PARP cleavage and increased Caspase-3/7 activity suggesting apoptosis induction by CaMKK2 loss. CaMKK2 KD decreased p-Akt at Thr308 to a similar extent (59.3%) as that of PDK1 KD (50.4%) in OVCAR-3 cells. Combined CaMKK2 and PDK1 KDs led to an additive (80.7%) decrease in p-Akt suggesting that CaMKK2 regulates Akt activating phosphorylation independently of the canonical-PDK1 pathway. Additive effects of combined PDK1/CaMKK2 KD on p-Akt Thr308 in SKOV-3 OvCa cells were also obtained. The ability of baculovirus expressed and purified Akt to phosphorylate a specific peptide substrate was enhanced at least 9-fold by purified CaMKK2, whereas kinase activity of Akt T308A/S473A was not increased by CaMKK2. Direct phosphorylation of baculovirus expressed Akt at Thr308 by CaMKK2 was confirmed by Western blotting using Akt phospho-specific antibodies. Altogether these data show that CaMKK2 regulates cell growth and viability in OvCa cells and directly phosphorylates Akt to promote its activity via a non-PDK1-dependent pathway. These data indicate that CaMKK2 may be a novel therapeutic target for OvCa in combination with a PI3K inhibitor.

Citation Format: Angela M. Gocher, Thomas F. Franke, Gissou Azabdaftari, Loukia G. Karacosta, Arthur M. Edelman. Regulation of Akt activity, cell proliferation, and viability in ovarian cancer cells by calcium/calmodulin-dependent protein kinase kinase 2. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr B13.

Abstract A12: Regulation of ovarian cancer OVCAR-3 cell proliferation and viability by calcium/calmodulin-dependent protein kinase kinase 2

Protein kinases play crucial roles in cancer progression and are considered potential targets for novel anti-cancer therapeutics. Oncogenic kinases mediate a variety of events characteristic of the malignant phenotype including transcriptional activation, accelerated cell proliferation and enhanced cellular survival. Ca2+/Calmodulin-dependent Protein Kinase Kinase 2 (CaMKK2) has been implicated as a signaling mechanism in prostate and breast cancers, but has not been studied in ovarian cancer (OvCa). We report here the following. CaMKK2 expression is greatly increased in high grade serous papillary cystadenocarcinoma compared to benign tissue. Knockdown of CaMKK2 expression by RNA interference in OvCa OVCAR-3 cells resulted in slowing of cell growth and decreased number of cells entering S phase. At the molecular level, CaMKK2 knockdown led to significant decreases in cyclin D1 expression at both mRNA and protein levels and to a drop in phosphorylation of the retinoblastoma tumor suppressor (Rb) at Ser 807/811. These results indicate that CaMKK2 expression in OVCAR-3 OvCa cells is required for optimal G1/S phase cell cycle progression and proliferation. CaMKK2 knockdown also resulted in a significant decrease in OVCAR-3 cell survival and an increase in both Poly ADP Ribose Polymerase (PARP) cleavage (inactivation) and in the activity of executioner Caspases-3/7 indicating that CaMKK2 knockdown in OVCAR-3 cells results in apoptosis. Preliminary data showed a decrease in phosphorylation of the activation site of Akt (Thr 308) in CaMKK2 depleted cells suggesting that the G1/S phase cell cycle arrest and apoptosis in CaMKK2 silenced cells may occur either directly or indirectly through an Akt-dependent pathway. Altogether these data show that CaMKK2 is required for optimal growth and viability of OVCAR-3 cells and furthermore imply that CaMKK2 may be a promising and novel therapeutic target for OvCa.

Citation Format: Angela M. Gocher, Gissou Azabdaftari, Arthur M. Edelman. Regulation of ovarian cancer OVCAR-3 cell proliferation and viability by calcium/calmodulin-dependent protein kinase kinase 2. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr A12.