# Calreticulin-Mediated Quality Control of the Non-Classical MHC-I Molecule MICA: Implications for Immune Surveillance

## TL;DR

This study explores how the protein calreticulin helps regulate MICA, a key immune molecule, and how this process might be disrupted in melanoma to avoid immune detection.

## Contribution

The study identifies calreticulin as a regulator of MICA maturation and suggests its role in immune evasion in melanoma.

## Key findings

- MICA is retained intracellularly and colocalizes with calreticulin in melanoma cells and healthy skin.
- Calreticulin preferentially interacts with a low-molecular-weight, non-glycosylated form of MICA.
- CRT-dependent retention of MICA may act as a physiological checkpoint disrupted in melanoma.

## Abstract

Major histocompatibility complex class I chain-related gene A (MICA) is a non-classical MHC-I molecule essential for immune surveillance, yet its intracellular maturation remains poorly understood. We show that MICA is predominantly retained intracellularly in melanoma cells and colocalizes with the endoplasmic reticulum chaperone calreticulin (CRT). Notably, MICA also colocalizes with CRT in healthy skin. Immunoprecipitation assays reveal that CRT preferentially associates with a low-molecular-weight form of MICA. Recombinant protein assays and in silico analyses support direct interaction between CRT and non-glycosylated MICA, but not with fully glycosylated eukaryotic MICA. These findings identify CRT-dependent retention of MICA as a physiological checkpoint that may be dysregulated in melanoma to promote immune evasion.