Specific lentiviral shRNA-mediated knockdown of cyclin D1 in mantle cell lymphoma has minimal effects on cell survival and reveals a regulatory circuit with cyclin D2

Abstract

Cyclin D1 overexpression is the hallmark of mantle cell lymphoma (MCL). However, the importance of cyclin D1 in the maintenance and progression of the disease remains to be defined. The aim of this study was to elucidate the role of cyclin D1 overexpression using an efficient cyclin D1-shRNA and a lentiviral system in well-characterized MCL cell lines. Surprisingly, the knockdown of cyclin D1 led to a moderate retardation in growth, without induction of apoptosis. The cyclin D1-shRNA-transduced MCL cells showed a 15% shift from S phase to G 1 phase of the cell cycle, a weak induction of p27 Kip1 , decreased Rb (Ser807/811) phosphorylation, and a consistent upregulation of cyclin D2 mRNA and protein expression. However, double knockdown of cyclins D1 and D2 did not intensify the effects observed with cyclin D1 knockdown alone. These data suggest that the moderate effects of cyclin D1 downregulation on survival and proliferation are likely the result of compensatory cyclin-independent mechanisms governing proliferation or alternatively, secondary genetic events that make cyclin D1 dispensable. These findings have important implications for MCL therapy, as strategies targeting only cyclin D1 function might be hampered by compensatory regulatory mechanisms, resulting in a low probability of treatment response.

The impact of cyclin D1 mRNA isoforms, morphology and p53 in mantle cell lymphoma: p53 alterations and blastoid morphology are strong predictors of a high proliferation index

“…Furthermore, we have recently shown that siRNA-mediated knockdown of CyD1 in MCL cell lines has little influence on cell proliferation, because of a compensatory upregulation of cyclin D2. 55 Despite this heterogeneous picture concerning the role of CyD1 in lymphoma and although both high total CyD1 mRNA levels and predominance of the short mRNA transcript were found in all proliferation groups, we did observe a significant correlation for both parameters with a proliferation index >20%, and blastoid MCL cases were more likely to express the truncated D3'UTR; a phenomenon which has also been observed by others. 56 However, we failed to identify an association between high CyD1 levels or D3'UTR transcript predominance and overall survival.…”

Harnessing RNAi-based nanomedicines for therapeutic gene silencing in B-cell malignancies

“…The relevance of selective cycD1 silencing in MCL has been questioned before due to compensatory elevation of cyclin D2 expression (35,36). In accordance with precedent reports, we detected that the down-regulation of cycD1 expression induces a compensatory up-regulation of cyclin D2 expression (Fig.…”

Fenofibrate induces effective apoptosis in mantle cell lymphoma by inhibiting the TNFα/NF-κB signaling axis

“…It has been recently reported that inhibition of cyclin D1 in MCL cells Effects of fenofibrate on mantle cell lymphoma Z Zak et al blocks cell proliferation but is not sufficient to induce cell death in these cells. 35 Downregulation of cyclin D1 by PPARa agonist has been described in studies of human smooth muscle cells, 36 kidney cells 37 and cancer cells. 16,38 We decided to investigate whether fenofibrate has an effect on the regulation of cyclin D1.…”