CD5-CK2 Signaling Modulates Erk Activation and Thymocyte Survival

CK2: The master regulator in tumor immune-microenvironment - A crucial target in oncotherapy

A constitutively active serine/threonine kinase, casein kinase 2 (CK2) is involved in several physiological functions, such as DNA repair, apoptosis, and cell cycle control. New research emphasizes how critical CK2 is to the immune system's dysregulation in the tumor immune-microenvironment (TIME). The inhibition of immunological responses, including the downregulation of immune effector cells and the elevation of immunosuppressive proteins that aid in the development of tumor and immune evasion, has been linked to CK2 overexpression. CK2 maintains an immunosuppressive milieu that impedes anti-tumor immunity by encouraging the expressions and activities of immune checkpoint markers, regulating cytokines release, and boosting immune-suppressive cells such as regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) to maintain immune evasion. It is a promising target for cancer treatment due to its complex role in immune regulation and oncogenic pathways. In this study, we address the therapeutic perspectives of targeting CK2 in oncotherapy and investigate the mechanisms by which it controls immunological responses in the TME. This review, comprehending the function of CK2 in immune suppression can facilitate the creation of innovative treatment approaches aimed at augmenting anti-tumor immunity and enhancing immunotherapy effectiveness.

Benzo[a]pyrene exposure causes exonal switch resulting in reduced surface CD5 expression in an AHR-dependent manner

The function of CD5 protein in T cells is well documented, but regulation of its surface-level expression has yet to be fully understood. However, variation in its surface expression is associated with various immunopathological conditions and haematological malignancies. Briefly, expression of an alternate exon E1B of a human endogenous retroviruses (HERV) origin directly downregulates the conventional transcript variant (E1A), as its expression leads to the retention of the resultant protein at the intracellular level (cCD5). A separate promoter governs the expression of E1B and may be influenced by different transcription factors. Hence, we performed in silico transcription factor binding site (TFBS) analysis of the 3 kb upstream region from TSS of exon E1B and found five putative DREs (Dioxin Response elements) with good similarity scores. Further, we observed the upregulation in E1B expression after the exposure of BaP (a dioxin) and the reduction of E1A expression and their respective protein, i.e. sCD5 and cCD5. The binding of AHR at the predicted DRE sites was confirmed by ChIP qPCR and AHR specific inhibitor and gene silencing studies suggested the involvement of AHR in exonal switch. This study indicates that the polycyclic aromatic hydrocarbon decreases the sCD5 expression by upregulating alternative exon expression, which may adversely affect the overall T cell functions.

Themis controls T cell activation, effector functions, and metabolism of peripheral CD8+ T cells

Themis is important in regulating positive selection of thymocytes during T cell development, but its role in peripheral T cells is less understood. Here, we investigated T cell activation and its sequelae using a tamoxifen-mediated, acute Themis deletion mouse model. We find that proliferation, effector functions including anti-tumor killing, and up-regulation of energy metabolism are severely compromised. This study reveals the phenomenon of peripheral adaptation to loss of Themis, by demonstrating direct TCR-induced defects after acute deletion of Themis that were not evident in peripheral T cells chronically deprived of Themis in dLck-Cre deletion model. Peripheral adaptation to long-term loss was compared using chronic versus acute tamoxifen-mediated deletion and with the (chronic) dLck-Cre deletion model. We found that upon chronic tamoxifen-mediated Themis deletion, there was modulation in the gene expression profile for both TCR and cytokine signaling pathways. This profile overlapped with (chronic) dLck-Cre deletion model. Hence, we found that peripheral adaptation induced changes to both TCR and cytokine signaling modules. Our data highlight the importance of Themis in the activation of CD8+ T cells.

Influence of Auditory Integrative Training on Casein Kinase 2 and Its Impact on Behavioral and Social Interaction in Children with Autism Spectrum Disorder

Considerable disturbances in post-translational protein phosphorylation have recently been discovered in multiple neurological disorders. Casein kinase-2 (CK2) is a tetrameric Ser/Thr protein kinase that phosphorylates a large number of substrates and contributes in several cellular physiological and pathological processes. CK2 is highly expressed in the mammalian brain and catalyzes the phosphorylation of a large number of substrates that are crucial in neuronal or glial homeostasis and inflammatory signaling processes across synapses. In this study, we investigated the impact of auditory integration therapy (AIT) for the treatment of sensory processing abnormalities in autism on plasma CK2 levels. A total of 25 ASD children, aged between 5 and 12 years, were enrolled and participated in the present research study. AIT was performed for two weeks, for a period of 30 min, twice a day, with a 3 h interval between sessions. Before and after AIT, the Childhood Autism Rating Scale (CARS), Social Responsiveness Scale (SRS), and Short Sensory Profile (SSP) scores were calculated, and plasma CK2 levels were assayed using an ELISA test. The CARS and SRS indices of autism severity improved as a result of AIT, which could be related to the decreased level of plasma CK2. However, the mean value of the SSP scores was not significantly increased after AIT. The relationship between CK2 downregulation and glutamate excitotoxicity, neuro-inflammation, and leaky gut, as etiological mechanisms in ASD, was proposed and discussed. Further research, conducted on a larger scale and with a longer study duration, are required to assess whether the cognitive improvement in ASD children after AIT is related to the downregulation of CK2.

Metabolic activation of tachysterol3 to biologically active hydroxyderivatives that act on VDR, AhR, LXRs, and PPARγ receptors

CYP11A1 and CYP27A1 hydroxylate tachysterol3 , a photoproduct of previtamin D3 , producing 20S-hydroxytachysterol3 [20S(OH)T3 ] and 25(OH)T3 , respectively. Both metabolites were detected in the human epidermis and serum. Tachysterol3 was also detected in human serum at a concentration of 7.3 ± 2.5 ng/ml. 20S(OH)T3 and 25(OH)T3 inhibited the proliferation of epidermal keratinocytes and dermal fibroblasts and stimulated the expression of differentiation and anti-oxidative genes in keratinocytes in a similar manner to 1,25-dihydroxyvitamin D3 [1,25(OH)2 D3 ]. They acted on the vitamin D receptor (VDR) as demonstrated by image flow cytometry and the translocation of VDR coupled GFP from the cytoplasm to the nucleus of melanoma cells, as well as by the stimulation of CYP24A1 expression. Functional studies using a human aryl hydrocarbon receptor (AhR) reporter assay system revealed marked activation of AhR by 20S(OH)T3 , a smaller effect by 25(OH)T3 , and a minimal effect for their precursor, tachysterol3 . Tachysterol3 hydroxyderivatives showed high-affinity binding to the ligan-binding domain (LBD) of the liver X receptor (LXR) α and β, and the peroxisome proliferator-activated receptor γ (PPARγ) in LanthaScreen TR-FRET coactivator assays. Molecular docking using crystal structures of the LBDs of VDR, AhR, LXRs, and PPARγ revealed high docking scores for 20S(OH)T3 and 25(OH)T3 , comparable to their natural ligands. The scores for the non-genomic-binding site of the VDR were very low indicating a lack of interaction with tachysterol3 ligands. Our identification of endogenous production of 20S(OH)T3 and 25(OH)T3 that are biologically active and interact with VDR, AhR, LXRs, and PPARγ, provides a new understanding of the biological function of tachysterol3 .

The three as: Alternative splicing, alternative polyadenylation and their impact on apoptosis in immune function

The latest advances in next-generation sequencing studies and transcriptomic profiling over the past decade have highlighted a surprising frequency of genes regulated by RNA processing mechanisms in the immune system. In particular, two control steps in mRNA maturation, namely alternative splicing and alternative polyadenylation, are now recognized to occur in the vast majority of human genes. Both have the potential to alter the identity of the encoded protein, as well as control protein abundance or even protein localization or association with other factors. In this review, we will provide a summary of the general mechanisms by which alternative splicing (AS) and alternative polyadenylation (APA) occur, their regulation within cells of the immune system, and their impact on immunobiology. In particular, we will focus on how control of apoptosis by AS and APA is used to tune cell fate during an immune response.

Vitamin D and lumisterol derivatives can act on liver X receptors (LXRs)

The interactions of derivatives of lumisterol (L3) and vitamin D3 (D3) with liver X receptors (LXRs) were investigated. Molecular docking using crystal structures of the ligand binding domains (LBDs) of LXRα and β revealed high docking scores for L3 and D3 hydroxymetabolites, similar to those of the natural ligands, predicting good binding to the receptor. RNA sequencing of murine dermal fibroblasts stimulated with D3-hydroxyderivatives revealed LXR as the second nuclear receptor pathway for several D3-hydroxyderivatives, including 1,25(OH)2D3. This was validated by their induction of genes downstream of LXR. L3 and D3-derivatives activated an LXR-response element (LXRE)-driven reporter in CHO cells and human keratinocytes, and by enhanced expression of LXR target genes. L3 and D3 derivatives showed high affinity binding to the LBD of the LXRα and β in LanthaScreen TR-FRET LXRα and β coactivator assays. The majority of metabolites functioned as LXRα/β agonists; however, 1,20,25(OH)3D3, 1,25(OH)2D3, 1,20(OH)2D3 and 25(OH)D3 acted as inverse agonists of LXRα, but as agonists of LXRβ. Molecular dynamics simulations for the selected compounds, including 1,25(OH)2D3, 1,20(OH)2D3, 25(OH)D3, 20(OH)D3, 20(OH)L3 and 20,22(OH)2L3, showed different but overlapping interactions with LXRs. Identification of D3 and L3 derivatives as ligands for LXRs suggests a new mechanism of action for these compounds.

CD5 and CD6 as immunoregulatory biomarkers in non-small cell lung cancer

BACKGROUND

The study of immune surveillance in the tumour microenvironment is leading to the development of new biomarkers and therapies. The present research focuses on the expression of CD5 and CD6-two lymphocyte surface markers involved in the fine tuning of TCR signaling-as potential prognostic biomarkers in resectable stages of non-small cell lung cancer (NSCLC).

METHODS

CD5 and CD6 gene expression was analysed by reverse transcription quantitative polymerase chain reaction (RTqPCR) in 186 paired fresh frozen tumour and normal tissue samples of resected NSCLC.

RESULTS

Patients with higher CD5 expression had significantly increased overall survival (OS, 49.63 vs. 99.90 months, P=0.013). CD5 expression levels were correlated to CD4 infiltration and expression levels, and survival analysis showed that patients with a higher CD5/CD4 + ratio had significantly improved prognosis. Multivariate analysis established CD5 expression as an independent prognostic biomarker for OS in early stages of NSCLC (HR=0.554; 95% CI, 0.360-0.853; P=0.007). Further survival analysis of NSCLC cases (n=97) from The Cancer Genome Atlas (TCGA) database, confirmed the prognostic value of both CD5 and CD6 expression¸ although CD6 expression alone did not reach significant prognostic value in our NSCLC training cohort.

CONCLUSIONS

Our data support further studies on CD5 and CD6 as novel prognostic markers in resectable NSCLC and other cancer types (i.e., melanoma), as well as a role for these receptors in immune surveillance.

CD5 dynamically calibrates basal NF-κB signaling in T cells during thymic development and peripheral activation

Immature T cells undergo a process of positive selection in the thymus when their new T cell receptor (TCR) engages and signals in response to self-peptides. As the T cell matures, a slew of negative regulatory molecules, including the inhibitory surface glycoprotein CD5, are up-regulated in proportion to the strength of the self-peptide signal. Together these regulators dampen TCR-proximal signaling and help avoid any subsequent peripheral activation of T cells by self-peptides. Paradoxically, antigen-specific T cells initially expressing more CD5 (CD5^hi) have been found to better persist as effector/memory cells after a peripheral challenge. The molecular mechanisms underlying such a duality in CD5 function is not clear. We found that CD5 alters the basal activity of the NF-κB signaling in resting peripheral T cells. When CD5 was conditionally ablated, T cells were unable to maintain higher expression of the cytoplasmic NF-κB inhibitor IκBα. Consistent with this, resting CD5^hi T cells expressed more of the NF-κB p65 protein than CD5^lo cells, without significant increases in transcript levels, in the absence of TCR signals. This posttranslationally stabilized cellular NF-κB depot potentially confers a survival advantage to CD5^hi T cells over CD5^lo ones. Taken together, these data suggest a two-step model whereby the strength of self-peptide-induced TCR signal lead to the up-regulation of CD5, which subsequently maintains a proportional reserve of NF-κB in peripheral T cells poised for responding to agonistic antigen-driven T cell activation.

Photoprotective Properties of Vitamin D and Lumisterol Hydroxyderivatives

We have previously described new pathways of vitamin D3 activation by CYP11A1 to produce a variety of metabolites including 20(OH)D3 and 20,23(OH)2D3. These can be further hydroxylated by CYP27B1 to produce their C1α-hydroxyderivatives. CYP11A1 similarly initiates the metabolism of lumisterol (L3) through sequential hydroxylation of the side chain to produce 20(OH)L3, 22(OH)L3, 20,22(OH)2L3 and 24(OH)L3. CYP11A1 also acts on 7-dehydrocholesterol (7DHC) producing 22(OH)7DHC, 20,22(OH)27DHC and 7-dehydropregnenolone (7DHP) which can be converted to the D3 and L3 configurations following exposure to UVB. These CYP11A1-derived compounds are produced in vivo and are biologically active displaying anti-proliferative, anti-inflammatory, anti-cancer and pro-differentiation properties. Since the protective role of the classical form of vitamin D3 (1,25(OH)2D3) against UVB-induced damage is recognized, we recently tested whether novel CYP11A1-derived D3- and L3-hydroxyderivatives protect against UVB-induced damage in epidermal human keratinocytes and melanocytes. We found that along with 1,25(OH)2D3, CYP11A1-derived D3-hydroxyderivatives and L3 and its hydroxyderivatives exert photoprotective effects. These included induction of intracellular free radical scavenging and attenuation and repair of DNA damage. The protection of human keratinocytes against DNA damage included the activation of the NRF2-regulated antioxidant response, p53-phosphorylation and its translocation to the nucleus, and DNA repair induction. These data indicate that novel derivatives of vitamin D3 and lumisterol are promising photoprotective agents. However, detailed mechanisms of action, and the involvement of specific nuclear receptors, other vitamin D binding proteins or mitochondria, remain to be established.

Extra-adrenal glucocorticoid biosynthesis: implications for autoimmune and inflammatory disorders

Glucocorticoid synthesis is a complex, multistep process that starts with cholesterol being delivered to the inner membrane of mitochondria by StAR and StAR-related proteins. Here its side chain is cleaved by CYP11A1 producing pregnenolone. Pregnenolone is converted to cortisol by the enzymes 3-βHSD, CYP17A1, CYP21A2 and CYP11B1. Glucocorticoids play a critical role in the regulation of the immune system and exert their action through the glucocorticoid receptor (GR). Although corticosteroids are primarily produced in the adrenal gland, they can also be produced in a number of extra-adrenal tissue including the immune system, skin, brain, and intestine. Glucocorticoid production is regulated by ACTH, CRH, and cytokines such as IL-1, IL-6 and TNFα. The bioavailability of cortisol is also dependent on its interconversion to cortisone which is inactive, by 11βHSD1/2. Local and systemic glucocorticoid biosynthesis can be stimulated by ultraviolet B, explaining its immunosuppressive activity. In this review, we want to emphasize that dysregulation of extra-adrenal glucocorticoid production can play a key role in a variety of autoimmune diseases including multiple sclerosis (MS), lupus erythematosus (LE), rheumatoid arthritis (RA), and skin inflammatory disorders such as psoriasis and atopic dermatitis (AD). Further research on local glucocorticoid production and its bioavailability may open doors into new therapies for autoimmune diseases.

CD5 blockade enhances ex vivo CD8+ T cell activation and tumour cell cytotoxicity

CD5 is expressed on T cells and a subset of B cells (B1a). It can attenuate TCR signalling and impair CTL activation and is a therapeutic targetable tumour antigen expressed on leukemic T and B cells. However, the potential therapeutic effect of functionally blocking CD5 to increase T cell anti-tumour activity against tumours (including solid tumours) has not been explored. CD5 knockout mice show increased anti-tumour immunity: reducing CD5 on CTLs may be therapeutically beneficial to enhance the anti-tumour response. Here, we show that ex vivo administration of a function-blocking anti-CD5 MAb to primary mouse CTLs of both tumour-naïve mice and mice bearing murine 4T1 breast tumour homografts enhanced their capacity to respond to activation by treatment with anti-CD3/anti-CD28 MAbs or 4T1 tumour cell lysates. Furthermore, it enhanced TCR signalling (ERK activation) and increased markers of T cell activation, including proliferation, CD69 levels, IFN-γ production, apoptosis and Fas receptor and Fas ligand levels. Finally, CD5 function-blocking MAb treatment enhanced the capacity of CD8⁺ T cells to kill 4T1-mouse tumour cells in an ex vivo assay. These data support the potential of blockade of CD5 function to enhance T cell-mediated anti-tumour immunity.

The multiple faces of CD5

Since its discovery, over 30 years ago, CD5 has been used as a marker to identify T cells, B1-a cells, and B cell chronic lymphocytic leukemia cells. Throughout the years, many studies have described the functional relevance of CD5 as a modulator of T and B cell receptor signaling. However, it has not been until recent years that CD5 has emerged as a functional receptor in other areas of the immune system. Here, we review some of the most important aspects of CD5 as a modulator of TCR and BCR signaling, cell survival receptor both in T and B cells during health and disease, as well as the newly discovered roles of this receptor in thymocyte selection, T cell effector differentiation, and immune tolerance. CD5 was found to promote T cell survival by protecting autoreactive T cell from activation-induced cell death, to promote de novo induction of regulatory T cells in the periphery, to modulate Th17 and Th2 differentiation, and to modulate immune responses by modulating dendritic cell functions. CD5 is overexpressed in Tregs and Bregs, which are fundamental to maintain immune homeostasis. The newly established roles of CD5 in modulating different aspects of immune responses identify this receptor as an immune checkpoint modulator, and therefore it could be used as a target for immune intervention in different pathologies such as cancer, autoimmune diseases or infections.

Inhibition of Casein Kinase 2 Protects Oligodendrocytes From Excitotoxicity by Attenuating JNK/p53 Signaling Cascade

Oligodendrocytes are highly vulnerable to glutamate excitotoxicity, a central mechanism involved in tissue damage in Multiple Sclerosis (MS). Sustained activation of AMPA receptors in rat oligodendrocytes induces cytosolic calcium overload, mitochondrial depolarization, increase of reactive oxygen species, and activation of intracelular pathways resulting in apoptotic cell death. Although many signals driven by excitotoxicity have been identified, some of the key players are still under investigation. Casein kinase 2 (CK2) is a serine/threonine kinase, constitutively expressed in all eukaryotic tissues, involved in cell proliferation, malignant transformation and apoptosis. In this study, we identify CK2 as a critical regulator of oligodendrocytic death pathways and elucidate its role as a signal inductor following excitotoxic insults. We provide evidence that CK2 activity is up-regulated in AMPA-treated oligodendrocytes and CK2 inhibition significantly diminished AMPA receptor-induced oligodendroglial death. In addition, we analyzed mitogen-activated protein kinase (MAPK) signaling after excitotoxic insult. We observed that AMPA receptor activation induced a rapid increase in c-Jun N-terminal kinase (JNK) and p38 phosphorylation that was reduced after CK2 inhibition. Moreover, blocking their phosphorylation, we enhanced oligodendrocyte survival after excitotoxic insult. Finally, we observed that the tumor suppressor p53 is activated during AMPA receptor-induced cell death and, interestingly, down-regulated by JNK or CK2 inhibition. Together, these data indicate that the increase in CK2 activity induced by excitotoxic insults regulates MAPKs, triggers p53 activation and mediates subsequent oligodendroglial loss. Therefore, targeting CK2 may be a useful strategy to prevent oligodendrocyte death in MS and other diseases involving central nervous system (CNS) white matter.