Alteration of G1 cell-cycle protein expression and induction of p53 but not p21/waf1 by the DNA-modifying carcinogen 2-acetylaminofluorene in growth-stimulated hepatocytes in vitro

Molecular mechanism of G1 arrest and cellular senescence induced by LEE011, a novel CDK4/CDK6 inhibitor, in leukemia cells

Background

Overexpression of cyclin D1 dependent kinases 4 and 6 (CDK4/6) is a common feature of many human cancers including leukemia. LEE011 is a novel inhibitor of both CDK4 and 6. To date, the molecular function of LEE011 in leukemia remains unclear.

Methods

Leukemia cell growth and apoptosis following LEE011 treatment was assessed through CCK-8 and annexin V/propidium iodide staining assays. Cell senescence was assessed by β-galactosidase staining and p16^INK4a expression analysis. Gene expression profiles of LEE011 treated HL-60 cells were investigated using an Arraystar Human LncRNA array. Gene ontology and KEGG pathway analysis were then used to analyze the differentially expressed genes from the cluster analysis.

Results

Our studies demonstrated that LEE011 inhibited proliferation of leukemia cells and could induce apoptosis. Hoechst 33,342 staining analysis showed DNA fragmentation and distortion of nuclear structures following LEE011 treatment. Cell cycle analysis showed LEE011 significantly induced cell cycle G₁ arrest in seven of eight acute leukemia cells lines, the exception being THP-1 cells. β-Galactosidase staining analysis and p16^INK4a expression analysis showed that LEE011 treatment can induce cell senescence of leukemia cells. LncRNA microarray analysis showed 2083 differentially expressed mRNAs and 3224 differentially expressed lncRNAs in LEE011-treated HL-60 cells compared with controls. Molecular function analysis showed that LEE011 induced senescence in leukemia cells partially through downregulation of the transcriptional expression of MYBL2.

Conclusions

We demonstrate for the first time that LEE011 treatment results in inhibition of cell proliferation and induction of G₁ arrest and cellular senescence in leukemia cells. LncRNA microarray analysis showed differentially expressed mRNAs and lncRNAs in LEE011-treated HL-60 cells and we demonstrated that LEE011 induces cellular senescence partially through downregulation of the expression of MYBL2. These results may open new lines of investigation regarding the molecular mechanism of LEE011 induced cellular senescence.

Electronic supplementary material

The online version of this article (doi:10.1186/s12935-017-0405-y) contains supplementary material, which is available to authorized users.

Impaired nuclear accumulation and shortened phosphorylation of ERK after growth factor stimulation in cultured hepatocytes from rats exposed to 2-acetylaminofluorene

The hepatic carcinogen 2-acetylaminofluorene (AAF) exerts its effect as a tumor promoter by mitoinhibition of normal hepatocytes. Initiated cells proliferate selectively and develop into preneoplastic foci and subsequently into carcinomas. To study whether some of the mitoinhibitory effects of AAF could be attributed to an influence on intracellular signal transduction, growth factor signaling was studied in cultured hepatocytes from rats fed AAF for 7 d. Activation through the epidermal growth factor receptor (EGFR) was used to probe possible changes in downstream mitogenic signaling mechanisms. The proliferative response to epidermal growth factor (EGF), measured as proliferating cell nuclear antigen expression and thymidine incorporation, was almost completely inhibited in hepatocytes exposed to AAF. Neither EGFR protein levels nor EGF binding was notably altered in AAF-exposed hepatocytes as opposed to normal hepatocytes. The initial tyrosine phosphorylation of EGFR and downstream activation of Sos, Raf-1, and extracellular signal-regulated protein kinase (ERK) were similar in AAF-treated and control hepatocytes. Even though ERK phosphorylation was unaffected, a remarkable (80%) reduction of ERK nuclear accumulation was observed in AAF-exposed hepatocytes immediately after mitogen stimulation. EGFR tyrosine phosphorylation and downstream signaling lasted 6 h in control cells versus 2 h in AAF-exposed hepatocytes. We previously demonstrated that AAF inhibits the growth factor-dependent induction of cyclin D1 and arrests hepatocyte cell-cycle progression before the p21/CIP1-controlled DNA-damage check point. The present data indicate that the DNA-damaging carcinogen AAF induces growth inhibition by a distinct inhibition of ERK nuclear accumulation after mitogen stimulation. Inhibition of intracellular signal transduction may represent a novel mechanism of growth arrest. Mol. Carcinog. 28:84-96, 2000.