Identification of germline mutation of PTEN gene and analysis of apoptosis resistance of the lymphocytes in a patient with Cowden disease

Abstract

Mutations of the tumor suppressor gene PTEN have been reported in patients with Cowden disease (CD) and in several malignant tumors. We analyzed a germline mutation of the PTEN gene in a patient with CD and identified a 4-bp deletion in exon 8 of the PTEN gene. The same germline mutation was detected in 3 members of her family. The mutated gene was predicted to encode a C-terminal truncated PTEN protein. Immunoblotting analysis revealed that the expression level of the wild-type PTEN protein in the patient's lymphocytes was reduced to almost half the level of the control lymphocytes, and the predicted truncated mutant PTEN could not be detected. Since PTEN is known to function as a negative regulator of the phosphatidylinositol-3-kinase signal pathway that promotes cell survival, the patient's lymphocytes were tested for the resistance against the apoptotic stimulus. It was shown that the patient's lymphocytes were more resistant to apoptosis induced by calcium ionophore than the healthy control lymphocytes. These results indicate that the germline mutation of the PTEN gene and the consequent loss of heterozygous expression may lead to an increase in the survival potential of cells, thereby elucidating a role of PTEN in the pathogenesis of tumor generation and hyperplasia of lymphoid tissue in CD.