Down-regulation of Cyclin D3 by Small-interfering RNA Induces Cell Cycle Arrest and Apoptosis through the Dissociation of p27Kip1 in a t(6; 14) (p21; q32) Positive Myeloma Cell Line

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Translocation of chromosome t (6 ; 14) (p21 ; q32) results in overexpression of the cyclin D3 gene (CCND3), and is a recurrent genetic alteration in multiple myeloma. To elucidate the biological role of the overexpression of the cyclin D3 protein (CCND3) in t (6 ; 14) (p21 ; q32), we transfected a CCND3-specific, small-interfering RNA (siRNA) into KMM-1 cells carrying t (6 ; 14) (p21 ; q32). Following transfection, CCND3 expression levels decreased with maximal effect after 24 hours. While CCND3 expression was down regulated the rate of proliferation in transfected KMM-1 cells was half that in control cells. Cell-cycle analysis revealed that transfection resulted in transition fron G1 to S being blocked, and the transfected cells underwent apoptosis. Immunoprecipitation experiments demonstrated that CCND3 formed a complex with the majority of p27kip1 in KMM-1 cells under steady-state conditions. When CCND3 expression was down regulated the P27kip1 shifted to cyclin E protein (CCNE) and formed a complex. Our results show that CCND3 is essential for the cellular growth of t (6 ; 14) (p21 ; q32)-positive myelomas and that CCND3 sequesters p27kip1 from CCNE, resulting in functional inactivation of its anti-proliferative role. Modification of CCND3 and p27kip1 interaction may be a novel therapeutic approach for t (6 ; 14) (p21 ; q32)-positive myeloma.