ZSWIM1: A novel biomarker in T helper cell differentiation

Highlights

• ZSWIM1, a SWIM domain protein, is expressed in lymphocytes and particularly enriched in naïve CD4+ T cells.

• ZSWIM1 is selectively expressed in Th17 cells compared to Th1 cells.

• ZSWIM1 expression was maintained in cells polarised under Th17 cytokine conditions, but reduced in Th1 polarised cells.

• Activation sensitive expression of ZSWIM1 implies it may have a novel function in T helper cells.

Abstract

The effector memory CD4+ Th17 cells play critical roles in bacterial immunity and pathological inflammation in autoimmune conditions. ZSWIM1 is a gene encoding a protein of unknown function in leukocytes—but containing a zinc finger SWIM motif. In peripheral blood mononuclear cells, the expression of ZSWIM1 is highest in lymphocytes, and in particular shows greatest abundance in naive CD4+ T cells. Upon polarisation of naïve CD4+ T cells, ZSWIM1 expression is retained in Th17 cells but is selectively down regulated in Th1 cells. Similarly in in vitro expanded effector memory CD4+ T cells, ZSWIM1 was more abundant in Th17 cells compared to Th1 or Th17 polyfunctional (Th17pf) cells, which produce IL-17A and IFNγ. Although stimulation of cytokine production by PMA and ionomycin reduced ZSWIM1 expression, the relative differences in abundance between the cell types were maintained. The activation sensitive nature of ZSWIM1 expression suggests that it may play a novel role in the development or function of T helper cells.

Introduction

Understanding the roles of different leukocyte lineages and in particular functional subsets of T cells in normal and pathological immunity has been the cornerstone of modern immunology. The study of functional cell subsets has depended heavily on the identification of cell surface or intracellular molecules that have a restricted or ideally, exclusive expression on particular cell types. The investigation of functional characteristics including surface markers, cytokine production and nuclear factors, has led to the identification of a number of T helper cells including: Th1 and Th2 cells which are the major players in response against bacterial and viral foreign pathogens [1], [2], [3], Th17 cells which mediate inflammation [4], [5], [6], as well as T regulatory cells [7], [8], T follicular helper cells [9], and suggested classifications for Th22 [10], [11] and Th9 [12], [13] cells.

While playing an essential role in normal immunity, Th17 cells have also been implicated in the development of human autoimmune diseases [14], [15], [16], [17]. The Th17 cell is well defined as producing the cytokine IL-17A, but it is also capable of secreting many other cytokines such as IL-17F, CCL20, GM-CSF, and IL-6 in an inflammatory response [18], [19]. Surface markers that are commonly used to identify Th17 cells include CCR6, CCR4 and CD161 [20], [21], [22]. In addition to surface markers, intracellular molecules such as cytoplasmic IL-17A and the transcription factor RORγt (encoded by RORC) that promotes IL-17A transcription are particularly useful markers of Th17 cells [22], [23], [24].

Considerable efforts are being made to identify novel molecules associated with the development and function of leukocyte subsets. Various systems biology approaches [21], [25] have identified many genes and proteins of little or no known functional characterisation including the ZSWIM family of proteins.

The zinc finger, SWIM-type containing 1 gene, or ZSWIM1 is located on chromosome 20 of the human genome. It has a transcript length of 2787 bp. There is one identified synonymous single-nucleotide polymorphism (SNP) at position 905, annotated in the ENTREZ SNP data base [26]. The gene encodes a protein of 485 amino acids which is predicted to only contain one functional domain. The SWIM domain derives its name from the SWI2/SNF2 family of ATPases and MuDr plant transposases, as the newly identified domain was found to have the closest alignments to these two protein families in both prokaryotes and eukaryotes [27]. The SWIM domain is defined by the motif sequence CxCx_nCxH, where n = 5–39 amino acids [27]. The cysteine and histidine residues imply this domain is likely to adopt a zinc finger-like structure [28], [29].

While the specific function of the ZSWIM1 is unknown, the presence of a zinc finger-like structure taken together with the observation that other proteins containing SWIM domains interact with other macromolecules suggests that ZSWIM1 may mediate its function by protein-protein interactions or DNA binding capabilities [30], [31].

In this study we define the expression of human ZSWIM1 in leukocytes and demonstrate the differential modulation of ZSWIM1 expression during Th polarisation. We analysed the expression in in vitro expanded Th17 cells, Th1 cells and Th17 polyfunctional cells (co-producer of IL-17A and IFNγ).