Mutations in the PTEN tumor gene and risk of endometriosis: a case-control study

Are mutations in the phosphatase and tensin homolog deleted on chromosome 10 (PTEN) gene associated with endometriosis?

Loss of heterozygosity (LOH) at the 10q23.3 locus, PTEN somatic mutations and changes in the levels and distribution of proteins in the PTEN-PI3K/Akt signal transduction pathway are associated with endometriosis.

Endometriosis has a strong genetic basis. Recent genome-wide association and linkage studies have reported a significant association of endometriosis with 7p15.2, 9p21 and 10q23-26 loci. PTEN, which maps to 10q23.3, acts as a tumor suppressor gene through the action of its phosphatase protein product, phosphatase and tensin homolog (PTEN). This phosphatase is involved in the regulation of the cell cycle, and mutations of PTEN are a step in the development of many cancers.

A total of 1252 subjects of Indian origin (endometriosis patients = 752; controls = 500) were recruited to participate in this case-control study. Recruitment took place from 2001 to 2009 at Institute of Reproductive Medicine (IRM), Kolkata, India; Infertility Institute and Research Centre (IIRC), Secundrabad, India and Vasavi Medical and Research Centre, Hyderabad, India.

LOH on 10q, 9p and 7p was analyzed in analogous ectopic-eutopic endometria along with blood samples from 32 advanced stage endometriosis patients by PCR-GeneScan analysis. Genotyping of PTEN was carried out on genomic DNA of analogous ectopic-eutopic endometria (n = 32) as well as blood samples from 720 patients and 500 controls by PCR-sequencing analysis to explore somatic and germ-line mutations, respectively. The levels and distribution of PTEN, p-Akt, p-Bad and p27 were analyzed in the eutopic endometria of patients (n = 5) and controls (n = 5) using western-blot and immunohistochemistry.

PCR-GeneScan analysis revealed a higher LOH frequency at 10q23.3 (84.4%) compared with other loci analyzed, hence we focused our attention on PTEN. PCR-sequencing analysis revealed seven novel somatic mutations and 23 germ-line polymorphisms in patients. Among somatic mutations, a frame-shift insertion at 10:89692992-89692993 (in the functionally important N-terminal phosphatase domain of PTEN) occurred in 11 of the 32 ectopic endometria. Western-blot and immunohistochemical analysis revealed decreased PTEN and increased p-Akt and p-Bad levels in eutopic endometria of patients compared with controls (all comparisons, P < 0.0001). Furthermore, PTEN loss was more frequent in the nucleus than in the cytoplasm. Expression of p27 did not differ between patients and controls.

Protein analysis was performed in eutopic endometrial samples from only a small number of patients and controls. In future investigations, a larger sample size should be used and the role of the other genes involved in the PTEN-PI3K/Akt signal transduction pathway should be analyzed.

Our findings revealed a possible involvement of the PTEN-PI3K/Akt-Bad axis in the pathogenesis of endometriosis, which may facilitate the discovery of suitable pathway inhibitors for disease treatment.

This study was supported by grants from the Science & Engineering Research Board (SERB), India (Lr No: SR/FT/LS-188/2009) to BM. The authors have no competing interests to declare.