Combined Depletion of Cell Cycle and Transcriptional Cyclin-Dependent Kinase Activities Induces Apoptosis in Cancer Cells

Abstract

Selective cyclin-dependent kinase (cdk) 2 inhibition is readily compensated. However, reduced cdk2 activity may have antiproliferative effects in concert with other family members. Here, inducible RNA interference was used to codeplete cdk2 and cdk1 from NCI-H1299 non-small cell lung cancer and U2OS osteosarcoma cells, and effects were compared with those mediated by depletion of either cdk alone. Depletion of cdk2 slowed G 1 progression of NCI-H1299 cells and depletion of cdk1 slowed G 2 -M progression in both cell lines, with associated endoreduplication in U2OS cells. However, compared with the incomplete cell cycle blocks produced by individual depletion, combined depletion had substantial consequences, with G 2 -M arrest predominating in NCI-H1299 cells and apoptosis the primary outcome in U2OS cells. In U2OS cells, combined depletion affected RNA polymerase II expression and phosphorylation, causing decreased expression of the antiapoptotic proteins Mcl-1 and X-linked inhibitor of apoptosis (XIAP), effects usually mediated by inhibition of the transcriptional cdk9. These events do not occur after individual depletion of cdk2 and cdk1, suggesting that reduction of cdk2, cdk1, and RNA polymerase II activities all contribute to apoptosis in U2OS cells. The limited cell death induced by combined depletion in NCI-H1299 cells was significantly increased by codepletion of cdk9 or XIAP or by simultaneous treatment with the cdk9 inhibitor flavopiridol. These results show the potency of concomitant compromise of cell cycle and transcriptional cdk activities and may guide the selection of clinical drug candidates. (Cancer Res 2006; 66(18): 9270-80)

The cyclin-dependent kinase inhibitor SNS-032 has single agent activity in AML cells and is highly synergistic with cytarabine

“…9 Deregulated progression through the cell cycle is a hallmark of malignant transformation. 8,[10][11][12] CDK7 complexes with cyclin H and is involved in cell-cycle regulation as the catalytic subunit of CDK activating kinase, which activates CDKs 1, 2, 4 and 6 by phosphorylation and is essential for mitosis. 8,[13][14][15] Transcriptional CDKs, including CDK7 and 9, promote the initiation and elongation of nascent RNA transcripts.…”

“…8,[13][14][15] Transcriptional CDKs, including CDK7 and 9, promote the initiation and elongation of nascent RNA transcripts. 7,10 In addition to its role in the cell cycle, CDK7 is an integral part of transcription factor II H (TFIIH) transcription factor, which phosphorylates serine 5 in the carboxy terminal domain of RNA polymerase II (RNA Pol II) to facilitate transcription initiation. 16 CDK9, as part of elongation factor P-TEFb, phosphorylates serine 2 in RNA Pol II, which is required for elongation.…”

Biological characterization of AT7519, a small-molecule inhibitor of cyclin-dependent kinases, in human tumor cell lines

“…This theory is backed up by the observation that the knockout of individual E/A-type cyclins results in an embryonic lethal phenotype (21). Further data showed that depletion of CDK1 or CDK2 alone by RNA interference in human cancer cells was insufficient to cause complete cell cycle blockade (22). Combined depletion of the CDKs had a markedly increased effect resulting in either G 2 -M blockade or induction of apoptosis depending on the cell line in question.…”

Review of the Molecular Pathogenesis of Osteosarcoma

“…In the human OSA cell line U-2OS, combined depletion of CDK1 and CDK2 but not anyone alone by RNA silencing has been proved to arrest cells in G2-M phase and to induce apoptosis (Hu et al, 2001;Cai et al, 2006;Wei et al, 2011).…”