CADM1 is expressed as multiple alternatively spliced functional and dysfunctional isoforms in human mast cells

Elena P Moiseeva,Mark L Leyland,Peter Bradding

doi:10.1016/j.molimm.2012.08.024

Elena P Moiseeva, Mark L Leyland + Show 1 more

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https://doi.org/10.1016/j.molimm.2012.08.024

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Journal: Molecular immunology	Publication Date: Oct 10, 2012
Citations: 17	License type: cc-by

Affiliation: University of Leicester

Abstract

Cell adhesion molecule 1 (CADM1) is implicated in the pathogenesis of several diseases and is responsible for adhesion and survival of mast cells (MCs). Differential expression of CADM1 isoforms was found in different species. We previously cloned SP4, SP1, SP6 and a dysfunctional isoform from human lung MCs (HLMCs) and the MC line HMC-1. The aim of this study was to identify all isoforms expressed in human MCs. The functional isoforms SP4, SP1, SP6 and SP3, with alternative splicing between exons 7/11, were detected in human MCs by RT-PCR. Two dysfunctional isoforms with alternative splicing of cryptic exons A and B between exons 1/2, leading to premature termination of translation, were found in ∼40% of MC specimens. Sequencing of genomic DNA showed that splicing of cryptic exon B did not result from specific SNPs within this exon or its putative splice branch point. Highly glycosylated CADM1 (∼105kDa) was detected by western blotting, but an extracellular domain (∼95kDa) was found only in the culture medium from HLMCs, but not HMC-1 cells, indicating differential protein expression. Transfection of SP1 and SP6, but not SP4, reduced adhesion of HMC-1 cells to human lung fibroblasts but not airway smooth muscle cells. Hence, dysfunctional and functional CADM1 isoforms are found in human MCs. The longer SP1 and SP6 were most evident in differentiated HLMCs and displayed differential adhesion compared to SP4. These multiple isoforms are likely to contribute to MC function in both health and disease.

Highlights

The Cell adhesion molecule 1 (CADM1) gene encodes a cell adhesion receptor CADM1, which belongs to an immunoglobulin family of ten genes, which include CADM2-4, PVRL1-4, PVR, and CRTAM, according to Ensembl (Flicek et al, 2011)
We investigated whether the SP5 isoform was present in human mast cells (MCs)
The failure to detect SP5 in human MCs is important as it has been cloned from mouse MCs, where it is proposed to function as a negative regulator of CADM1 function (Koma et al, 2004)

Summary

Introduction

The CADM1 (cell adhesion molecule 1) gene encodes a cell adhesion receptor CADM1 ( known as IGSF4, TSLC1, Necl-2, SynCAM1), which belongs to an immunoglobulin family of ten genes, which include CADM2-4, PVRL1-4, PVR, and CRTAM, according to Ensembl (Flicek et al, 2011). Human CADM1 was originally identified as a tumour suppressor of lung cancer 1 (TSLC1; SP4) (Kuramochi et al, 2001). It is essential for human health, since modulation of expression, SNPs or mutations in CADM1 have been implicated in several diseases including cancer, autism spectrum disorder and venous thrombosis (Gomyo et al, 1999; Hasstedt et al, 2009; Zhiling et al, 2008). All identified counter-receptors for CADM1 belong to the same family They include CADM1 itself, CADM2, CADM3, nectin and CRTAM (Fogel et al, 2007; Galibert et al, 2005; Masuda et al, 2002; Shingai et al, 2003). CD155 binding to CADM1 is controversial (Shingai et al, 2003; Wakayama et al, 2007)

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