Studies of calcineurin B subunit from genetic engineering for use in medicine

The immunostimulatory effects and pro-apoptotic activity of rhCNB against Lewis lung cancer is mediated by Toll-like receptor 4

Background

Recombinant human calcineurin B subunit (rhCNB) has been shown to be an immune‐stimulatory protein promoting cytokine production and inducing phenotypic maturation of Dendritic cells (DCs). In vivo, it has good antitumor efficacy, and has potential as an antitumor drug. Exogenous rhCNB was found to be internalized into tumor cells via the Toll‐like receptor 4 (TLR4) complex, but it was not known whether its immuno‐modulatory and antitumor functions involved entry by this same route.

Methods

The production and secretion of the cytokines and chemokines in innate immune cells induced by rhCNB were determined by ELISA, and the expression of CD40, CD80, CD86, and MHCII was analyzed by FACs. Experimental Lewis lung cancer (LLC) model was prepared in C57 BL/6 wild‐type (WT) mice, TLR4^−/− mice or their littermates by the inoculation of LLCs in their right armpit, and then administrated daily intraperitoneal injections (0.2 mL) of normal saline, rhCNB 20 mg/kg, and rhCNB 40 mg/kg, respectively.

Results

Recombinant human calcineurin B subunit promoted the production of antitumor cytokines by innate immune cells, and culture supernatants of rhCNB‐stimulated immune cells induced apoptosis of LLCs. In addition, rhCNB up‐regulated CD40, CD80, CD86, and MHCII expression in macrophages and DCs in TLR4⁺ cells but failed to do so in TLR4 deficient cells. rhCNB also induced the formation of CD4⁺ and CD8⁺T cells in splenocytes from WT mice, but not from TLR4‐deficient littermates. Intraperitoneal administration of WT C57BL/6 mice with rhCNB resulted in a 50% reduction in LLC tumor growth, but failed to inhibit tumor growth in TLR4^−/− littermates.

Conclusions

The in vivo antitumor and immunomodulatory effects of rhCNB are mediated by the TLR4. This conclusion is important for the further understanding and development of rhCNB as an antitumor drug.

Identification of a targeting-delivery peptide based on rhCNB

Calcineurin B subunit (CNB) is the regulatory subunit of calcineurin (CN), and its classical function is to regulate the activity of CN. Research in our laboratory has revealed that the recombinant human CNB (rhCNB) is a good antitumor candidate and can be internalized by tumor cells via TLR4 receptor complexes and targeted to tumor tissue in nude mice. However, the fragment or domain of rhCNB mediating internalization and target delivery has not been identified. To explore fragment- mediated rhCNB internalization and target delivery, we generated truncated derivatives of rhCNBs by recombinant DNA technology and examined their cellular uptake. Interactions between truncated rhCNBs and the TLR4 receptor were studied by ELISA and co-immunoprecipitation, and targeting of model tumors in nude mice was examined. The results showed that one truncated derivative, Trun3 (124-169aa), was taken up by cells and targeted tumors with almost the same efficiency as intact rhCNB. These results indicate that Trun3 (45aa) contains the major sequence responsible for rhCNB internalization and tumor targeting and might be developed for drug delivery to tumors.

The genetically engineered drug rhCNB induces apoptosis via a mitochondrial route in tumor cells

The calcineurin B subunit (CNB) has antitumor activity. We showed previously that recombinant human CNB (rhCNB) also had strong anti-tumor activity in vivo, and was thus a promising candidate anti-tumor drug. It appeared to kill tumor cells via immunomodulation. Here, we show that rhCNB inhibits the proliferation of human hepatoma HepG-2 cells, resulting in their apoptosis. Exogenous CNB was found to localize to mitochondria in tumor cells and activate the mitochondrial apoptosis pathway, as indicated by a decrease of mitochondrial transmembrane potential, release of cytochrome C and activation of caspase-9, which then activates caspase-3. At the same time Bcl-2 &Bcl-xL expression decreased, Bim expression increased, and Bax was activated. Interaction between rhCNB and Bcl-xL was detected, which may inhibit the function of Bcl-xL. Long-term tumor targeting was also observed in nude mice. These data deepened our understanding of the anti-tumor mechanism of rhCNB and provided guidance for its drug development.

Cellular uptake of exogenous calcineurin B is dependent on TLR4/MD2/CD14 complexes, and CnB is an endogenous ligand of TLR4

Our previous research showed that recombinant calcineurin B (rhCnB) stimulates cytokine secretion by immune cells, probably through TLR4. Exogenous CnB can be incorporated into many different tumour cells in vitro, but the mode of uptake and receptors required remain unknown. Here, we report that exogenous CnB is taken up by cells in a time- and concentration-dependent manner via clathrin-dependent receptor-mediated internalization. Our findings further confirm that uptake is mediated by the TLR4/MD2 complex together with the co-receptor CD14. The MST results revealed a high affinity between CnB and the TLR4 receptor complex. No binding was detected between CnB and LPS. CnB inhibited the uptake of LPS, and LPS also inhibited the uptake of CnB. These results indicate that the uptake of exogenous CnB did not occur through LPS and that CnB was not a chaperone of LPS. Thus, we conclude that TLR4 receptor complexes were required for the recognition and internalization of exogenous CnB. CnB could be a potential endogenous ligand of TLR4 and function as an agonist of TLR4. These properties of CnB support its potential for development as an anti-cancer drug.

Quality-control method for the determination of biological activity of engineered calcineurin subunit B

The aim of this study was to establish a quality-control method for calcineurin subunit B (CNB) biological activity determinations. CNB enhances the p-nitrophenylphosphate (pNPP) dephosphorylating activity of calcineurin subunit A Δ316 mutant (CNAΔ316). A series of CNB concentrations were fitted to a four-parameter equation to calculate the corresponding pNPP maximum dephosphorylation rates. Values were calculated based on biological activity references using a parallel line method. The method was then validated for accuracy, precision, linearity, linear range, sensitivity, specificity, and robustness. The recovery results were greater than 98%. Intra-plate precision was 6.7%, with inter-plate precision of 10.8%. The coefficient of determination was greater than 0.98. The linear range was 0.05-50 μg mL(-1), with sensitivity of 50 μg mL(-1). Tested cytokines did not induce CNAΔ316 dephosphorylation of pNPP. The chosen CNAΔ316 concentration range did not affect activity determinations.

Calcineurin B stimulates cytokine production through a CD14-independent Toll-like receptor 4 pathway

The calcineurin B subunit (CnB) is the regulatory subunit of Cn, a Ca(2+)/calmodulin-dependent serine/threonine protein phosphatase. In this study, we demonstrate that extracellular CnB was effectively internalized through a CD14-independent Toll-like receptor 4 (TLR4) pathway, which led to the phosphorylation of nuclear factor (NF)-kappa-B inhibitor alpha (IκB-α) and upregulation of pro-inflammatory cytokines in human monocytes. CnB-induced IκB-α phosphorylation is completely dependent on TNF receptor-associated factor 3 (TRAF3) but not TRAF6, which is indispensable for IκB-α phosphorylation in response to lipopolysaccharide. The loss-of-function CnB mutants were able to induce IκB-α phosphorylation, further indicating that this novel role of CnB is completely independent of the phosphatase function of Cn. Taken together, these findings demonstrate that CnB is a novel host-derived immunostimulatory factor, having a role as an agonist in monocytes, and specificity in TLR4 signaling through TRAF3 and TRAF6, in response to various agonists.

The synergistic interaction between the calcineurin B subunit and IFN-γ enhances macrophage antitumor activity

Macrophages are involved in tumor growth and progression. They infiltrate into tumors and cause inflammation, which creates a microenvironment favoring tumor growth and metastasis. However, certain stimuli may induce macrophages to act as tumor terminators. Here we report that the calcineurin B subunit (CnB) synergizes with IFN-γ to make macrophages highly cytotoxic to cancer cells. Furthermore, CnB and IFN-γ act synergistically to polarize mouse tumor-associated macrophages, as well as human monocyte-derived macrophages to an M1-like phenotype. This synergy is mediated by the crosstalk between CnB-engaged integrin αM-p38 MAPK signaling and IFN-γ-initiated p38/PKC-δ/Jak2 signaling. Interestingly, the signal transducer and activator of transcription 1 (STAT1) is a key factor that orchestrates the synergy of CnB and IFN-γ, and the phosphorylation status at Ser727 and Tyr701 of STAT1 is directly regulated by CnB and IFN-γ.

Calcineurin B subunit triggers innate immunity and acts as a novel Engerix-B HBV vaccine adjuvant

We showed previously that calcineurin B subunit (CnB) protein activates innate immune cells including macrophages, monocytes and dendritic cells and acts as an adjuvant of a model antigen (ovalbumin) and a recombinant pneumolysin antigen, but the detailed mechanism is not clear and whether it can serve as an adjuvant of a commercial HBV vaccine is unknown. Here, we report that CnB promotes inflammatory cytokines production, splenocytes proliferation and NK lytic activity, and that CnB-induced inflammatory cytokines (IFN-γ, IL-6, TNF-α) production is dependent on integrin αM. Animal experiments demonstrate that CnB markedly increases the total anti-HBs antibodies in a dose and time dependent manner. Furthermore, CnB increases both anti-HBs IgM and anti-HBs IgG titers and changes the balance of IgG2a and IgG1. Combined use of CnB and CpG induces more cytokines production in splenocytes, as well as more anti-HBs antibodies production in vivo. These results reveal a probable mechanism of CnB-induced inflammatory cytokines production and further demonstrate that CnB is a novel and effective adjuvant of Engerix-B HBV vaccine.

Calcineurin subunit B upregulates β-interferon production by phosphorylation of interferon regulatory factor 3 via Toll-like receptor 4

Toll-like receptors (TLRs) function as pattern-reorganization receptors in mammals and play an essential role in innate immunity. After recognizing certain ligands, TLRs activate a cascade of signal pathways to establish a guard environment. For the first time, we report that in vitro treatment with recombinant calcineurin subunit B (CNB) upregulated several TLR-related genes. Calcineurin subunit B interacted with the ectodomain of TLR4 in vitro. On further investigation, phosphorylation of interferon regulatory factor 3 and degradation of IκB-α were observed by CNB stimulation. In addition to pro-inflammatory cytokines, transcription and production of β-interferon were also enhanced after CNB stimulation. Thus, CNB could be further explored as a cancer and virus immunotherapy drug.

A new function for the calcineurin b subunit: antiplatelet aggregation and anticoagulation

Calcineurin is the only Ca(2+) /calmodulin-dependent serine/threonine protein phosphatase. The roles of the cytosolic calcineurin have been well researched; however, the roles of the serum calcineurin remain unknown. Here, we report that the recombinant human calcineurin B subunit (CnB) can bind to rabbit platelets and show an antiplatelet aggregation activity. Furthermore, CnB exerts an anticoagulant effect by prolonging the activated partial thromboplastin time and thrombin time and reducing the plasma fibrinogen concentration in a dose-dependent manner. We further reveal that the functional domain associated with the anticoagulant activity of CnB is located in the C-terminus. Hemolysis test and intravenous stimulation study show that the recombinant CnB does not cause obvious hemolysis and is safe for intravenous injection. These results reveal a new function of calcineurin B subunit. They also give an explanation for the roles of calcineurin B subunit in serum and point to a possible implication in antithrombotic therapy.

Calcineurin B subunit interacts with proteasome subunit alpha type 7 and represses hypoxia-inducible factor-1α activity via the proteasome pathway

The calcineurin (CN) B subunit (CNB) is the regulatory subunit of CN, which is the only serine/threonine-specific protein phosphatase regulated by Ca2+/CaM. It has been shown to have potential as an anticancer agent, and has a positive effect on the phagocytic index and coefficient. We report here that CNB binds to proteasome subunit alpha type 7 (PSMA7) and inhibits the transactivation activity of hypoxia-inducible factor-1α (HIF-1α) via the proteasome pathway. In addition, we show that CNB represses the expression of vascular endothelial growth factor (VEGF), which is regulated by HIF-1α. These results indicate that CNB modulates cellular proteasome activity via a specific interaction with PSMA7. This may provide a molecular basis for its anticancer and antiviral activities.

Overexpression of calcineurin B subunit (CnB) enhances the oncogenic potential of HEK293 cells

Calcineurin (CaN) is a Ca(2+)/calmodulin (CaM)-stimulated protein phosphatase. It is a heterodimeric enzyme consisting of a catalytic A subunit (CnA) and a Ca(2+)-binding regulatory B subunit (CnB). CaN's key role in vivo is well known, while the function of CnB keeps unclear except that it acts as a regulator of CaN. The present paper shows that CnB overexpression promotes proliferation of human embryonic kidney HEK293 cells by comparing with vector control cells in the complete or serum reduced medium. Furthermore, stable CnB transfectants showed dramatically improved growth in soft agar. And the migration ability of CnB overexpressors also was enhanced remarkably. But in the progress of transformation, the activity of CaN remained unchanged between CnB overexpressors and controls. Therefore, CnB, rather than CaN, is involved in the proliferation promotion of HEK293 cells. Subsequently, 11 proteins with different expression levels between CnB transfectants and controls were identified using two-dimensional gel electrophoresis and electrospray ionization time-of-fight mass spectrometry. Therein, the expression of heat shock protein 27 (HSP27) and protein DJ-1 increased along with CnB overexpression. The important role of CnB in cell neoplastic transformation was found and the possible mechanism was analyzed.

Studies of the anticancer effect of calcineurin B

Calcineurin (CN) is a Ca (2+)/calmodulin-stimulated protein phosphatase. It is a heterodimeric enzyme consisting of a catalytic subunit (CN A) and a Ca2+ -binding regulatory subunit (CN B), which plays an important role in the human immune system. Its regulatory subunit, CN B, on its own, was found to have a remarkable anticancer effect in mice. To clarify the basis of this action the in vivo and in vitro effect of CN B on several types of mice immunocytes was investigated. The phagocytic activity of peritoneal macrophages of both normal mice and mice bearing S 180 solid tumors increased when CN B was injected daily. In vitro examination using a modified MTT assay and an [3H] incorporation assay showed that the cytotoxicity of peritoneal macrophages was increased substantially. CN B also increased the natural killer activity of murine spleen lymphocytes in vivo and in vitro, and synergized with concanavalin A in stimulating their proliferation. Our results indicate that CN B has a significant stimulatory action on the immune system that may partially account for its anticancer activity.