Erratum to: PDK1-mTOR signaling pathway inhibitors reduce cell proliferation in MK2206 resistant neuroblastoma cells.

[This corrects the article DOI: 10.1186/s12935-015-0239-4.].

PDK1-mTOR signaling pathway inhibitors reduce cell proliferation in MK2206 resistant neuroblastoma cells.

PURPOSE: AKT plays a pivotal role in the signal transduction of cancer cells. MK2206, an AKT inhibitor, has been shown to be an effective anti-cancer drug to a variety of cancer cell lines. However, some cancer cells acquire resistance to MK2206 and new strategies to suppress these cell lines remain to be developed. EXPERIMENTAL DESIGN: Acquired MK-2206-resistant neuroblastoma (NB) cell sublines were induced by stepwise escalation of MK-2206 exposure (4-12 weeks). MTT assay was used to validate cell proliferation. Flow cytometry was performed for cell cycle analysis. Western blot assay was used for cell signaling study. RESULTS: MK2206 (5-10 µmol) significantly suppressed cell growth of MK2206 non-resistant NB cells (LAN-1, KP-N-SIFA, NB-19 and SK-N-DZ), but is less efficient in inhibiting that of resistant sublines, even after 2-week MK2206-free incubation. MK2206 acted in mTOR-S6K dependent and independent methods. MK-2206 resistant sublines (LAN-1-MK, KP-N-SIFA-MK, and SK-N-DZ-MK) showed lower IC50 of GSK2334470 (PDK1 inhibitor). The cell growth of all sublines was prohibited by AZD8805 (mTOR inhibitor), with IC50 of AZD8805 3-10 times lower than MK2206 non-resistant cells. The signaling profiles of these resistant sublines were characterized by elevated PDK1-mTOR-S6K activity, accompanying by low phosphorylation of AKT compared with non-resistant counterparts. GSK2334470 and AZD8055 effectively inhibited phosphorylation of PDK1 and mTOR, respectively, and induced higher G0-G1 ratio in LAN-1-MK than that in LAN-1 as well. PDK1 and mTOR inhibitors effected on phosphorylation of GSK3ß in some of resistant sublines. CONCLUSION: NB cells can acquire MK2206 resistance after exposure for 4-12 weeks. Resistant cells feature reliance on PDK1-mTOR-S6K pathway and are more sensitive to PDK1 and mTOR inhibitors than the non-resistant counterparts. Thus, suppression of PDK1-mTOR-S6K signaling pathway is an effective way to overcome the MK2206 resistance, and this may be a promising strategy for targeted therapy.

Heterogeneity of neuroblastoma cell lines in insulin-like growth factor 1 receptor/Akt pathway-mediated cell proliferative responses.

Insulin-like growth factor 1 receptor (IGF-1R) is critical for cancer cell proliferation; however, recent clinical anti-IGF-1R trials did not show clear clinical benefit in cancer therapy. We hypothesized that IGF-1R signaling-mediated proliferative response is heterogeneous in neuroblastoma (NB) cells, and analyzed the cell growth of 31 NB cell lines cultured in three different media, including Hybridoma-SFM medium (with insulin) and RPMI1640 with/without 10% FBS. Three growth patterns were found. In response to IGF and insulin, cell proliferation and Akt phosphorylation were upregulated in 13 cell lines, and suppressed by MK2206 (Akt inhibitor) and picropodophyllin (IGF-1R inhibitor). Interestingly, 3 of these 13 cell lines showed Akt self-phosphorylation and cell proliferation in RPMI1640; their proliferation was downregulated by anti-IGF-1 or anti-IGF-2 neutralizing antibody, suggesting the existence of an autocrine loop in the IGF-1R/Akt pathway. Eighteen NB cell lines did not proliferate in RPMI1640, even though Akt phosphorylation was upregulated by IGF and insulin. Based on the heterogeneous response of the IGF-1R/Akt pathway, the 31 NB cell lines could be classified into group 1 (autocrine IGF-mediated), group 2 (exogenous IGF-mediated) and group 3 (partially exogenous IGF-mediated) NB cell lines. In addition, group 3 NB cell lines were different from group 1 and 2, in terms of serum starvation-induced caspase 3 cleavage and picropodophyllin-induced G2/M arrest. These results indicate that the response of the IGF-1R/Akt pathway is an important determinant of the sensitivity to IGF-1R antagonists in NB. To our knowledge, this is the first report describing heterogeneity in the IGF-1R/Akt-mediated proliferation of NB cells.

Functional studies of a novel germline p53 splicing mutation identified in a patient with Li-Fraumeni-like syndrome.

Most p53 mutations identified in Li-Fraumeni syndrome (LFS) are missense mutations; splicing mutations have rarely been reported. A novel splicing p53 mutation was identified in a patient with Li-Fraumeni-like syndrome (LFL). Usually, p53 missense mutants identified in LFS and cancer cells function as dominant negative mutations interfering with wild-type p53 function. However, the mechanism by which p53 haploinsufficiency causes carcinogenesis is not well characterized. In this study, we describe a novel splicing mutation that results in the loss-of-function of p53. These findings suggest a linkage between the loss-of-function type p53 mutation and a LFL phenotype.

Novel p53 splicing site mutation in Li-Fraumeni-like syndrome with osteosarcoma.

We describe a 15-year-old girl with a novel germline p53 splice site mutation who developed an osteosarcoma. She received several cycles of chemotherapy with complete resection of the primary tumor without amputation, and has maintained remission for 18 months. Li-Fraumeni-like syndrome was suspected based on familial history. Sequence analysis revealed the presence of a novel germline p53 gene mutation resulting in a G to A transition at position +1 at the donor splice site of intron 6, creating a 6 amino acid insertion. This case provides interesting insight into the phenotype-genotype correlation in LFL syndrome with a TP53 splicing mutation.

Role of microRNAs in glucocorticoid­resistant B­cell precursor acute lymphoblastic leukemia.

Acute lymphoblastic leukemia (ALL) is the most common malignant disorder in children and intensive combination therapy has markedly improved patient prognosis. However, efficacy of the treatment still fails in 10­15% of patients. Glucocorticoids (GCs) such as prednisone and dexamethasone (DEX) are essential drugs used for ALL chemotherapy, and the response to GC treatment is a strong independent factor of ALL prognosis. In the present study, we examined the mechanism of GC resistance of B­cell precursor ALL (BCP­ALL). As determined by RT­qPCR and western blot analyses, GC treatment upregulated glucocorticoid receptor (GR) protein and Bcl­2­interacting mediator of cell death (BCL2L11, BIM) protein expression, resulting in apoptosis of a GC­sensitive BCP­ALL cell line, but not of a GC­resistant BCP­ALL cell line as shown by flow cytometry. GR was downregulated in a DEX­resistant BCP­ALL cell line which was induced by treatment of cells with increasing concentrations of DEX. Importantly, expression levels of miR­142­3p and miR­17~92 cluster were upregulated in the BCP­ALL cell line with acquired DEX resistance as examined by RT­qPCR. Our results suggest that interference of miR­142­3p and miR­17~92 may overcome the resistance of BCP­ALL to GCs.