Panhandle PCR amplifies genomic DNA with known 5 and unknown 3 sequences from a template with an intrastrand loop schematically shaped like a pan with a handle. We used panhandle PCR to clone MLL genomic breakpoints in two pediatric treatment-related leukemias. The karyotype in a case of treatment-related acute lymphoblastic leukemia showed the t(4;11)(q21;q23). Panhandle PCR amplified the translocation breakpoint at position 2158 in intron 6 in the 5 MLL breakpoint cluster region (bcr). The karyotype in a case of treatment-related acute myeloid leukemia was normal, but Southern blot analysis showed a single MLL gene rearrangement. Panhandle PCR amplified the breakpoint at position 1493 in MLL intron 6. Screening of somatic cell hybrid and radiation hybrid DNAs by PCR and reverse transcriptase-PCR analysis of the leukemic cells indicated that panhandle PCR identified a fusion of MLL intron 6 with a previously uncharacterized sequence in MLL intron 1, consistent with a partial duplication. In both cases, the breakpoints in the MLL bcr were in Alu repeats, and there were Alu repeats in proximity to the breakpoints in the partner DNAs, suggesting that Alu sequences were relevant to these rearrangements. This study shows that panhandle PCR is an effective method for cloning MLL genomic breakpoints in treatment-related leukemias. Analysis of additional pediatric cases will determine whether breakpoint distribution deviates from the predilection for 3 distribution in the bcr that has been found in adult cases.DNA topoisomerase II catalyzes transient cleavage and rejoining of both strands of the DNA double helix (1). Epipodophyllotoxins form a complex with the DNA and DNA topoisomerase II, decrease DNA rejoining, and cause chromosomal breakage (2). Epipodophyllotoxins and other DNA topoisomerase II inhibitors are associated with leukemias with translocations of a breakpoint cluster region (bcr) of the MLL gene at chromosome band 11q23 (3-10). One suggested model for the translocations involving MLL entails DNA topoisomerase II-mediated chromosomal breakage followed by fusion of DNA free ends from different chromosomes through DNA repair (11). A better understanding of the translocation mechanism may come through genomic breakpoint cloning in many other cases.However, MLL genomic breakpoint cloning by PCR is difficult because MLL has myriad partner genes, and karyotype analysis does not detect the rearrangement or give information about potential translocation partners in onethird of cases (8). Other rearrangements result from partial duplication of several exons of the MLL gene (12-19). Panhandle PCR amplifies genomic DNA with known 5Ј and unknown 3Ј sequences and does not require specific primers for the many partner genes of MLL (20,21). In the present study, we used panhandle PCR to surmount the problem of MLL genomic breakpoint cloning in two pediatric DNA topoisomerase II inhibitor-related leukemias. To validate the method, we first used panhandle PCR in a treatment-related leukemia in which the cytogeneti...

The phosphatidylinositol 3-kinase/AKT pathway is crucial to many cell functions, and its dysregulation in tumors is a common finding. The molecular basis of follicular thyroid cancer metastasis is not well understood but may also be influenced by AKT activation. We previously created a knockin mutant mouse that expresses a mutant thyroid hormone receptor-beta gene (TRbetaPV mouse) that spontaneously develops thyroid cancer and distant metastasis similar to human follicular thyroid cancer. In this study, we investigated whether our mouse model exhibits similar AKT activation as human follicular thyroid cancer. Western blot analysis on thyroids from both wild-type and TRbeta(PV/PV) mice revealed elevation of activated AKT in TRbeta(PV/PV) mice. Immunohistochemistry and confocal microscopy reveal activated AKT in both the thyroid and metastatic lesions of TRbeta(PV/PV) mice. Whereas all three AKT isoforms were overexpressed in primary tumors from TRbeta(PV/PV) mice in the cytoplasm of thyroid cancer cells, only AKT1 was also found in the nucleus, matching the localization of activated AKT in a pattern similar to human follicular thyroid cancer. In the metastases, all AKT isoforms correlated with phosphorylated AKT nuclear localization. We created primary thyroid cell lines derived from TRbeta(PV/PV) mice and found reduction of phosphorylated AKT levels or AKT downstream targets diminishes cell motility. Activated AKT is common to both human and mouse follicular thyroid cancer and is correlated with increased cell motility in vitro and metastasis in vivo. Thus, TRbeta(PV/PV) mice could be used to further dissect the detailed pathways underlying the progression and metastasis of follicular thyroid carcinoma.