Co-expression of MDM2 and CDK4 in transformed human mesenchymal stem cells causes high-grade sarcoma with a dedifferentiated liposarcoma-like morphology.

Amplification and overexpression of MDM2 and CDK4 are well-known diagnostic criteria for well-differentiated liposarcoma (WDLPS)/dedifferentiated liposarcoma (DDLPS). Although it was reported that the depletion of MDM2 or CDK4 decreased proliferation in DDLPS cell lines, whether MDM2 and CDK4 induce WDLPS/DDLPS tumorigenesis remains unclear. We examined whether MDM2 and/or CDK4 cause WDLPS/DDLPS, using two types of transformed human bone marrow stem cells (BMSCs), 2H and 5H, with five oncogenic hits (overexpression of hTERT, TP53 degradation, RB inactivation, c-MYC stabilization, and overexpression of HRASv12). In vitro functional experiments revealed that the co-overexpression of MDM2 and CDK4 plays a key role in tumorigenesis by increasing cell growth and migration and inhibiting adipogenic differentiation potency when compared with the sole expression of MDM2 or CDK4. Using mouse xenograft models, we found that the co-overexpression of MDM2 and CDK4 in 5H cells with five additional oncogenic mutations can cause proliferative sarcoma with a DDLPS-like morphology in vivo. Our results suggest that the co-overexpression of MDM2 and CDK4, along with multiple genetic factors, increases the tendency for high-grade sarcoma with a DDLPS-like morphology in transformed human BMSCs by accelerating their growth and migration and blocking their adipogenic potential.

Adipogenesis induces growth inhibition of dedifferentiated liposarcoma.

Well-differentiated liposarcoma (WDLPS) and dedifferentiated liposarcoma (DDLPS) are the most common types of liposarcoma. Although WDLPS and DDLPS patients receive intensive treatment including radical surgery and systemic therapy, their overall 5-year survival rates are 90% and 30%, respectively, indicating that DDLPS is clinically more aggressive. We examined whether adipogenic stimulation induces adipogenesis in human WDLPS/DDLPS cells by using dexamethasone, indomethacin, insulin, and 3-isobutyl-1-methylxanthine (IBMX), all putative medications or drugs. Functional in vitro experiments showed that treatment with these four compounds induced adipogenic potency by transcriptional and translational upregulation of genes related to the maintenance of stemness and adipogenic differentiation. Using in vivo xenograft models, we found that the induction of stemness and adipogenesis inhibited the tumorigenic potency of DDLPS. This study suggests a potential application of drug repositioning in which adipogenesis-inducing compounds could be used to treat DDLPS patients in a clinical setting.

Molecular changes in solitary fibrous tumor progression.

Solitary fibrous tumors (SFTs) are NAB2-STAT6 fusion-associated neoplasms. There are several subtypes of NAB2-STAT6 fusions, but their clinical significances are still unclear. Moreover, the mechanisms of malignant progression are also poorly understood. In this study, using 91 SFT cases, we examined whether fusion variants are associated with clinicopathological parameters and also investigated the molecular mechanism of malignant transformation using whole-exome sequencing. We detected variant 1b (NAB2ex4-STAT6ex2) in 51/91 (56%) cases and variants 2a/2b (NAB2ex6-STAT6ex16/17) in 17/91 (19%) cases. The NAB2-STAT6 fusion variant types were significantly associated with their primary site (P < 0.001). In addition, a TERT promoter mutation was detected in 7/73 (10%) cases, and it showed a significant association with malignant SFTs (P = 0.003). To identify molecular changes during malignant progression, we selected an index patient to obtain parallel tissue samples from the primary and metastatic tumors. In the metastatic tissue, 10 unique molecular alterations, including those in TP53 and APAF1, were detected. In vitro functional experiments showed that APAF1 depletion increased the tumor potency of cells expressing NAB2-STAT6 fusion protein under treatment with staurosporine. We found that TP53 immunopositivity (P = 0.006) and loss of APAF1 immunoreactivity (P < 0.001) were significantly associated with malignant SFTs. Our study suggests that dysfunction of TP53 and APAF1 leads to impaired apoptotic function, and eventually contributes toward malignant SFT transformation. KEY MESSAGES: We firstly found that the TERT promoter mutation was strongly associated with malignant SFTs (P = 0.003) and the representative 1b (NAB2ex4-STAT6ex2) or 2a (NAB2ex6-STAT6ex16) fusion variants similarly contribute to tumorigenicity. We also found that TP53 immunopositivity (P = 0.006) and loss of APAF1 immunoreactivity (P < 0.001) were significantly associated with malignant SFTs. Our study suggests that dysfunction of TP53 and APAF1 leads to impaired apoptotic function, and eventually contributes toward malignant SFT transformation.

MET Exon 14 Skipping Mutations in Lung Adenocarcinoma: Clinicopathologic Implications and Prognostic Values.

INTRODUCTION: Response to mesenchymal-epithelial transition (MET) inhibitors in NSCLC with mesenchymal-epithelial transition gene (MET) exon 14 skipping (METex14) has fueled molecular screening efforts and the search for optimal therapies. However, further work is needed to refine the clinicopathologic and prognostic implications of METex14 skipping. METHODS: Among 795 East Asian patients who underwent a surgical procedure for NSCLC, we screened 45 patients with quintuple-negative (EGFR-negative/KRAS-negative/anaplastic lymphoma kinase gene [ALK]-negative/ROS1-negative/ret proto-oncogene [RET]-negative) lung adenocarcinomas by using reverse-transcriptase polymerase chain reaction and found 17 patients (37.8%) with METex14 skipping. We also investigated the effect of small interfering RNA (siRNA) targeting skipping junction in cells with METex14 skipping. RESULTS: The median age of the 17 patients was 73 years. The acinar subtype was predominant (52.9%), followed by the solid subtype (35.3%). MET immunohistochemistry demonstrated 100% sensitivity and 70.4% specificity. Multivariate analyses showed that patients with METex14 skipping had a higher recurrence rate than those with ALK fusion (versus METex14 skipping) (hazard ratio = 0.283, 95% confidence interval: 0.119-0.670) in stage I to IIIA disease; however, the differences in overall survival were not significant after adjustment for pathologic stage (p = 0.669). Meanwhile, siRNA decreased MET-driven signaling pathways in Hs746T cells, and combined treatment with siRNA and crizotinib inhibited cell proliferation in crizotinib-resistant H596 cells. CONCLUSIONS: The prevalence of METex14 skipping was quite high in East Asian patients without other driver mutations in lung adenocarcinomas. METex14 skipping was associated with old age, the acinar or solid histologic subtype, and high MET immunohistochemical expression. The prognosis of patients with METex14 skipping was similar to that of patients with major driver mutations. siRNA targeting the junction of METex14 skipping could inhibit MET-driven signaling pathways in cells with METex14 skipping.