Abstract
Clinical responses to the immmunomodulatory drug lenalidomide have been observed in patients with relapsed/refractory mantle cell lymphoma (MCL), although its mechanism of action remains partially unknown. We investigated whether the expression and subcellular localization of cyclin D1, a major cell-cycle regulator overexpressed in MCL, and the cyclin-dependent kinase inhibitor p27(KIP1), could identify MCL cases sensitive to lenalidomide, and whether the compound could modulate cyclin D1/p27(KIP1) complexes in MCL cells. MCL primary samples and cell lines were analyzed for subcellular levels of cyclin D1/p27(KIP1) complexes by Western blot, immunohistochemistry, immunoprecipitation, and flow cytometry. Activity of lenalidomide in vitro and its effect on cyclin D1/p27(KIP1) complexes were evaluated by real-time PCR, immunoprecipitation, immunofluorescence, and Western blot. In vivo validation was carried out in a mouse xenograft model of human MCL. We found cyclin D1 and p27(KIP1) to be coordinately expressed in all the MCL samples tested. Immunoprecipitation analyses and siRNA assays suggested a direct role of cyclin D1 in the regulation of p27(KIP1) levels. The nuclear accumulation of both proteins correlated with MCL cell tumorigenicity in vivo, and sensitivity to lenalidomide activity in vitro and in vivo. Lenalidomide mechanism of action relied on cyclin D1 downregulation and disruption of cyclin D1/p27(KIP1) complexes, followed by cytosolic accumulation of p27(KIP1), cell proliferation arrest, apoptosis, and angiogenesis inhibition. These results highlight a mechanism of action of lenalidomide in MCL cases with increased tumorigenicity in vivo, which is mediated by the dissociation of cyclin D1/p27(KIP1) complexes, and subsequent proliferation blockade and apoptosis induction.
Highlights
Mantle cell lymphoma (MCL) is an aggressive lymphoid neoplasm that accounts for 5% to 10% of all B-cell nonHodgkin lymphomas
Lenalidomide mechanism of action relied on cyclin D1 downregulation and disruption of cyclin D1/p27KIP1 complexes, followed by cytosolic accumulation of p27KIP1, cell proliferation arrest, apoptosis, and angiogenesis inhibition. These results highlight a mechanism of action of lenalidomide in MCL cases with increased tumorigenicity in vivo, which is mediated by the dissociation of cyclin D1/p27KIP1 complexes, and subsequent proliferation blockade and apoptosis induction
We find a tight correlation between contents of cyclin D1 and the cyclin-dependent kinase (CDK) inhibitor p27KIP1, underlying the sequestration of this latest in cyclin D1/CDK4 complexes, and protection from degradation. We show this phenomenon to be associated with increased tumorigenicity of MCL cells in vivo, and describe the possibility to counteract this process by using the thalidomide derivative, lenalidomide
Summary
These results highlight a mechanism of action of lenalidomide in MCL cases with increased tumorigenicity in vivo, which is mediated by the dissociation of cyclin D1/p27KIP1 complexes, and subsequent proliferation blockade and apoptosis induction.
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