Background: Hyperparathyroidism affects most patients with multiple endocrine neoplasia type 1 (MEN 1). This study investigates expression of the candidate MEN1 gene phospholipase C beta 3 (PLC beta 3) and expression and function of a putative calcium sensing protein (CAS) in hyperparathyroidism of MEN 1.
Methods: In 31 parathyroid glands from 17 patients with MEN 1, CAS distribution was studied immunohistochemically and parallel sections were explored for PLC beta 3 mRNA expression by in situ hybridization. Enzymatically dispersed parathyroid cells were analyzed for cytoplasmic calcium concentrations [Ca2+]i and parathyroid hormone (PTH) release.
Results: All glands exhibited a heterogeneously reduced CAS immunoreactivity, especially meager in nodularly assembled parathyroid cells. Calcium regulated [Ca2+]i and PTH release tended to be more deranged in the glands possessing the lowest immunostaining. Parathyroid PLC beta 3 invariably was homogeneously expressed, and this included even MEN 1 patients with reduced PLC beta 3 expression in endocrine pancreatic tumors.
Conclusions: The findings support variable calcium insensitivity of [Ca2+]i and PTH release in hyperparathyroidism of MEN 1, apparently coupled to heterogeneously reduced CAS expression. For clarification of the role of PLC beta 3 in MEN 1 parathyroid tumorigenesis further study of this protein is required.