MHC Class I Chain-Related Gene A (MICA) Human Active Protein

This gene encodes the highly polymorphic major histocompatability complex class I chain-related protein A. The protein product is expressed on the cell surface, although unlike canonical class I molecules it does not seem to associate with beta-2-microglobulin. It is a ligand for the NKG2-D type II integral membrane protein receptor. The protein functions as a stress-induced antigen that is broadly recognized by intestinal epithelial gamma delta T cells. Variations in this gene have been associated with susceptibility to psoriasis 1 and psoriatic arthritis, and the shedding of MICA-related antibodies and ligands is involved in the progression from monoclonal gammopathy of undetermined significance to multiple myeloma. Alternative splicing of this gene results in multiple transcript variants. [provided by RefSeq, Jan 2014]

MICA: Seems to have no role in antigen presentation. Acts as a stress-induced self-antigen that is recognized by gamma delta T- cells. Ligand for the KLRK1/NKG2D receptor. Binding to KLRK1 leads to cell lysis. Anti-MICA antibodies and ligand shedding are involved in the progression of monoclonal gammopathy of undetermined significance (MGUS)to multiple myeloma. Genetic variations in MICA may be a cause of susceptibility to psoriasis type 1 (PSORS1). Psoriasis is a common, chronic inflammatory disease of the skin with multifactorial etiology. It is characterized by red, scaly plaques usually found on the scalp, elbows and knees. These lesions are caused by abnormal keratinocyte proliferation and infiltration of inflammatory cells into the dermis and epidermis. Genetic variation in MICA is a cause of susceptibility to psoriatic arthritis (PSORAS). PSORAS is an inflammatory, seronegative arthritis associated with psoriasis. It is a heterogeneous disorder ranging from a mild, non-destructive disease to a severe, progressive, erosive arthropathy. Five types of psoriatic arthritis have been defined: asymmetrical oligoarthritis characterized by primary involvement of the small joints of the fingers or toes; asymmetrical arthritis which involves the joints of the extremities; symmetrical polyarthritis characterized by a rheumatoidlike pattern that can involve hands, wrists, ankles, and feet; arthritis mutilans, which is a rare but deforming and destructive condition; arthritis of the sacroiliac joints and spine (psoriatic spondylitis). Belongs to the MHC class I family. MIC subfamily. 2 isoforms of the human protein are produced by alternative splicing.

Protein type: Membrane protein, integral

Chromosomal Location of Human Ortholog: 6p21.33

Cellular Component: extracellular space; cell surface; integral to plasma membrane; cytoplasm

Molecular Function: protein binding; beta-2-microglobulin binding; antigen binding; natural killer cell lectin-like receptor binding

Biological Process: antigen processing and presentation; viral reproduction; natural killer cell mediated cytotoxicity; response to heat; cytolysis; defense response to bacterium; immune response to tumor cell; gamma-delta T cell activation; defense response to virus; response to DNA damage stimulus; T cell mediated cytotoxicity

Disease: Psoriatic Arthritis, Susceptibility To; Psoriasis 1, Susceptibility To