Stressed out: NKp46 binds ecto-calreticulin

Area of Science:

• Immunology
• Cell Biology
• Molecular Medicine

Background:

• Natural killer (NK) cells are crucial for innate immunity, identifying and eliminating stressed, infected, or malignant cells.
• Calreticulin (CRT) is a protein typically found within the endoplasmic reticulum.
• Externalized calreticulin (ecto-CRT) has been observed on stressed cells, but its specific role in NK cell recognition was unclear.

Purpose of the Study:

• To investigate the interaction between the NK cell receptor NKp46 and externalized calreticulin (ecto-CRT).
• To elucidate the mechanism by which ecto-CRT signals NK cells to eliminate target cells.

Main Methods:

• Utilized co-immunoprecipitation and flow cytometry to assess NKp46-ecto-CRT binding.
• Employing cellular assays to measure NK cell degranulation and target cell lysis upon NKp46 engagement.
• Inducing endoplasmic reticulum stress in target cells to promote ecto-CRT exposure.

Main Results:

• Demonstrated direct binding of the activating NK cell receptor NKp46 to ecto-CRT.
• Showed that NKp46-ecto-CRT interaction leads to NK cell degranulation and subsequent target cell killing.
• Confirmed that endoplasmic reticulum stress-induced ecto-CRT functions as a danger-associated molecular pattern.

Conclusions:

• The NKp46 receptor recognizes ecto-CRT as a signal of cellular distress.
• This recognition pathway facilitates NK cell-mediated elimination of compromised cells, including those that are infected, malignant, stressed, or senescent.
• Highlights a novel mechanism for NK cell-mediated immunity involving ecto-CRT as a key molecular target.