MYCN amplification in human cancers predicts poor prognosis and resistance to therapy. However, pharmacological strategies that directly target N-Myc, the protein encoded by MYCN, remain elusive. Here, we identify a molecular mechanism responsible for reciprocal activation between Polo-like kinase-1 (PLK1) and N-Myc. PLK1 specifically binds to the SCF ubiquitin ligase, phosphorylates it, and promotes its autopolyubiquitination and proteasomal degradation, counteracting Fbw7-mediated degradation of N-Myc and additional substrates, including cyclin E and Mcl1. Stabilized N-Myc in turn directly activates PLK1 transcription, constituting a positive feedforward regulatory loop that reinforces Myc-regulated oncogenic programs. Inhibitors of PLK1 preferentially induce potent apoptosis of MYCN-amplified tumor cells from neuroblastoma and small cell lung cancer and synergistically potentiate the therapeutic efficacies of Bcl2 antagonists. These findings reveal a PLK1-Fbw7-Myc signaling circuit that underlies tumorigenesis and validate PLK1 inhibitors, alone or with Bcl2 antagonists, as potential effective therapeutics for MYC-overexpressing cancers.

Amplification of the MYCN gene in human neuroblastoma predicts poor prognosis and resistance to therapy. We previously showed that MYCN-amplified neuroblastoma cells constantly require large amounts of glutamine to support their unabated growth. However, the identity and regulation of the transporter(s) that capture glutamine in MYCN-amplified neuroblastoma cells and the clinical significance of the transporter(s) in neuroblastoma diagnosis remain largely unknown. Here, we performed a systemic glutamine influx analysis and identified that MYCN-amplified neuroblastoma cells predominantly rely on activation of ASCT2 (solute carrier family 1 member 5, SLC1A5) to maintain sufficient levels of glutamine essential for the TCA cycle anaplerosis. Consequently, ASCT2 depletion profoundly inhibited glutaminolysis, concomitant with a substantial decrease in cell proliferation and viability in vitro and inhibition of tumourigenesis in vivo. Mechanistically, we identified ATF4 as a novel regulator which coordinates with N-Myc to directly activate ASCT2 expression. Of note, ASCT2 expression, which correlates with that of N-Myc and ATF4, is markedly elevated in high-stage neuroblastoma tumour samples compared with low-stage ones. More importantly, high ASCT2 expression is significantly associated with poor prognosis and survival of neuroblastoma patients. In aggregate, these findings elucidate a novel mechanism depicting how cell autonomous insults (MYCN amplification) and microenvironmental stresses (ATF4 induction) in concert coordinate ASCT2 activation to promote aggressive neuroblastoma progression, and establish ASCT2 as a novel biomarker in patient prognosis and stratification.

MicroRNA-92a (miR-92a) has been reported to play important roles in tumorigenesis of human various cancers. However, the roles and underlying molecular mechanism of miR-92a in non-small cell lung cancer (NSCLC) have not been totally elucidated. Therefore, the aims of this study were to determine the role of miR-92a and to elucidate its regulatory mechanism in NSCLC. We found that miR-92a was significantly upregulated in NSCLC tissues compared to matched adjacent normal lung tissues, and its expression is significantly associated with clinical characteristics of patients, including tumor, node, and metastasis (TNM) stage; tumor size; and lymph node metastasis (all P < 0.01). Function assays demonstrated that upregulation of miR-92a in NSCLC cells promoted cell proliferation, migration, and invasion, decreased apoptosis and caspase-3 activity, and enhanced chemoresistance of NSCLC cells, whereas downregulation of miR-92a showed the opposite effects. Moreover, phosphatase and tensin homolog (PTEN), a unique tumor suppressor gene, was confirmed as a direct target of miR-92a, and PTEN messenger RNA (mRNA) expression was decreased in NSCLC tissues and was inversely correlated with miR-92a. Downregulation of PTEN could mimic the same effects of miR-92a mimic in NSCLC cells and rescue the effects on NSCLC cells induced by miR-92a inhibitor. Taken together, these findings suggested that miR-92a could promote growth, metastasis, and chemoresistance in NSCLC cells at least partially by targeting PTEN.

Deamidation of glutamine to glutamate by glutaminase 1 (GLS1, also called GLS) and GLS2 is an essential step in both glutaminolysis and glutathione (GSH) biosynthesis. However, mechanisms whereby cancer cells regulate glutamine catabolism remains largely unknown. We report here that N-Myc, an essential Myc family member, promotes conversion of glutamine to glutamate in MYCN-amplified neuroblastoma cells by directly activating GLS2, but not GLS1, transcription. Abrogation of GLS2 function profoundly inhibited glutaminolysis, which resulted in feedback inhibition of aerobic glycolysis likely due to thioredoxin-interacting protein (TXNIP) activation, dramatically decreasing cell proliferation and survival in vitro and in vivo. Moreover, elevated GLS2 expression is significantly elevated in MYCN-amplified neuroblastomas in comparison with non-amplified ones, correlating with unfavorable patient survival. In aggregate, these results reveal a novel mechanism deciphering context-dependent regulation of metabolic heterogeneities, uncovering a previously unsuspected link between Myc, GLS2 and tumor metabolism.

The purpose of the present study was to detect the expression levels of circulating miR-148a in the peripheral blood of osteosarcoma patients and to further investigate the clinicopathological, diagnostic, and prognostic value of miR-148a. Eighty-nine patients with initially diagnosed osteosarcoma who successfully underwent surgical resection were enrolled in this prospective study. The expression levels of circulating miR-148a were detected by real-time quantitative RT-PCR. All statistical analyses were performed with SPSS 18.0 statistical software to determine the potential values of circulating miR-148a on the clinicopathological factors, diagnosis, and prognosis. The expression levels of circulating miR-148a in osteosarcoma patients were significantly higher than that in the healthy controls (P < 0.001), and miR-148a was capable of distinguishing osteosarcoma patients from healthy controls effectively (AUC = 0.783). In addition, miR-148a expression was significantly associated with tumor size (P = 0.049) and distant metastasis (P = 0.004). Univariate survival analysis demonstrated that patients with miR-148a high expression had significantly poor overall survival (P < 0.001) and disease-specific survival (P < 0.001) after 5 years' operation. Multivariate survival analysis confirmed that miR-148a high expression was an independent predictor for unfavorable overall survival (P = 0.003) and disease-specific survival (P = 0.008), respectively. Our findings demonstrated that detection of circulating miR-148a expression in the peripheral blood have clinical potentials as an indicator of progressive phenotype, a novel diagnostic biomarker and a promising predictor to identify individuals with poor prognosis for osteosarcoma patients.