Frequent loss of PTEN expression is linked to elevated phosphorylated Akt levels, but not associated with p27 and cyclin D1 expression, in primary epithelial ovarian carcinomas

PTEN (MMAC1/TEP1), a tumor suppressor gene on chromosome subband 10q23.3, i s variably mutated and/or deleted in a variety of human cancers. Germline m utations in PTEN, which encode a dual-specificity phosphatase, have been im plicated in at least two hamartoma tumor syndromes that exhibit some clinic al overlap, Cowden syndrome and Bannayan-Riley-Ruvalcaba syndrome. Among se veral series of ovarian cancers, the frequency of loss of heterozygosity (L OH) of markers nanking and within PTEN, is similar to 30 to 50%, and the so matic intragenic PTEN mutation frequency is < 10%. In this study, we screen ed primary adenocarcinomas of the ovary for LOH of polymorphic markers with in and flanking the PTEN gene and for intragenic mutations of the PTEN gene and compared them to PTEN expression using immunohistochemistry. Furthermo re, we sought to detect the expression of the presumed downstream targets o f PTEN, such as P-Akt, p27, and cyclin D1 by immunohistochemistry. LOH at 1 0q23 was observed in 29 of 64 (45%) cases. Of the 117 samples, 6 somatic in tragenic PTEN mutations, 1 germline mutation, and 1 novel polymorphism were found in 7 (6%) patients. Immunostaining of 49 ovarian cancer samples reve aled that 13 (27%) were PTEN immunostain-negative, 25 (51%) had reduced sta ining, and the rest (22%) were PTEN expression-positive. Among the 44 infor mative tumors assessed for 10q23 LOH and PTEN immunostaining, there was an association between 10q23 LOH and decreased or absent staining (P = 0.0317) . Of note, there were five (11%) tumors with neither mutation nor deletion that exhibited no PTEN expression and 10 (25%) others without mutation or d eletion but had decreased PTEN expression. Among the 49 tumors available fo r immunohistochemistry, 28 (57%) showed P-Akt-positive staining, 24 (49%) h ad decreased p27 staining, and cyclin D1 was overexpressed in 35 (79%) case s. In general, P-Akt expression was inversely correlated with PTEN expressi on (P = 0.0083). These data suggest that disruption of PTEN by several mech anisms, allelic loss, intragenic mutation, or epigenetic silencing, all con tribute to epithelial ovarian carcinogenesis, and that epigenetic silencing is a significant mechanism. The Akt pathway is prominently involved, but c learly not in all cases. Surprisingly, despite in vitro demonstration that p27 and cyclin D1 lies downstream of PTEN and Akt, there was no correlation between p27 and cyclin D1 expression and PTEN or P-Akt status. Thus, in vi vo, although PTEN and Akt play a prominent role in ovarian carcinogenesis, p27 and cyclin D1 might not be the primary downstream targets. Alternativel y, these observations could also suggest that pathways involving other than Akt, p27 and cyclin D1 that Lie downstream of PTEN play roles in ovarian c arcinogenesis.