摘要：

The chromosome translocation t(2;5)(p23;q25) results in the formation of a fusion gene of nucleophosmin-anaplastic lymphoma kinase (NPM-ALK), which is found in about 50% of anaplastic large-cell lymphomas (ALCLs). The fusion protein contains a constitutively activated ALK kinase that transforms cells through stimulating several mitogenic signaling pathways, such as phospholypase C-; STAT3- and STAT5; PI-3 kinase, and the recently identified Src kinase-mediated pathways. All these signaling events promote cell proliferation or anti-apoptosis effects. These data suggest that NPM-ALK plays an important role in regulating cancer cell growth and that inhibiting the action this fusion protein could be an effective cancer therapy. We developed an RNA interference system to efficiently and specifically down-regulate the expression of the fusion protein in lymphoma cell lines by designing NPM-ALK-targeting siRNA complementary to the breakpoint; therefore, an oncogene-specific gene targeting is accomplished in ALCL cells. Cell viability, proliferation, and apoptosis was measured after NPM–ALK repression. We observed a cancer type-specific viability loss only in t(2;5)-positive ALCL cell lines, SUDHL 1 and Karpas 299, but not in lymphoma cells lacking the chromosome translocation, Jurkat and Granta 519. Dual mechanisms were identified in causing viability loss, including down-regulated cell proliferation and modestly increased cell apoptosis. Chemotherapy drug, doxorubicin, induced cell apoptosis increased synergistically with NPM-ALK repression, suggesting NPM-ALK repression sensitizes the ALCL cells to chemotherapy. A prolonged effect on cell growth was observed in the ALCL cells, noting lower colony formation ability associated with the siRNA-mediated temporary gene targeting. These results reveal the importance of continuous NPM-ALK expression in maintaining lymphoma cell growth, and suggest a novel combinational therapy specifically for NPM-ALK-positive ALCLs aimed at repressing the fusion gene with chemotherapy treatment.

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