Calretinin

Calretinin also known as 29 kDa calbindin is a is_associated_with::vitamin D-dependent calcium-binding protein involved in is_associated_with::calcium signaling. In humans, the calretinin protein is encoded by the CALB2 is_associated_with::gene.

Function
This gene encodes an intracellular calcium-binding protein belonging to the is_associated_with::troponin C superfamily. Members of this protein family have six EF-hand domains which bind calcium. This protein plays a role in diverse cellular functions, including message targeting and intracellular calcium buffering. It also functions as a modulator of neuronal excitability

Calretinin is abundantly expressed in neurons and in hair follicles.

Clinical significance
Calretinin is a diagnostic marker for some human diseases, including is_associated_with::Hirschsprung disease and some cancers.

Mesothelioma
Using is_associated_with::immunohistochemistry, calretinin can be demonstrated in both benign is_associated_with::mesothelium and in malignant is_associated_with::mesothelioma and can be used to help differentiate different lung tumours. Antibodies to calretinin can also be used to distinguish between different types of is_associated_with::brain tumour, demonstrating only those with is_associated_with::neuronal rather than glial, differentiation.

Hirschsprung disease
In is_associated_with::Hirschsprung disease, calretinin IHC offers additional diagnostic value in specimens with inadequate amount of is_associated_with::submucosa and rarely seen is_associated_with::ganglion cells. The presence of ganglion cells consistently correlated with calretinin-positive thin nerve fibrils in the is_associated_with::lamina propria, is_associated_with::muscularis mucosae and superficial submucosa. These calretinin-positive thin is_associated_with::nerve fibrils are absent in the aganglionic segments of is_associated_with::bowel and in the areas without ganglion cells from the junction of normal with diseased is_associated_with::rectum. Calretinin is strongly expressed in the submucosal and is_associated_with::subserosal is_associated_with::nerve trunks in the ganglionic segment. No calretinin expression is seen in the nerve trunks in the rest of the aganglionic segment. It has faint expression in the thick nerve trunks from the areas without ganglion cells. Faint positivity of the thick submucosal and subserosal nerves in the absence of ganglion cells and calretinin positive nerve fibrils, is characteristic of the junction of the aganglionic-to-normal rectum.