Heterogeneous expression of predictive biomarkers PD-L1 and TIGIT in non-mucinous lung adenocarcinoma and corresponding lymph node metastasis: A challenge for clinical biomarker testing.

The use of immune checkpoint inhibitors (ICI) targeting the PD-L1:PD1 interaction revolutionized tumor treatment by re-activating the anti-tumoral capacity of the immune system. Assessment of tumor mutational burden, microsatellite instability, or expression of the surface marker PD-L1 have been used to predict individual response to ICI therapy. However, the predicted response does not always correspond to the actual therapy outcome. We hypothesize that tumor heterogeneity might be a major cause of this inconsistency. In this respect we recently demonstrated that PD-L1 shows heterogenous expression in the different growth patterns of non-small cell lung cancer (NSCLC) - lepidic, acinar, papillary, micropapillary and solid. Furthermore, additional inhibitory receptors, like T cell immunoglobulin and ITIM domain (TIGIT), appear to be heterogeneously expressed and affect the outcome of anti-PD-L1 treatment. Given this heterogeneity in the primary tumor, we set out to analyze the situation in corresponding lymph node metastases, since these are often used to obtain biopsy material for tumor diagnosis, staging and molecular analysis. Again, we observed heterogeneous expression of PD-1, PD-L1, TIGIT, Nectin-2 and PVR in relation to different regions and growth pattern distribution that varied between the primary tumor and their metastases. Together, our study underscores the complex situation regarding the heterogeneity of NSCLC samples and suggest that the analysis of a small biopsy from lymph node metastases may not be sufficient to ensure a reliable prediction of ICI therapy success.

Patterns of antibody responses to nonviral cancer antigens in head and neck squamous cell carcinoma patients differ by human papillomavirus status.

There have been hints that nonviral cancer antigens are differentially expressed in human papillomavirus (HPV)-positive and HPV-negative head and neck squamous cell carcinoma (HNSCC). Antibody responses (AR) to cancer antigens may be used to indirectly determine cancer antigen expression in the tumor using a noninvasive and tissue-saving liquid biopsy. Here, we set out to characterize AR to a panel of nonviral cancer antigens in HPV-positive and HPV-negative HNSCC patients. A fluorescent microbead multiplex serology to 29 cancer antigens (16 cancer-testis antigens, 5 cancer-retina antigens and 8 oncogenes) and 29 HPV-antigens was performed in 382 HNSCC patients from five independent cohorts (153 HPV-positive and 209 HPV-negative). AR to any of the cancer antigens were found in 272/382 patients (72%). The ten most frequent AR were CT47, cTAGE5a, c-myc, LAGE-1, MAGE-A1, -A3, -A4, NY-ESO-1, SpanX-a1 and p53. AR to MAGE-A3, MAGE-A9 and p53 were found at significantly different prevalences by HPV status. An analysis of AR mean fluorescent intensity values uncovered remarkably different AR clusters by HPV status. To identify optimal antigen selections covering a maximum of patients with ≤10 AR, multiobjective optimization revealed distinct antigen selections by HPV status. We identified that AR to nonviral antigens differ by HPV status indicating differential antigen expression. Multiplex serology may be used to characterize antigen expression using serum or plasma as a tissue-sparing liquid biopsy. Cancer antigen panels should address the distinct antigen repertoire of HPV-positive and HPV-negative HNSCC.

GSK3ß modulates NF-κB activation and RelB degradation through site-specific phosphorylation of BCL10.

Glycogen synthase kinase 3ß (GSK3ß) is a ubiquitously expressed serine/threonine kinase involved in the regulation of various cellular functions, such as energy homoeostasis, cell growth and developmental processes. More recently, GSK3ß has been identified as a part of a protein complex involved in the regulation of the CARMA1-BCL10-MALT1 complex (CBM complex) formation, which is a key signalling event upon antigen receptor engagement of B and T cells, required for the activation of the NF-κB and JNK pathways. However, conflicting reports have been published regarding the role of GSK3ß for the activation of the NF-κB signalling pathways. Therefore, we aimed to determine the impact of GSK3ß on the NF-κB signalling induced upon T cell activation. Blocking GSK3ß by either pharmacologic inhibitors (SB216763 and SB415286) or by RNAi caused a reduced proteolysis of the MALT1 targets CYLD1, BCL10 and RelB as well as diminished IκBα degradation, NF-κB DNA binding and NF-κB activity. This negative effect on NF-κB appears to be due to a diminished CBM complex formation caused by a reduced BCL10 phosphorylation. Taken together, we provide here evidence for a novel regulatory mechanism by which GSK3ß affects NF-κB signalling in activated T cells.

SUMOylation attenuates the transcriptional activity of the NF-κB subunit RelB.

The NF-κB subunit RelB is known to act either as an activator or repressor of NF-κB-dependent gene expression. The RelB-p52 heterodimer, for instance, is the key element of the alternative NF-κB signaling pathway supporting the expression of a subset of NF-κB target genes. By contrast, RelB is crucial for the repression of important pro-inflammatory cytokines like TNFα or interleukin 1ß. Despite accumulating reports describing the functional variability of RelB, the molecular mechanisms underlying these divergent functions are still unknown. One potential explanation could be a functional reprogramming of RelB by different post-translational modifications. Here, we demonstrate that SUMOylation of RelB might be one of these post-translational modifications rendering the function of the NF-κB transcription factor RelB. In vivo SUMOylation analyses using either the UBC9-fusion-directed SUMOylation method or endogenous proteins from Namalwa B cells revealed that RelB is modified by either SUMO1 or SUMO2 attachment at various sites. Functional studies suggest that SUMOylation converts RelB into a transcriptional repressor. For instance, a SUMO1-RelB fusion protein mimicking RelB-SUMOylation displayed a reduced transcriptional activity in comparison to wild type RelB. Consistently, inactivation of specific SUMOylation sites in the central part of RelB augmented the transcription activity of the corresponding RelB mutant. Taken together, our data suggest that SUMOylation might be a potential molecular mechanism involved in reprogramming RelB, thus contributing to its functional diversity.

Octamer-dependent transcription in T cells is mediated by NFAT and NF-κB.

The transcriptional co-activator BOB.1/OBF.1 was originally identified in B cells and is constitutively expressed throughout B cell development. BOB.1/OBF.1 associates with the transcription factors Oct1 and Oct2, thereby enhancing octamer-dependent transcription. In contrast, in T cells, BOB.1/OBF.1 expression is inducible by treatment of cells with PMA/Ionomycin or by antigen receptor engagement, indicating a marked difference in the regulation of BOB.1/OBF.1 expression in B versus T cells. The molecular mechanisms underlying the differential expression of BOB.1/OBF.1 in T and B cells remain largely unknown. Therefore, the present study focuses on mechanisms controlling the transcriptional regulation of BOB.1/OBF.1 and Oct2 in T cells. We show that both calcineurin- and NF-κB-inhibitors efficiently attenuate the expression of BOB.1/OBF.1 and Oct2 in T cells. In silico analyses of the BOB.1/OBF.1 promoter revealed the presence of previously unappreciated combined NFAT/NF-κB sites. An array of genetic and biochemical analyses illustrates the involvement of the Ca(2+)/calmodulin-dependent phosphatase calcineurin as well as NFAT and NF-κB transcription factors in the transcriptional regulation of octamer-dependent transcription in T cells. Conclusively, impaired expression of BOB.1/OBF.1 and Oct2 and therefore a hampered octamer-dependent transcription may participate in T cell-mediated immunodeficiency caused by the deletion of NFAT or NF-κB transcription factors.

IκB kinases modulate the activity of the androgen receptor in prostate carcinoma cell lines.

Enhanced nuclear localization of nuclear factor κB (NF-κB) in prostate cancer (PCa) samples and constitutive NF-κB signaling in a class of PCa cell lines with low androgen receptor (AR) expression (PC3 and DU-145) imply an important role of the IκB kinase (IKK)/NF-κB system in PCa. However, most PCa and PCa cell lines depend on the activity of the AR, and the role of NF-κB in these AR-expressing PCa remains unclear. Here, we demonstrate that inhibition of NF-κB signaling by the IKK inhibitor BMS345541 reduced proliferation and increased apoptosis in AR-expressing PCa cell lines. Furthermore, AR activity and target gene expression were distinctively reduced, whereas AR protein levels remained unaltered on BMS345541 treatment. Similar effects were observed particularly after small interfering RNA (siRNA)-mediated knockdown of IKK1, but not by siRNA-mediated suppression of IKK2. Moreover, IKK1 overexpression augmented 5α-dihydrotestosterone-induced nuclear AR translocation, whereas nuclear AR was reduced by IKK1 knockdown or BMS345541. However, because IKK1 also enhances the activity of a chronically nuclear AR mutant, modulation of the subcellular distribution seems not to be the only mechanism by which IKK1 enhances AR activity. Finally, reduced in vivo AR phosphorylation after BMS345541 treatment and in vitro AR phosphorylation by IKK1 or IKK2 imply that AR constitutes a novel IKK target. Taken together, our data identify IKK1 as a potentially target structure for future therapeutic intervention in PCa.

NF-κB signaling in prostate cancer: a promising therapeutic target?

Prostate carcinoma (PCa) displays a wide variety of genetic alterations, versatile expression profiles as well as cell surface markers. Despite this heterogeneity, a common treatment for advanced PCa is androgen deprivation therapy (ADT). ADT targets the androgen receptor-a member of the nuclear receptor superfamily-which is required for development and function of the prostate and critical for PCa growth and survival. After an initial regression of the tumor during ADT, a large fraction of tumors progress to so-called castration-resistant prostate carcinoma (CRPca) which is highly resistant toward chemotherapy. The ensuing high mortality rates illustrate the importance of novel therapeutic targets for CRPCa. The transcription factor NF-κB was recently proposed as such a potential target for therapeutic intervention in CRPCa. Although NF-κB is essential for the regulation of innate and adaptive immunity recent data suggest a role of NF-κB in cancer initiation and progression. However, the exact function of NF-κB signaling in PCa is still a matter of debate. Here, we review known roles of NF-κB signaling in PCa and emphasize the crosstalk of NF-κB and androgen receptor signaling. Finally, we discuss potential therapeutic relevance of blocking NF-κB in PCa.

The Ca2+-dependent phosphatase calcineurin controls the formation of the Carma1-Bcl10-Malt1 complex during T cell receptor-induced NF-kappaB activation.

T cell receptor (TCR) ligation induces increased diacylglycerol and Ca(2+) levels in T cells, and both secondary messengers are crucial for TCR-induced nuclear factor of activated T cells (NF-AT) and NF-κB signaling pathways. One prominent calcium-dependent enzyme involved in the regulation of NF-AT and NF-κB signaling pathways is the protein phosphatase calcineurin. However, in contrast to NF-AT, which is directly dephosphorylated by calcineurin, the molecular basis of the calcium-calcineurin dependence of the TCR-induced NF-κB activity remains largely unknown. Here, we demonstrate that calcineurin regulates TCR-induced NF-κB activity by controlling the formation of a protein complex composed of Carma1, Bcl10, and Malt1 (CBM complex). For instance, increased calcium levels induced by ionomycin or thapsigargin augmented the phorbol 12-myristate 13-acetate-induced formation of the CBM complex and activation of NF-κB, whereas removal of calcium by the calcium chelator EGTA-acetoxymethyl ester (AM) attenuated both processes. Furthermore, inhibition of the calcium-dependent phosphatase calcineurin with the immunosuppressive agent cyclosporin A (CsA) or FK506 as well as siRNA-mediated knockdown of calcineurin A strongly affected the PMA + ionomycin- or anti-CD3 + CD28-induced CBM complex assembly. Mechanistically, the positive effect of calcineurin on the CBM complex formation seems to be linked to a dephosphorylation of Bcl10. For instance, Bcl10 was found to be hyperphosphorylated in Jurkat T cells upon treatment with CsA or EGTA-AM, and calcineurin dephosphorylated Bcl10 in vivo and in vitro. Furthermore, we show here that calcineurin A interacts with the CBM complex. In summary, the evidence provided here argues for a previously unanticipated role of calcineurin in CBM complex formation as a molecular basis of the inhibitory function of CsA or FK506 on TCR-induced NF-κB activity.

Phosphorylation of serine 68 in the IkappaB kinase (IKK)-binding domain of NEMO interferes with the structure of the IKK complex and tumor necrosis factor-alpha-induced NF-kappaB activity.

The IkappaB-Kinase (IKK) complex is a multisubunit protein complex crucial for signal-induced phosphorylation of the IkappaB proteins and thus controls the activity of the transcription factor NF-kappaB. Besides the two kinases IKKalpha and IKKbeta, the IKK complex contains NEMO/IKKgamma, an additional subunit with regulatory and adaptor functions. NEMO not only confers structural stability to the IKK complex but also participates in the activation process of the IKK complex by linking the IKK subunits to upstream activators. In this study we analyze the IKKbeta-mediated phosphorylation of the IKK-binding domain of NEMO. In vitro, IKKbeta phosphorylates three serine residues in the domain of NEMO at positions 43, 68, and 85. However, mutational analysis revealed that only the phosphorylation of serine 68 in the center of the IKK-binding domain plays an essential role for the formation and the function of the IKK complex. Thus, Ser(68) phosphorylation attenuates the amino-terminal dimerization of NEMO as well as the IKKbeta-NEMO interaction. In contrast, the NEMO-IKKalpha interaction was only mildly affected by the phosphorylation of Ser(68). However, functional analysis revealed that Ser(68) phosphorylation primarily affects the activity of IKKalpha. Furthermore, in complementation experiments of NEMO-deficient murine embryonic fibroblasts, a S68A-NEMO mutant enhanced, whereas a S68E mutant decreased, TNF-alpha-induced NF-kappaB activity, thus emphasizing the inhibitory role of the Ser(68) phosphorylation on the signal-induced NF-kappaB activity. Finally, we provide evidence that the protein phosphatase PP2A is involved in the regulation of the Ser(68)-based mechanism. In summary, we provide evidence for a signal-induced phosphorylation-dependent alteration of the IKK complex emphasizing the dynamic nature of this multisubunit kinase complex.

Dimerization of the I kappa B kinase-binding domain of NEMO is required for tumor necrosis factor alpha-induced NF-kappa B activity.

Previous studies have demonstrated that peptides corresponding to a six-amino-acid NEMO-binding domain from the C terminus of IkappaB kinase alpha (IKKalpha) and IKKbeta can disrupt the IKK complex and block NF-kappaB activation. We have now mapped and characterized the corresponding amino-terminal IKK-binding domain (IBD) of NEMO. Peptides corresponding to the IBD were efficiently recruited to the IKK complex but displayed only a weak inhibitory potential on cytokine-induced NF-kappaB activity. This is most likely due to the formation of sodium dodecyl sulfate- and urea-resistant NEMO dimers through a dimerization domain at the amino terminus of NEMO that overlaps with the region responsible for binding to IKKs. Mutational analysis revealed different alpha-helical subdomains within an amino-terminal coiled-coil region are important for NEMO dimerization and IKKbeta binding. Furthermore, NEMO dimerization is required for the tumor necrosis factor alpha-induced NF-kappaB activation, even when interaction with the IKKs is unaffected. Hence, our data provide novel insights into the role of the amino terminus of NEMO for the architecture of the IKK complex and its activation.

Characterization of the Ikappa B-kinase NEMO binding domain.

Proinflammatory activation of NF-kappaB requires an upstream kinase complex (IkappaB-kinase; IKK) composed of two catalytic subunits (IKKalpha and IKKbeta) and a noncatalytic regulatory component named NEMO (NF-kappaB essential modulator). NEMO interacts with a COOH-terminal sequence within both IKKs termed the NEMO-binding domain (NBD), and a cell-permeable NBD peptide blocks NEMO/IKKbeta interactions and inhibits tumor necrosis factor-alpha-induced NF-kappaB. We report here that a peptide encompassing the NBD not only blocked association of both IKKs with NEMO but also disrupted preformed NEMO/IKK complexes in vitro. Furthermore, peptide blocking and alanine-scanning mutation studies revealed differences between the NBDs of IKKalpha and IKKbeta, and mutational analysis of the IKKbeta NBD identified the physical properties required at each position to maintain association with NEMO. Finally, we demonstrate that loss of NEMO-binding by IKKbeta through deletion of the NBD renders it catalytically active and that potential phosphorylation within the IKKbeta NBD may serve as a signal to down-regulate IKK activity. Our findings therefore provide critical insight into the physical properties of the NBD that will be valuable for the design of drugs aimed at disrupting the IKK complex and also reveal potential regulatory mechanisms controlling the function of the IKK complex.