Differential expression of novel naturally occurring splice variants of PTEN and their functional consequences in Cowden syndrome and sporadic breast cancer.
PTEN, a dual-phosphatase tumor suppressor, is inactivated in Cowden syndrome (CS), characterized by high risk of breast and thyroid cancer, and in variety of sporadic cancers. Despite the importance of alternative splicing, very limited information on its role in PTEN and associated cancers is available. We identified eight novel PTEN splice variants (SVs) that retained intron 3 regions (3a, 3b, 3c); intron 5 regions (5a, 5b, 5c); excluded part of exon 5 (DelE5) or all of exon 6 (DelE6), respectively. Analysis of SVs in 12 sporadic breast cancers revealed full-length (FL)-PTEN transcript reduction in 10; SVs 3b, 3c and 5c not expressed in 7, 6 and 4, respectively, and under-expressed in the rest. In contrast, SV-5b was over-expressed in breast cancers. PTEN SV analysis in 16 CS/CS-like patients and eight controls revealed that SV-5a is under-expressed and SV-3a over-expressed in the germline of CS/CS-like individuals when compared with controls. Although SV-5a expression decreased P-Akt level and cyclin D1 promoter activity, SVs 5b and 5c increased cyclin D1 promoter activity. Thus, SV-5a behaving like FL-PTEN corroborates our observation that SV-5a is under-expressed in CS when compared with controls. Similarly, SV-5b functionally counters PTEN's action and is over-expressed in sporadic breast cancers. Furthermore, we demonstrate that expression of these SVs is under the regulation of p53. Our observations suggest that differential expression of PTEN and its SVs could play a role in the pathogenesis of sporadic breast cancers and CS, and may lend a novel way of making a rapid molecular diagnosis of CS without mutation analysis.
Agrawal
Shipra
S
Genomic Medicine Institute, Cleveland Clinic Lerner College of Medicine, 9500 Euclid Avenue, Mailcode NE-50, Cleveland, OH 44195, USA.
Eng
Charis
C
D017398:Alternative Splicing; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000209:etiology / Q000235:genetics* / Q000378:metabolism; D016022:Case-Control Studies; D045744:Cell Line, Tumor; D003001:Cloning, Molecular; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D005333:Fetus; D017930:Genes, Reporter; D014644:Genetic Variation; D006223:Hamartoma Syndrome, Multiple / Q000209:etiology / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D008297:Male; D051059:PTEN Phosphohydrolase / Q000235:genetics / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D013577:Syndrome; D014018:Tissue Distribution
D008156:Luciferases; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human