Metabolic vulnerability of cancer stem cells and their niche.

Cancer stem cells (CSC) are the leading cause of the failure of anti-tumor treatments. These aggressive cancer cells are preserved and sustained by adjacent cells forming a specialized microenvironment, termed niche, among which tumor-associated macrophages (TAMs) are critical players. The cycle of tricarboxylic acids, fatty acid oxidation path, and electron transport chain have been proven to play central roles in the development and maintenance of CSCs and TAMs. By improving their oxidative metabolism, cancer cells are able to extract more energy from nutrients, which allows them to survive in nutritionally defective environments. Because mitochondria are crucial bioenergetic hubs and sites of these metabolic pathways, major hopes are posed for drugs targeting mitochondria. A wide range of medications targeting mitochondria, electron transport chain complexes, or oxidative enzymes are currently investigated in phase 1 and phase 2 clinical trials against hard-to-treat tumors. This review article aims to highlight recent literature on the metabolic adaptations of CSCs and their supporting macrophages. A focus is provided on the resistance and dormancy behaviors that give CSCs a selection advantage and quiescence capacity in particularly hostile microenvironments and the role of TAMs in supporting these attitudes. The article also describes medicaments that have demonstrated a robust ability to disrupt core oxidative metabolism in preclinical cancer studies and are currently being tested in clinical trials.

The FKBP51s Splice Isoform Predicts Unfavorable Prognosis in Patients with Glioblastoma.

The primary treatment for glioblastoma (GBM) is removing the tumor mass as defined by MRI. However, MRI has limited diagnostic and predictive value. Tumor-associated macrophages (TAM) are abundant in GBM tumor microenvironment (TME) and are found in peripheral blood (PB). FKBP51 expression, with its canonical and spliced isoforms, is constitutive in immune cells and aberrant in GBM. Spliced FKBP51s supports M2 polarization. To find an immunologic signature that combined with MRI could advance in diagnosis, we immunophenotyped the macrophages of TME and PB from 37 patients with GBM using FKBP51s and classical M1-M2 markers. We also determined the tumor levels of FKBP51s, PD-L1, and HLA-DR. Tumors expressing FKBP51s showed an increase in various M2 phenotypes and regulatory T cells in PB, indicating immunosuppression. Tumors expressing FKBP51s also activated STAT3 and were associated with reduced survival. Correlative studies with MRI and tumor/macrophages cocultures allowed to interpret TAMs. Tumor volume correlated with M1 infiltration of TME. Cocultures with spheroids produced M1 polarization, suggesting that M1 macrophages may infiltrate alongside cancer stem cells. Cocultures of adherent cells developed the M2 phenotype CD163/FKBP51s expressing pSTAT6, a transcription factor enabling migration and invasion. In patients with recurrences, increased counts of CD163/FKBP51s monocyte/macrophages in PB correlated with callosal infiltration and were accompanied by a concomitant decrease in TME-infiltrating M1 macrophages. PB PD-L1/FKBP51s connoted necrotic tumors. In conclusion, FKBP51s identifies a GBM subtype that significantly impairs the immune system. Moreover, FKBP51s marks PB macrophages associated with MRI features of glioma malignancy that can aid in patient monitoring. SIGNIFICANCE: Our research suggests that by combining imaging with analysis of monocyte/macrophage subsets in patients with GBM, we can enhance our understanding of the disease and assist in its treatment. We discovered a similarity in the macrophage composition between the TME and PB, and through association with imaging, we could interpret macrophages. In addition, we identified a predictive biomarker that drew more attention to immune suppression of patients with GBM.

Scaffold proteins of cancer signaling networks: The paradigm of FK506 binding protein 51 (FKBP51) supporting tumor intrinsic properties and immune escape.

Scaffold proteins are crucial regulators of signaling networks, and their abnormal expression may favor the development of tumors. Among the scaffold proteins, immunophilin covers a unique role as 'protein-philin' (Greek 'philin' = friend) that interacts with proteins to guide their proper assembly. The growing list of human syndromes associated with the immunophilin defect underscores the biological relevance of these proteins that are largely opportunistically exploited by cancer cells to support and enable the tumor's intrinsic properties. Among the members of the immunophilin family, the FKBP5 gene was the only one identified to have a splicing variant. Cancer cells impose unique demands on the splicing machinery, thus acquiring a particular susceptibility to splicing inhibitors. This review article aims to overview the current knowledge of the FKBP5 gene functions in human cancer, illustrating how cancer cells exploit the scaffolding function of canonical FKBP51 to foster signaling networks that support their intrinsic tumor properties and the spliced FKBP51s to gain the capacity to evade the immune system.

FKBP51 plays an essential role in Akt ubiquitination that requires Hsp90 and PHLPP.

FKBP51 plays a relevant role in sustaining cancer cells, particularly melanoma. This cochaperone participates in several signaling pathways. FKBP51 forms a complex with Akt and PHLPP, which is reported to dephosphorylate Akt. Given the recent discovery of a spliced FKBP51 isoform, in this paper, we interrogate the canonical and spliced isoforms in regulation of Akt activation. We show that the TPR domain of FKBP51 mediates Akt ubiquitination at K63, which is an essential step for Akt activation. The spliced FKBP51, lacking such domain, cannot link K63-Ub residues to Akt. Unexpectedly, PHLPP silencing does not foster phosphorylation of Akt, and its overexpression even induces phosphorylation of Akt. PHLPP stabilizes levels of E3-ubiquitin ligase TRAF6 and supports K63-ubiquitination of Akt. The interactome profile of FKBP51 from melanoma cells highlights a relevant role for PHLPP in improving oncogenic hallmarks, particularly, cell proliferation.

Alternative splicing of FKBP5 gene exerts control over T lymphocyte expansion.

FKBP51 is constitutively expressed by immune cells. As other FKBP family members, FKBP51 acts as a coreceptor for the natural products FK506 and rapamycin, which exhibit immunosuppressive effects. However, little is known about the intrinsic role of this large FKBP in the primary function of lymphocytes, that is, the adaptive immune response against foreign antigens, for example, pathogens. This paper aimed to investigate whether FKBP51 expression was modulated during lymphocyte activation. Moreover, as we recently identified a splicing isoform of FKBP51, namely FKBP51s, we also measured this splice protein, along with the canonical one, at different times of a peripheral blood mononuclear cell culture stimulated via T cell receptor. Our results show that the two FKBP51 isoforms were alternatively induced during the proliferative burst. Canonical FKBP51 increased in the time window between 48 and 96 h and its expression levels correlated with cyclin D levels. FKBP51s transiently increased earlier, at 24-36 h to reappearing later, at 120 h, when cyclin D expression returned at resting levels and proliferation ceased. Interestingly, within these two specific timeframes, FKBP51s accumulated in the nucleus. Here FKBP51s colocalized with the Foxp3 transcription factor at 36 h. Regulatory T cell (Treg) counts significantly decreased when FKBP51s was downmodulated. The coculture suppression assay suggested that FKBP51s supports the suppressive capability of Tregs. At 120 h, chromatin immunoprecipitation experiments found FKBP51s linked to CCND1 gene, suggesting a possible effect on gene transcription regulation, as previously demonstrated in melanoma. In conclusion, our study shows that FKBP5 isoforms are upregulated during lymphocyte activation, albeit on different timeframes. The activation of canonical FKBP51 coincides with proliferation hallmarks; FKBP5 splicing occurs early to sustain Treg development and late when proliferation ceases.

Biological relevance of ZNF224 expression in chronic lymphocytic leukemia and its implication IN NF-kB pathway regulation.

Chronic lymphocytic leukemia (CLL) is a heterogeneous disease, whose presentation and clinical course are highly variable. Identification of novel prognostic factors may contribute to improving the CLL classification and providing indications for treatment options. The zinc finger protein ZNF224 plays a key role in cell transformation, through the control of apoptotic and survival pathways. In this study, we evaluated the potential application of ZNF224 as a novel marker of CLL progression and therapy responsiveness. To this aim, we analyzed ZNF224 expression levels in B lymphocytes from CLL patients at different stages of the disease and in patients showing different treatment outcomes. The expression of ZNF224 was significantly increased in disease progression and dramatically decreased in patients in complete remission after chemotherapy. Gene expression correlation analysis performed on datasets of CLL patients revealed that ZNF224 expression was well correlated with that of some prognostic and predictive markers. Moreover, bioinformatic analysis coupled ZNF224 to NF-κB pathway, and experimental data demonstrated that RNA interference of ZNF224 reduced the activity of the NF-κB survival pathway in CLL cells. Consistently with a pro-survival role, ZNF224 knockdown raised spontaneous and drug-induced apoptosis and inhibited the proliferation of peripheral blood mononuclear cells from CLL patients. Our findings provide evidence for the involvement of ZNF224 in the survival of CLL cells via NF-κB pathway modulation, and also suggest ZNF224 as a prognostic and predictive molecular marker of CLL disease.

FKBP51 Affects TNF-Related Apoptosis Inducing Ligand Response in Melanoma.

Melanoma is one of the most immunogenic tumors and has the highest potential to elicit specific adaptive antitumor immune responses. Immune cells induce apoptosis of cancer cells either by soluble factors or by triggering cell-death pathways. Melanoma cells exploit multiple mechanisms to escape immune system tumoricidal control. FKBP51 is a relevant pro-oncogenic factor of melanoma cells supporting NF-κB-mediated resistance and cancer stemness/invasion epigenetic programs. Herein, we show that FKBP51-silencing increases TNF-related apoptosis-inducing ligand (TRAIL)-R2 (DR5) expression and sensitizes melanoma cells to TRAIL-induced apoptosis. Consistent with the general increase in histone deacetylases, as by the proteomic profile, the immune precipitation assay showed decreased acetyl-Yin Yang 1 (YY1) after FKBP51 depletion, suggesting an impaired repressor activity of this transcription factor. ChIP assay supported this hypothesis. Compared with non-silenced cells, a reduced acetyl-YY1 was found on the DR5 promoter, resulting in increased DR5 transcript levels. Using Crispr/Cas9 knockout (KO) melanoma cells, we confirmed the negative regulation of DR5 by FKBP51. We also show that KO cells displayed reduced levels of acetyl-EP300 responsible for YY1 acetylation, along with reduced acetyl-YY1. Reconstituting FKBP51 levels contrasted the effects of KO on DR5, acetyl-YY1, and acetyl-EP300 levels. In conclusion, our finding shows that FKBP51 reduces DR5 expression at the transcriptional level by promoting YY1 repressor activity. Our study supports the conclusion that targeting FKBP51 increases the expression level of DR5 and sensitivity to TRAIL-induced cell death, which can improve the tumoricidal action of immune cells.

PD-L1 Expression Fluctuates Concurrently with Cyclin D in Glioblastoma Cells.

Despite Glioblastoma (GBM) frequently expressing programmed cell death ligand-1 (PD-L1), treatment with anti-programmed cell death-1 (PD1) has not yielded brilliant results. Intratumor variability of PD-L1 can impact determination accuracy. A previous study on mouse embryonic fibroblasts (MEFs) reported a role for cyclin-D in control of PD-L1 expression. Because tumor-cell growth within a cancer is highly heterogeneous, we looked at whether PD-L1 and its cochaperone FKBP51s were influenced by cell proliferation, using U251 and SF767 GBM-cell-lines. PD-L1 was measured by Western blot, flow cytometry, confocal-microscopy, quantitative PCR (qPCR), CCND1 by qPCR, FKBP51s by Western blot and confocal-microscopy. Chromatin-Immunoprecipitation assay (xChIp) served to assess the DNA-binding of FKBP51 isoforms. In the course of cell culture, PD-L1 appeared to increase concomitantly to cyclin-D on G1/S transition, to decrease during exponential cell growth progressively. We calculated a correlation between CCND1 and PD-L1 gene expression levels. In the temporal window of PD-L1 and CCND1 peak, FKBP51s localized in ER. When cyclin-D declined, FKBP51s went nuclear. XChIp showed that FKBP51s binds CCND1 gene in a closed-chromatin configuration. Our finding suggests that the dynamism of PD-L1 expression in GBM follows cyclin-D fluctuation and raises the hypothesis that FKBP51s might participate in the events that govern cyclin-D oscillation.

Combining Magnetic Resonance Imaging with Systemic Monocyte Evaluation for the Implementation of GBM Management.

Magnetic resonance imaging (MRI) is the gold standard for glioblastoma (GBM) patient evaluation. Additional non-invasive diagnostic modalities are needed. GBM is heavily infiltrated with tumor-associated macrophages (TAMs) that can be found in peripheral blood. FKBP51s supports alternative-macrophage polarization. Herein, we assessed FKBP51s expression in circulating monocytes from 14 GBM patients. The M2 monocyte phenotype was investigated by qPCR and flow cytometry using antibodies against PD-L1, CD163, FKBP51s, and CD14. MRI assessed morphologic features of the tumors that were aligned to flow cytometry data. PD-L1 expression on circulating monocytes correlated with MRI tumor necrosis score. A wider expansion in circulating CD163/monocytes was measured. These monocytes resulted in a dramatic decrease in patients with an MRI diagnosis of complete but not partial surgical removal of the tumor. Importantly, in patients with residual tumor, most of the peripheral monocytes that in the preoperative stage were CD163/FKBP51s- had turned into CD163/FKBP51s+. After Stupp therapy, CD163/FKBP51s+ monocytes were almost absent in a case of pseudoprogression, while two patients with stable or true disease progression showed sustained levels in such circulating monocytes. Our work provides preliminary but meaningful and novel results that deserve to be confirmed in a larger patient cohort, in support of potential usefulness in GBM monitoring of CD163/FKBP51s/CD14 immunophenotype in adjunct to MRI.

Thrombocytopenia Complicating Transcatheter Aortic Valve Implantation: Differences Between Two New-Generation Devices.

Thrombocytopenia after TAVI is common and clinically detrimental. Retrospectively, we observed Portico recipients had a more profound platelet drop than Evolut recipients. We thus investigated periprocedural platelet damage and/orpro-inflammatory state in 64 TAVI recipients at baseline and after implantation. Platelet damage was assessed by annexin V staining and monocyte-phagocytic phenotype was assessed according to CD14/CD36 expression. Serum cytokines were measured in 20 patients. The formaldehyde-based storage solution altered platelets. When, before being loaded onto the delivery system, Portico underwent one additional flushing to those recommended, the receiving patients showed thrombocytopenia, platelet damage, and CD36-monocyte count were mitigated. A general increase in IL-6 was recorded in overall TAVI recipients, but a high serum level of IL-8, a potent thrombocytopenia inducer, was measured in Portico recipients only, including those with extra-rinsed valve. Our study suggests a platelet-injury effect by storage-solution and generates the hypothesis of a role for the biomaterial in stimulating innate-immunity. Larger prospective studies are needed. Graphical Abstract.

Alternative macrophage polarisation associated with resistance to anti-PD1 blockade is possibly supported by the splicing of FKBP51 immunophilin in melanoma patients.

BACKGROUND: FKBP51 immunophilin is abundantly expressed by immune cells. Co-inhibitory immune receptor signalling generates the splicing isoform FKBP51s. Tregs stained by FKBP51s are increased in melanoma patients and their counts are associated with anti-CTLA-4 response. An expansion of FKBP51s+PD-L1+ monocytes was measured in a group of non-responding patients to anti-CTLA-4. The aim of this work was to confirm the predictive value of response of FKBP51s+Tregs in a cohort of patients undergoing anti-PD1 treatment and shed light on a monocyte subset co-expressing PD-L1/FKBP51s. METHODS: Co-cultures of organoids and autologous lymphocytes were used to confirm that tumour T-cell interaction can induce FKBP51s. PBMC immunophenotype and flow cytometry served to assess and monitor FKBP51s+Treg and FKBP51s+PD-L1+ monocytes in 22 advanced melanoma patients treated with anti-PD1. Silencing and overexpression of FKBP51s in human macrophages served to address the protein role in the tolerant macrophages' behaviour. RESULTS: FKBP51s+Tregs count was increased in responders and had a prognostic value. Non-responders showed an early increase in FKBP51s+ PD-L1+ monocytes during anti-PD1 treatment. Manipulation of FKBP51s modulated the macrophage-phenotype, with forced protein expression promoting aspects associated with tolerance. CONCLUSIONS: FKBP51s may guide in the selection and monitoring of melanoma patient candidates to immune-checkpoint-targeted therapy. Manipulation of FKBP51s may overcome resistance.

Manipulation of the Immune System for Cancer Defeat: A Focus on the T Cell Inhibitory Checkpoint Molecules.

The immune system actively counteracts the tumorigenesis process; a breakout of the immune system function, or its ability to recognize transformed cells, can favor cancer development. Cancer becomes able to escape from immune system control by using multiple mechanisms, which are only in part known at a cellular and molecular level. Among these mechanisms, in the last decade, the role played by the so-called "inhibitory immune checkpoints" is emerging as pivotal in preventing the tumor attack by the immune system. Physiologically, the inhibitory immune checkpoints work to maintain the self-tolerance and attenuate the tissue injury caused by pathogenic infections. Cancer cell exploits such immune-inhibitory molecules to contrast the immune intervention and induce tumor tolerance. Molecular agents that target these checkpoints represent the new frontier for cancer treatment. Despite the heterogeneity and multiplicity of molecular alterations among the tumors, the immune checkpoint targeted therapy has been shown to be helpful in selected and even histologically different types of cancer, and are currently being adopted against an increasing variety of tumors. The most frequently used is the moAb-based immunotherapy that targets the Programmed Cell Death 1 protein (PD-1), the PD-1 Ligand (PD-L1) or the cytotoxic T lymphocyte antigen-4 (CTLA4). However, new therapeutic approaches are currently in development, along with the discovery of new immune checkpoints exploited by the cancer cell. This article aims to review the inhibitory checkpoints, which are known up to now, along with the mechanisms of cancer immunoediting. An outline of the immune checkpoint targeting approaches, also including combined immunotherapies and the existing trials, is also provided. Notwithstanding the great efforts devoted by researchers in the field of biomarkers of response, to date, no validated FDA-approved immunological biomarkers exist for cancer patients. We highlight relevant studies on predictive biomarkers and attempt to discuss the challenges in this field, due to the complex and largely unknown dynamic mechanisms that drive the tumor immune tolerance.

Cell stemness, epithelial-to-mesenchymal transition, and immunoevasion: Intertwined aspects in cancer metastasis.

Recent advances in tumor immunology, fostered by dramatic outcomes with cancer immunotherapy, have opened new scenarios in cancer metastasis. The cancer stemness/mesenchymal phenotype and an excess of immune suppressive signals are emerging as Intertwined aspects of human tumors. This review examines recent studies that explored the mechanistic links between cancer cell stemness and immunoevasion, and the evidence points to these key events in cancer metastasis as two sides of the same coin. This review also covers the mechanisms involved in tumor expression of programmed cell death ligand 1 (PD-L1), a major factor exploited by human neoplasias to suppress immune control. We highlight the convergence of mesenchymal traits and PD-L1 expression and examine the functions of this immune inhibitory molecule, which confers cancer cell resistance and aggressiveness.

Neural crest-derived tumor neuroblastoma and melanoma share 1p13.2 as susceptibility locus that shows a long-range interaction with the SLC16A1 gene.

Neuroblastoma (NB) and malignant cutaneous melanoma (CMM) are neural crest cells (NCC)-derived tumors and may have a shared genetic basis, but this has not been investigated systematically by genome-wide association studies (GWAS). We took a three-staged approach to conduct cross-disease meta-analysis of GWAS for NB and CMM (2101 NB cases and 4202 controls; 12 874 CMM cases and 23 203 controls) to identify shared loci. Findings were replicated in 1403 NB cases and 1403 controls of European ancestry and in 636 NB, 508 CMM cases and 2066 controls of Italian origin. We found a cross-association at locus 1p13.2 (rs2153977, odds ratio = 0.91, P = 5.36 × 10-8). We also detected a suggestive (P < 10-7) NB-CMM cross-association at 2q37.1 with opposite effect on cancer risk. Pathway analysis of 110 NB-CMM risk loci with P < 10-4 demonstrated enrichment of biological processes such as cell migration, cell cycle, metabolism and immune response, which are essential of human NCC development, underlying both tumors. In vitro and in silico analyses indicated that the rs2153977-T protective allele, located in an NB and CMM enhancer, decreased expression of SLC16A1 via long-range loop formation and altered a T-box protein binding site. Upon depletion of SLC16A1, we observed a decrease of cellular proliferation and invasion in both NB and CMM cell lines, suggesting its role as oncogene. This is the largest study to date examining pleiotropy across two NC cell-derived tumors identifying 1p13.2 as common susceptibility locus for NB and CMM risk. We demonstrate that combining genome-wide association studies results across cancers with same origins can identify new loci common to neuroblastoma and melanoma arising from tissues which originate from neural crest cells. Our results also show 1p13.2 confer risk to neuroblastoma and melanoma by regulating SLC16A1.

The splicing FK506-binding protein-51 isoform plays a role in glioblastoma resistance through programmed cell death ligand-1 expression regulation.

Gliomas aberrantly express programmed cell death ligand-1 (PD-L1), which has a pivotal role in immunoevasion. The splicing isoform of FKBP5, termed FKBP51s, is a PD-L1 foldase, assisting the immune checkpoint molecule in maturation and expression on the plasma membrane. The concept that PD-L1 supports tumor-intrinsic properties is increasingly emerging. The aim of the present work was to confirm the pro-tumoral effect of PD-L1 on human glioma cell survival, stemness capacity and resistance, and to address the issue of whether, by targeting its foldase either chemically or by silencing, the aggressive tumor features could be attenuated. PD-L1-depleted glioma cells have a reduced threshold for apoptosis, while PD-L1 forced expression increases resistance. Similar results were obtained with FKBP51s modulation. The ability of PD-L1 to counteract cell death was hampered by FKBP51s silencing. PD-L1 expression was particularly high in glioma cells with a cancer-stem-cell profile. Moreover, PD-L1 sustained the spheroid formation capability of glioma cells. Targeting of FKBP51s by small-interfering RNA (siRNA) or the specific inhibitor SAFit2, reduced the number of formed spheroids, along with PD-L1 expression. Finally, in an orthotopic mouse model of glioblastoma, daily treatment with SAFit2 significantly reduced tumor PD-L1 expression, and tumor growth. In treated mice, caspase-3 activation and reduced vimentin expression were observed in excised tumors. In conclusion, targeting of FKBP51s hampers PD-L1 and its pro-tumoral properties, thereby affecting the self-renewal and growth capacities of glioblastoma cells in vitro and in vivo.

Tirofiban Positively Regulates ß1 Integrin and Favours Endothelial Cell Growth on Polylactic Acid Biopolymer Vascular Scaffold (BVS).

An unexpectedly high incidence of thrombosis in patients that received the polylactic acid bioresorbable vascular scaffold (BVS) suggests a delayed/incomplete endothelial repair with this stent. The anti-platelet agent tirofiban stimulates endothelial cell migration and proliferation, mediated by VEGF production. We investigated the tirofiban effect on the migration and adhesion of endothelial cells to BVS, in vitro. We performed human umbilical endothelial cell (HUVEC) cultures in the presence of BVS. Tirofiban, similarly to VEGF, increased the ability of HUVEC to grow on the vascular scaffold, compared to unstimulated or abciximab-treated cells. Tirofiban increased HUVEC expression of ß1 and ß3 integrins along with collagen and fibronectin. A role for ß1 integrin in the "pro-adhesive and -migratory" signals elicited by tirofiban was suggested by use of an anti-ß1-blocking antibody that prevented poly-levo-lactic acid vascular scaffold colonization. Our study suggests that tirofiban may improve the outcomes of patients receiving BVS by accelerating stent endothelization.

A regulatory role for the co-chaperone FKBP51s in PD-L1 expression in glioma.

BACKGROUND: FKBP51 is a co-chaperone with isomerase activity, abundantly expressed in glioma. We previously identified a spliced isoform (FKBP51s) and highlighted a role for this protein in the upregulation of Programmed Death Ligand 1 (PD-L1) expression in melanoma. Because gliomas can express PD-L1 causing a defective host anti-tumoral immunity, we investigated whether FKBP51s was expressed in glioma and played a role in PD-L1 regulation in this tumour. METHODS: We used D54 and U251 glioblastoma cell lines that constitutively expressed PD-L1. FKBP51s was measured by immunoblot, flow cytometry and microscopy. In patient tumours, IHC and qPCR were used to measure protein and mRNA levels respectively. FKBP51s depletion was achieved by siRNAs, and its enzymatic function was inhibited using selective inhibitors (SAFit). We investigated protein maturation using N-glycosidase and cell fractionation approaches. RESULTS: FKBP51s was expressed at high levels in glioma cells. Glycosylated-PD-L1 was increased and reduced by FKBP51s overexpression or silencing, respectively. Naïve PD-L1 was found in the endoplasmic reticulum (ER) of glioma cells complexed with FKBP51s, whereas the glycosylated form was measured in the Golgi apparatus. SAFit reduced PD-L1 levels (constitutively expressed and ionizing radiation-induced). SAFit reduced cell death of PBMC co-cultured with glioma. CONCLUSIONS: Here we addressed the mechanism of post-translational regulation of PD-L1 protein in glioma. FKBP51s upregulated PD-L1 expression on the plasma membrane by catalysing the protein folding required for subsequent glycosylation. Inhibition of FKBP51s isomerase activity by SAFit decreased PD-L1 levels. These findings suggest that FKBP51s is a potential target of immunomodulatory strategies for glioblastoma treatment.

FKBP51s signature in peripheral blood mononuclear cells of melanoma patients as a possible predictive factor for immunotherapy.

The inhibitory immune checkpoint PD-L1/PD1 promotes the alternative splicing of the FKBP5 gene, resulting in increased expression of its variant 4 in the peripheral blood mononuclear cells of melanoma patients. The variant 4 transcript is translated into the truncated FKBP51s protein. Given the importance of co-inhibitory signalling in tumour immune escape, here we tested the potential for using FKBP51s expression to predict immunotherapy outcomes. To do this, we immunophenotyped PBMCs from 118 melanoma patients and 77 age- and sex-matched healthy controls. Blood samples were collected before patients underwent ipilimumab treatment. In 64 of the 118 patients, FKBP51s expression was also assessed in regulatory T cells (Tregs). We found that each PBMC subset analysed contained an FKBP51spos fraction, and that this fraction was greater in the melanoma patients than healthy controls. In CD4 T lymphocytes, the FKBP51sneg fraction was significantly impaired. Tregs count was increased in melanoma patients, which is in line with previous studies. Also, by analyses of FKBP51s in Tregs, we identified a subgroup of ipilimumab nonresponder patients (p = 0.002). In conclusion, FKBP51s-based immunophenotyping of melanoma patients revealed several profiles related to a negative immune regulatory control and identified an unknown Treg subset. These findings are likely to be useful in the selection of the patients that are candidate for immunotherapy.

FKBP51 Immunohistochemical Expression: A New Prognostic Biomarker for OSCC?

Up-to-date, several molecular markers of prognosis have been studied in Oral Squamous Cell Carcinoma (OSCC), but none entered in the clinical setting. Therapy of OSCC tumors mainly relies on surgery, radiotherapy and partially on chemotherapy; there is an urgent need for biomarkers able to better stratify OSCC patients' risk to address targeted therapeutic strategies. The role of immune response in the pathogenesis and biological behavior of OSCC has been investigated by several authors, and promising results have been obtained with immune checkpoint inhibitors. We already investigated the role of the immune modulator FK506-binding protein 51 (FKBP51), a FK506-binding immunophilin, in cutaneous melanoma biology, and its expression in several human solid tumors. In the present study, we aimed to assess the value of FKBP51 expression in OSCC tumor cells as a marker of outcome. We collected clinical data from 72 patients who underwent surgery for Squamous Cell Carcinoma (SCC) of the tongue, floor, lips and palate. FKBP51 expression was assessed by immunohistochemistry on paraffin-embedded tumor tissues. In addition, we evaluated the human papillomavirus (HPV) status of primary tumors by immunohistochemistry, viral subtyping and In Situ Hybridization (ISH) assay. We found that high FKBP51-expressing tumors characterized the OSCCs with the worst prognosis: the high immunohistochemical expression of FKBP51 associated with death occurring within five years from the diagnosis with a sensitivity of 88.46% and a specificity of 91.67%. The estimated positive predictive value of the test was 88.45% and negative predictive value 91.67%. We tested FKBP51 mRNA presence, by RT-PCR assay, in a selected series of OSCC tumors, and we found that mRNA correlated well to the protein expression and to the clinical outcome. Applying the Bayes formula, we estimated an 88% probability of dying within five years from the diagnosis of OSCC patients with a high FKBP51 immunohistochemical (IHC) test result (>51% of FKBP51 positive tumor cells). On the basis of our analysis, we propose tumor tissue expression of FKBP51 protein as a reliable prognostic marker for OSCC tumors.