A recurrent activating missense mutation in Waldenström macroglobulinemia affects the DNA binding of the ETS transcription factor SPI1 and enhances proliferation

The ETS-domain transcription factors divide into subfamilies based on protein similarities, DNA binding sequences and interaction with cofactors. They are regulated by extracellular clues and contribute to cellular processes, including proliferation and transformation. ETS genes are targeted through genomic rearrangements in oncogenesis. The PU.1/SPI1 gene is inactivated by point mutations in human myeloid malignancies. We identified a recurrent somatic mutation (Q226E) in PU.1/SPI1 in Waldenstrom macroglobulinemia, a B-cell lymphoproliferative disorder. It affects the DNA binding affinity of the protein and allows the mutant protein to bind and activate more frequently promoter regions with respect to wild type protein. Mutant SPI1 binding at promoters activates gene-sets typically promoted by other ETS factors, resulting in enhanced proliferation and decreased terminal B-cell differentiation in model cell lines and primary samples. In summary, we describe oncogenic subversion of transcription factor function through subtle alteration of DNA binding leading to cellular proliferation and differentiation arrest

Farnesyltransferase inhibitor R115777 inhibits cell growth and induces apoptosis in mantle cell lymphoma.

International audienceINTRODUCTION: The cytotoxic activity of the farnesyltranseferase inhibitor R115777 was evaluated in cell lines representative of mantle cell lymphoma (MCL). METHODS: Cell growth, proliferation, and apoptosis were analyzed in four human MCL cell lines (Granta, NCEB, REC, and UPN1) in presence of R115777, alone or in combination with vincristin, doxorubicin, bortezomib, cisplatin and cytarabine. Inhibition of farnesylation was determined by the appearance of prelamin A. The antitumor activity of R115777, administered p.o. at 100, 250 and 500 mg/kg, was determined in vivo in nude mice xenografted with UPN1 cells. RESULTS: R115777 inhibited the growth of MCL cell lines in vitro with inhibitory concentrations ranging between 2 and 15 nM. A fifty percent decrease of cell viability was observed at concentrations comprised between 0.08 and 17 microM. Apoptosis, evaluated by annexin V and activated caspase 3 staining, was induced in all cell lines, in 40 to 71% of the cells depending on the cell lines. In addition, R115777 significantly increased the cytotoxic effect of vincristine, doxorubicin, bortezomib, cisplatin and cytarabine (p=0.001, p=0.016, p=0.006, p=0.014 and p=0.007 respectively). Exposure of MCL cell lines to R115777 during 72 hours resulted in inhibition of protein farnesylation. R115777 administered p.o. twice daily for 8 consecutive days to mice bearing established s.c. UPN1 xenograft displayed cytostatic activity at the 500 mg/kg dosage. CONCLUSION: We have demonstrated that inhibition of farnesyltransferase by R115777 was associated with growth inhibition and apoptosis of MCL cell lines in vitro and tumor xenograft stability in vivo