Immunohistochemical assessment of parafibromin in mouse and human tissues

Parafibromin is a protein encoded by the HRPT2 oncosuppressor gene, whose mutation causes the hyperparathyroidism–jaw tumour syndrome, characterized by the occurrence of parathyroid adenoma or carcinoma, fibro‐osseous jaw tumours, and renal neoplastic and non‐neoplastic abnormalities. Non‐morphological techniques, such as Northern and Western blotting and reverse transcriptase‐PCR, indicate that parafibromin is ubiquitously expressed, but extensive immunohistochemical studies have not been performed. To increase our knowledge of the distribution and patterns of expression of parafibromin, we examined its expression and location in many different mouse and human organs by immunohistochemistry. There were no substantial differences in parafibromin expression between mouse and human. We found widespread expression of parafibromin, except in connective tissue, smooth muscle, endothelium and some other types of epithelia (colonic, urinary, tubaric, uterine, thyroid). Heterogeneity of positivity intensity and subcellular location (nuclear, nucleocytoplasmic, cytoplasmic) was found between tissues and cell types, suggesting differential functional involvement of parafibromin. Moreover, higher parafibromin expression was found in cell types, such as hepatocytes, cells of the base of gastric glands, renal cortex tubules and the pars intermedia of the hypophysis, which are characterized by different proliferative capacity, thus indicating that the cellular function of parafibromin may not be reduced only to its anti‐proliferative effect.