A New Phosphatase Involved in Human Carcinomas: Laforin Is Downregulated in a Large Set of Tumors, Supporting Its Role as Tumor Suppressor
MA Vazquez, C Parada, J Hernandez, S Landolfi, V Peg, R Somoza, S Rodriguez de Cordoba, S Ramon y Cajal. HU Vall Hebron, Barcelona, Spain; CSIC, Madrid, Spain
Background: A large number of molecular alterations have been described in cancer. Importantly, very few phosphatases, like PTEN, have been described so far to be involved in human tumors. Recently, Laforin was associated with T-Lymphomas in an inmunocompromised mouse model. Laforin is a ubiquitous protein encoded by the EPM2A gene with a critical role in glycogen metabolism, and is mutated in at least 50% of the patients with progressive myoclonus epilepsy (Lafora disease). This protein contains a dual-specificity protein phosphatase domain, and has been linked to GSK3 dephosphorylation.
Design: We have studied the expression levels of Laforin by WB and real-time PCR in 58 Colorectal Adenocarcinomas, 15 Clear-Cell Renal Carcinomas, 10 Astrocytomas, 15 Lung carcinomas and 25 Breast Carcinomas. Colon, kidney and lung samples were compared with normal adjacent tissue, Breast carcinomas and Astrocytomas were compared to pooled normal tissue. Five adenomas adjacent to colorectal adenocarcinomas were also studied. Cell lines derived from breast (MDA-MB-231 and 435) and colon cancer (HCA7 and HT29) were infected with retroviruses to induce overexpression of Laforin, and cell growth was measured by the Population Doubling technique.
Results: Laforin protein was reduced or absent in 80% of colorectal adenocarcinomas, 80% clear-cell renal carcinomas, and 40% breast carcinomas. Similar results were obtained by real-time PCR. No concomitant increase in GSK3 phosphorylation was observed. Conversely, no significant decrease in Laforin expression was observed in Astrocytomas. Laforin mRNA and protein levels were lower in adenocarcinoma than in polyps, and lower in polyps than in normal tissue, hinting a gradual reduction in Laforin during the development of colorectal cancer. Finally, the overexpression of Laforin in transformed cell lines reduced the proliferation index.
Conclusions: A striking lack of Laforin protein was observed in a large number of colon and kidney carcinomas, thus presenting a role for a novel phosphatase in a large set of human tumors. We propose that Laforin may be a tumor suppressor gene that is downregulated in early steps of tumor development.
Tuesday, March 10, 2009 1:00 PM
Poster Session IV # 215, Tuesday Afternoon