Nitric-oxide Synthase 2 Interacts with CD74 and Inhibits Its Cleavage by Caspase during Dendritic Cell Development

Abstract

Dendritic cells (DC) are professional antigen-presenting cells that possess specific and efficient mechanisms to initiate immune responses. Upon encounter with pathogens, immature DC will go through a maturation process that converts them to highly immunogenic mature DC. Despite the fact that nitric oxide (NO) was produced in large amounts in maturing DC, it is still unclear whether NO is the key molecule that initiates and enhances DC maturation and T cell proliferation, respectively. Here, we report that NO donor and overexpression of either nitric-oxide synthase 2 (NOS2) or nitric-oxide synthase 3 (NOS3) alone can induce surface expression of major histocompatibility complex class II (MHC II) and both the essential co-stimulatory molecules CD80 and CD86 in immature DC. Consistently, NO donor-treated immature DC were capable of enhancing T cell proliferation in vitro in the absence of lipolysaccharide. Interestingly, NOS2 interacts with CD74 (the MHC II-associated invariant chain), and the degradation of CD74 by caspases in immature DC was inhibited upon treatment with NO donor. Because the trafficking of MHC II is CD74-dependent, the increase in cell surface localization of MHC II in maturing DC is in part due to the increase in CD74 protein expression in the presence of NOS2 and NO. Dendritic cells (DC)2 are professional antigen-presenting cells that possess specific and efficient mechanisms to initiate immune responses. Major histocompatibility complex class II (MHC II) molecules bind peptides derived from internalized proteins that have entered the endocytic pathway and present them at the cell surface for the activation of CD4 ϩ T cells. Upon encounter with pathogens, immature DC go through a maturation process that converts them to highly immunogenic mature DC. Immature DC are good at capturing pathogens or foreign antigens, but most of the intracellular MHC II molecules that can bind and present antigens to T cells are localized to the late endosomes. In mature DC, MHC II molecules are free to traffic to the cell surface together with their peptides to present to T cells. Some protein molecules play essential roles in controlling the retention and trafficking of MHC II in DC. We previously showed that in the immature DC, a number of endosomal proteins were degraded by caspases (1, 2). However, in maturing DC, protein degradation by caspases was inhibited, presumably by NO (1). NO is a central messenger molecule in vascular regulation, immunity, and neurotransmission (3, 4). Despite the fact that NO was produced in large amounts in lipopolysaccharide (LPS)-treated DC, it is still unclear whether NO alone can contribute directly to the initiation and induction of DC maturation and T cell proliferation, respectively, in the absence of LPS.Here, we report that NO donor-treated immature DC were capable of enhancing T cell proliferation in vitro in the absence of LPS. In addition, the MHC II-associated invariant chain (CD74) was up-regulated in immature DC upon treatment with NO donor. CD74 is a type II integ...

A novel CARD containing splice-isoform of CIITA regulates nitric oxide synthesis in dendritic cells

“…NO then further inhibits caspases and enhances NOS2 expression and NO synthesis in mature DC. We have shown previously that inhibition of caspases by NO upregulates expression of CD74 (Huang et al, 2008) and other endosomal proteins (Wong et al, 2004;Santambrogio et al, 2005), which is essential for regulating the MHC IIrestricted antigen presentation pathway. This subsequently enhances the capability of DC in inducing T cell proliferation/ activation.…”

“…Other than induction of MHC genes by DC-CIITA, NO synthesis is also (Huang et al, 2008) essential for DC maturation. Consistently, our study shows that a novel DC-CIITA splicing isoform, DC-CASPIC, regulates the expression of NOS2 and NO synthesis in the maturing DC.…”

“…We have previously shown that NO is the key molecule that regulates the expression of cell surface MHC II and the antigen presentation in DC (Huang et al, 2008). Since DC-CASPIC is upregulated during DC maturation and it can induce NOS2 expression and NO synthesis, we hypothesized that DC-CASPIC also has important roles in DC functions.…”

“…8A, CI-treatment upregulated the protein level of NOS2, thus indicating that NOS2 is a substrate for caspases. NO-donor (NONOate), which inhibits caspases-induced protein degradation, was utilized as positive control (Kim et al, 2002;Brüne, 2003;Huang et al, 2008).…”

Atividade imunomoduladora do óxido nítrico na resposta <i>in vitro</i> de células mononucleares de recém-natos e adultos.

“…A iNOS metaboliza esse aminoácido em citrulina e NO, enquanto a arginase em ornitina e ureia (adaptado de BOGDAN, 2011). (HUANG et al, 2008). Em humanos, entretanto, apesar de resultados bastante controversos, há evidências de que há um aumento de expressão de outra isoforma, nNOS, que também é importante para um aumento de expressão de moléculas coestimuladoras como CD80 e CD83, e secreção de citocinas como IL-12p40, IFN-γ, IL-4 e IL-13 (ADLER et al, 2010).…”