Germline PTEN Promoter Mutations and Deletions in Cowden/Bannayan-Riley-Ruvalcaba Syndrome Result in Aberrant PTEN Protein and Dysregulation of the Phosphoinositol-3-Kinase/Akt Pathway

Abstract

Germline intragenic mutations in PTEN are associated with 80% of patients with Cowden syndrome (CS) and 60% of patients with Bannayan-Riley-Ruvalcaba syndrome (BRRS). The underlying genetic causes remain to be determined in a considerable proportion of classic CS and BRRS without a polymerase chain reaction (PCR)-detectable PTEN mutation. We hypothesized that gross gene deletions and mutations in the PTEN promoter might alternatively account for a subset of apparently mutation-negative patients with CS and BRRS. Using real time and multiplex PCR techniques, we identified three germline hemizygous PTEN deletions in 122 apparently mutation-negative patients with classic CS (N=95) or BRRS (N=27). Fine mapping suggested that one deletion encompassed the whole gene and the other two included exon 1 and encompassed exons 1-5 of PTEN, respectively. Two patients with the deletion were diagnosed with BRRS, and one patient with the deletion was diagnosed with BRRS/CS overlap (features of both). Thus 3 (11%) of 27 patients with BRRS or BRRS/CS-overlap had PTEN deletions. Analysis of the PTEN promoter revealed nine cases (7.4%) harboring heterozygous germline mutations. All nine had classic CS, representing almost 10% of all subjects with CS. Eight had breast cancers and/or benign breast tumors but, otherwise, oligo-organ involvement. PTEN protein analysis, from one deletion-positive and five PTEN-promoter-mutation-positive samples, revealed a 50% reduction in protein and multiple bands of immunoreactive protein, respectively. In contrast, control samples showed only the expected band. Further, an elevated level of phosphorylated Akt was detected in the five promoter-mutation-positive samples, compared with controls, indicating an absence of or marked reduction in functional PTEN. These data suggest that patients with BRRS and CS without PCR-detected intragenic PTEN mutations be offered clinical deletion analysis and promoter-mutation analysis, respectively.

Novel and recurrent mutations in theNF1 gene in Italian patients with neurofibromatosis type 1

“…In this respect, sequencing by hybridization (SbH), a technique which involves hybridization of the DNA of unknown sequence with an enormous set of short oligonucleotides seems particoularly promising (Drmanac et al, 2002). In addition, real time and multiplex PCR technique (Zhou et al, 2003), a method designed for the detection of multi-exon deletions, should also be considered in order to assess the role of this type of mutations as cause of NF1.…”

Nuclear localization signals and human disease

“…Although no NLS has been defined in PTEN, it is also found in the nucleus in various cell lines and tissues (106). Recently, amino acid substitutions at two lysine residues (K13 and K289) within PTEN have been linked to Cowden syndrome (107), an autosomal dominant disease that leads to high susceptibility to various cancers (108). Although these PTEN mutants retain catalytic activity, PTEN is excluded from the nucleus in Cowden syndrome patient tissues (107).…”

Increased PTEN expression due to transcriptional activation of PPARγ by Lovastatin and Rosiglitazone

“…1 Germline mutations in PTEN (protein phosphatase and tensin homolog located on chromosome ten), a tumor suppressor gene, are associated with 85% of patients with the autosomal dominant disorder Cowden syndrome (CS). [2][3][4] Patients with CS have a 25-50% risk of developing breast cancer. 5,6 CS patients have also been reported to have mucocutaneous lesions, thyroid abnormalities, fibrocystic disease, uterine leiomyoma and macrocephaly.…”

“…7,8 Germline PTEN mutations are also associated with 65% of patients with Bannayan-Riley-Ravalcaba Syndrome, which is characterized by macrocephaly, lipomatosis, hemangiomatosis and speckled penis. 4,9 Somatic alterations in PTEN, whether by genetic or epigenetic mechanisms, play some role in the pathogenesis of a broad range of solid tumors, such as carcinomas of the breast, thyroid, endometrium and colon. 10 PTEN's protein product, PTEN, is a dual specificity phosphatase with both lipid and protein phosphatase activity.…”