Characterization of Cyclin E Expression in Multiple Myeloma and Its Functional Role in Seliciclib-Induced Apoptotic Cell Death

Abstract

Multiple Myeloma (MM) is a lymphatic neoplasm characterized by clonal proliferation of malignant plasma cell that eventually develops resistance to chemotherapy. Drug resistance, differentiation block and increased survival of the MM tumor cells result from high genomic instability. Chromosomal translocations, the most common genomic alterations in MM, lead to dysregulation of cyclin D, a regulatory protein that governs the activation of key cell cycle regulator – cyclin dependent kinase (CDK). Genomic instability was reported to be affected by over expression of another CDK regulator - cyclin E (CCNE). This occurs early in tumorigenesis in various lymphatic malignancies including CLL, NHL and HL. We therefore sought to investigate the role of cyclin E in MM. CCNE1 expression was found to be heterogeneous in various MM cell lines (hMMCLs). Incubation of hMMCLs with seliciclib, a selective CDK-inhibitor, results in apoptosis which is accompanied by down regulation of MCL1 and p27. Ectopic over expression of CCNE1 resulted in reduced sensitivity of the MM tumor cells in comparison to the paternal cell line, whereas CCNE1 silencing with siRNA increased the cell sensitivity to seliciclib. Adhesion to FN of hMMCLs was prevented by seliciclib, eliminating adhesion–mediated drug resistance of MM cells. Combination of seliciclib with flavopiridol effectively reduced CCNE1 and CCND1 protein levels, increased subG1 apoptotic fraction and promoted MM cell death in BMSCs co-culture conditions, therefore over-coming stroma-mediated protection. We suggest that seliciclib may be considered as essential component of modern anti MM drug combination therapy.

The homeobox transcription factor MEIS2 is a regulator of cancer cell survival and IMiDs activity in Multiple Myeloma: modulation by Bromodomain and Extra-Terminal (BET) protein inhibitors

“…3a) and confirmed in (Agnelli - R = 0.541 and Chng - R = 0.384 MM Datasets of R2) (Supplementary Figure 5) 42,43 , a regulatory subunit of Cyclin-Dependent Kinase 2 (CDK2). In this regard, MM cells have been shown to be sensitive to CDK inhibition by various chemical inhibitors such as Flavopiridol, SNS-032, P276–00 and Seliciclib/Roscovitine 44 , able to induce cell cycle arrest and apoptosis by downregulation of anti-apoptotic proteins such as MCL1 44 . In particular, a pro-apoptotic response of MM cells to Seliciclib/Roscovitine inversely correlates to Cyclin E/CCNE1 expression levels 44 .…”

“…In this regard, MM cells have been shown to be sensitive to CDK inhibition by various chemical inhibitors such as Flavopiridol, SNS-032, P276–00 and Seliciclib/Roscovitine 44 , able to induce cell cycle arrest and apoptosis by downregulation of anti-apoptotic proteins such as MCL1 44 . In particular, a pro-apoptotic response of MM cells to Seliciclib/Roscovitine inversely correlates to Cyclin E/CCNE1 expression levels 44 . In agreement with the positive correlation observed in the Hanamura MM Dataset, our data indicate that reduced levels of MEIS2 in wt-SKO-007(J3) cells obtained by transient transduction of validated shRNA sequences, significantly repressed mRNA expression of Cyclin E/CCNE1 in these cells (Fig.…”

The therapeutic potential of cell cycle targeting in multiple myeloma

“…Flavopiridol was also shown to synergistically enhance the anti-myeloma effect of Bcl-2 antagonists, bortezomib and TRAIL, while seliciclib potentiates the anti-myeloma activity of doxorubicin and bortezomib [ 88 , 90 – 92 ]. Of interest, the sensitivity of myeloma cells to seliciclib was reported to be associated with cyclin E1 expression; with high cyclin E1 expression correlating with a low sensitivity [ 93 ]. Moreover, low p18 expression is also associated with a better response to seliciclib in myeloma cells [ 94 ].…”

Cyclin-dependent kinase inhibitor therapy for hematologic malignancies

“…Seliciclib potently down-regulates Mcl-1 via inhibition of transcription, triggering apoptosis in human leukemia and MM cells (17, 18, 21). In human MM cell lines, seliciclib induces apoptosis accompanied by down-regulation of Mcl-1 and p27, and eliminates adhesion-mediated drug resistance (59). Seliciclib exposure of human diffuse large B-cell lymphoma (DLBCL) cells results in G1- and G2/M-phase arrest and induction of apoptosis independently of underlying chromosomal translocations (60).…”