CD99 isoforms regulate CD1a expression in human monocyte‐derived DCs through ATF‐2/CREB‐1 phosphorylation

Abstract

CD1a expression is considered one of the major characteristics qualifying in vitro human dendritic cells (DCs) during their generation process. Here, we report that CD1A transcription is regulated by a mechanism involving the long and short isoforms of CD99. Using a lentiviral construct encoding for a CD99 short hairpin RNA, we were able to inhibit CD99 expression in human primary DCs. In such cells, CD1a membrane expression increased and CD1A transcripts were much higher in abundance compared to cells expressing CD99 long form (CD99LF). We also show that CD1A transcription is accompanied by a switch in expression from CD99LF to expression at comparable levels of both CD99 isoforms during immature DCs generation in vitro. We demonstrate that CD99LF maintains a lower level of CD1A transcription by up-regulating the phosphorylated form of the ATF-2 transcription factor and that CD99 short form (SF) is required to counteract this regulatory mechanism. Elucidation of the molecular mechanisms related to CD99 alternative splicing will be very helpful to better understand the transcriptional regulatory mechanism of CD1a molecules during DCs differentiation and its involvement in the immune response.Keywords: alternative splicing-ATF2-CREB1 r CD99 r Dendritic cells r Nonclassical MHC Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionPresentation of foreign antigens in the form of proteins or lipids solicits specialized molecular complexes carried by dendritic cells (DCs). The molecules of the classical and nonclassical major Correspondence: Dr. Ghislaine Bernard e-mail: bernardg@unice.fr histocompatibility complex (MHC) class I present antigens to T cells and these two families of molecules have very similar structures [1][2][3].Among the nonclassical MHC molecules is the CD1 family of molecules that assures the presentation of lipid and glycolipid † Deceased C 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2016. 46: 1460-1471 Immunomodulation 1461 antigens [4,5]. This family consists of five genes, including CD1A, B, C, D and E. The first four give rise to cell surface proteins CD1a, CD1b, CD1c, CD1d that are able to present the antigens, while the gene CD1E codes for the cytoplasmic protein CD1e [6][7][8]. CD1a is expressed on the membranes of thymocytes, dermal DCs and Langerhans cells, and allows distinction between subpopulations of DCs. No such equivalent has been reported in mice [8].CD1a is expressed during generation of DCs derived from monocytes when cultured in the presence of GMCSF and IL4 in vitro [9]. Two subpopulations of immature DCs (iDCs), i.e. CD1a high and CD1a low DCs, are produced in these conditions [10,11]. In addition to their phenotypic differences, these cells show functional differences, in particular in terms of secretion of cytokines. In contrast to CD1a high DCs, CD1a low DCs produce low amounts of IL12 but produce high amounts of IL10. This profile of cytokines impacts on the f...

CD99: A Cell Surface Protein with an Oncojanus Role in Tumors

“…Single-positive thymocytes and peripheral T cells display an exclusive expression of the full-length CD99wt isoform, whereas double-positive thymocytes and some immature T cell lines express both isoforms [ 20 ], indicating a tight correlation with T cell differentiation. In addition, the expression of the CD99 isoforms correlates with that of CD1a in human thymocytes; double-positive thymocytes express CD1a and the two forms of CD99, while single-positive thymocytes that have lost the expression of CD1a express only the long form of CD99 [ 31 ]. Among B cells, B cell precursors with acute lymphoblastic leukemia (BCPs-ALL) express mainly the long form of CD99, while in normal B cell precursors (BCPs), CD99 is downregulated during differentiation.…”

“…CD99 has been found to participate in various steps of T and B cell development and differentiation [ 30 , 34 , 35 ] and it regulates crucial functions, such as the proliferation and activation of T lymphocytes [ 36 , 37 ], apoptosis [ 30 , 38 ], adhesion [ 19 , 34 , 39 , 40 ], lymphocytes diapedesis to the inflamed vascular endothelium [ 41 , 42 ], and intracellular membrane protein trafficking [ 43 , 44 , 45 , 46 ]. In particular, CD99 plays an active role in the transport and expression of major histocompatibility complex (MHC) class I and II and in TCR expression on thymocytes [ 43 , 44 , 45 ] and in the regulation of CD1a expression on dendritic cells [ 31 ]: thus, CD99 is a critical determinant in the orientation of the immune response.…”

“…This finding further supports the need for additional studies to elucidate the relationship between the two isoforms and their effect on cellular signaling. CD99 isoforms have also been found to have counteracting effects on the regulation of the expression of CD1, a non-classical MHC molecules that ensures the presentation of lipid and glycolipid antigens, during dendritic cells differentiation [ 31 ], whereas MHC class I and II are associated with both CD99 isoforms [ 54 ].…”

Escape from X chromosome inactivation and female bias of autoimmune diseases

“…Cernadas et al identified a regulatory role for CD99 in the expression of cluster of differentiation 1a (CD1a) in which isoform variants of CD99 possess opposing effects on the CD1a expression in human monocytederived DCs. While CD99 long-form decreased CD1a transcription, the short-form of CD99 counteracted this effect (Mahiddine 2016). Basically, CD1a molecules which are structurally similar to MHC I, are known for their functions in the presentation of lipid and glycolipid antigens to gamma delta T cells.…”

CD99 at the crossroads of physiology and pathology

“…In addition, the cytoplasmic regions of the two CD99 isoforms contain shared motifs such as a zone rich in positively charged amino acids and a cysteine residue. An SHR motif for PKC and a leucine repeat are present only in the long form of CD99 (Mahiddine et al 2016 ). It has been demonstrated that the cytoplasmic domain of the long form contains two putative phosphorylation sites, a serine at amino acid residue 168 (S168) and a threonine at amino acid residue 181 (T181).…”