Gene Section Review Atlas Genet Cytogenet Oncol Haematol. 2015; 19(5) 340 Atlas of Genetics and Cytogenetics in Oncology and Haematology INIST-CNRS OPEN ACCESS JOURNAL MICA (MHC class I polypeptide-related sequence A) Zain Ahmed, Medhat Askar Cleveland Clinic/, Cleveland, OH; askarm@ccf.org Published in Atlas Database: July 2014 Online updated version : http://AtlasGeneticsOncology.org/Genes/MICAID41364ch6p21.html Printable original version : http://documents.irevues.inist.fr/bitstream/handle/2042/62122/07-2014-MICAID41364ch6p21.pdf DOI: 10.4267/2042/62122 This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 2.0 France Licence. © 2015 Atlas of Genetics and Cytogenetics in Oncology and Haematology Abstract Human Major Histocompatibility Complex (MHC) Class I Chain-Related gene A (MICA) is located 46 Kb centromeric to the HLA-B locus on the short arm of human chromosome 6 and encodes for a 62- kda cell surface glycoprotein. It is expressed on endothelial cells, dendritic cells, fibroblasts, epithelial cells, and many tumours and serves as target for both cellular and humoral immune responses in transformed cells. MICA protein at normal states has a low level of expression in epithelial tissues but is upregulated in response to various stimuli of cellular stress. MICA also functions as a ligand recognized by the activating receptor NKG2D that is expressed on the surface of NK, NKT, CD8+ and TCRγδ+ T cells. Allelic variants of MICA due to a single amino acid substitution at position 129 in the α2 domain have been reported to result in large differences in NKG2D binding. These variable affinities have been suggested to affect thresholds of NK cell triggering and T cell modulation in autoimmune diseases and malignancies. MICA molecules exist also in soluble forms (sMICA) and altered serum levels of sMICA have been reported in multiple states of health and disease. Keywords MICA, MHC, Malignancy, Autoimmunity, NK cells; Transplantation; Rejection; GVHD Identity Other names MHC (Human Major Histocompatibility Complex) Class I Chain-Related Gene A, MHC Class I Chain-related Protein A, MHC class I-related chain A, MIC-A, PERB11.1 HGNC (Hugo): MICA Location: 6p21.33 Figure 1: Chromosomal location of MICA genes shown on a map of the MHC on chromosome 6p21.3 (not to scale). Chromosome 6 [Drawing modified from the National Library of Medicine, the National Center for Biotechnology Information public website (2013)]