Divergent lncRNA MYMLR regulates MYC by eliciting DNA looping and promoter-enhancer interaction.

Long non-coding RNAs (lncRNAs) function in a wide range of processes by diverse mechanisms, though their roles in regulation of oncogenes and/or tumor suppressors remain rather elusive. We performed a global search for lncRNAs affecting MYC activity using a systems biology-based approach with a K supercomputer and the GIMLET algorism based on local distance correlations. Consequently, MYMLR was identified and experimentally shown to maintain MYC transcriptional activity and cell cycle progression despite the low levels of expression. A proteomic search for MYMLR-binding proteins identified PCBP2, while it was also found that MYMLR places a 557-kb upstream enhancer region in the proximity of the MYC promoter in cooperation with PCBP2. These findings implicate a crucial role for MYMLR in regulation of the archetypical oncogene MYC and warrant future studies regarding the involvement of low copy number lncRNAs in regulation of other crucial oncogenes and tumor suppressor genes.

Alopecia in Harlequin mutant mice is associated with reduced AIF protein levels and expression of retroviral elements.

We investigated the contribution of apoptosis-inducing factor (AIF), a key regulator of mitochondrial biogenesis, in supporting hair growth. We report that pelage abnormalities developed during hair follicle (HF) morphogenesis in Harlequin (Hq) mutant mice. Fragility of the hair cortex was associated with decreased expression of genes encoding structural hair proteins, though key transcriptional regulators of HF development were expressed at normal levels. Notably, Aifm1 (R200 del) knockin males and Aifm1(R200 del)/Hq females showed minor hair defects, despite substantially reduced AIF levels. Furthermore, we cloned the integrated ecotropic provirus of the Aifm1Hq allele. We found that its overexpression in wild-type keratinocyte cell lines led to down-regulation of HF-specific Krt84 and Krtap3-3 genes without altering Aifm1 or epidermal Krt5 expression. Together, our findings imply that pelage paucity in Hq mutant mice is mechanistically linked to severe AIF deficiency and is associated with the expression of retroviral elements that might potentially influence the transcriptional regulation of structural hair proteins.

Thyroid transcription factor-1-regulated microRNA-532-5p targets KRAS and MKL2 oncogenes and induces apoptosis in lung adenocarcinoma cells.

Thyroid transcription factor-1 (TTF-1), also known as NKX2-1, plays a role as a lineage-survival oncogene in lung adenocarcinoma that possesses double-edged sword characteristics. Although evidence from previous studies has steadily accumulated regarding the roles of TTF-1 in transcriptional regulation of protein-coding genes, little is known about its regulatory relationship with microRNAs. Here, we utilized an integrative approach designed to extract maximal information from expression profiles of both patient tumors in vivo and TTF-1-inducible cell lines in vitro, which identified microRNA (miR)-532-5p as a novel transcriptional target of TTF-1. We found that miR-532-5p is directly regulated by TTF-1 through its binding to a genomic region located 8 kb upstream of miR-532-5p, which appears to impose transcriptional regulation independent of that of CLCN5, a protein-coding gene harboring miR-532-5p in its intron 3. Furthermore, our results identified KRAS and MKL2 as novel direct targets of miR-532-5p. Introduction of miR-532-5p mimics markedly induced apoptosis in KRAS-mutant as well as KRAS wild-type lung adenocarcinoma cell lines. Interestingly, miR-532-5p showed effects on MEK-ERK pathway signaling, specifically in cell lines sensitive to siKRAS treatment, whereas those miR-532-5p-mediated effects were clearly rendered as phenocopies by repressing expression or inhibiting the function of MKL2 regardless of KRAS mutation status. In summary, our findings show that miR-532-5p is a novel transcriptional target of TTF-1 that plays a tumor suppressive role by targeting KRAS and MKL2 in lung adenocarcinoma.

CD73 Is Regulated by the EGFR-ERK Signaling Pathway in Non-small Cell Lung Cancer.

BACKGROUND/AIM: Successful therapy of EGFR-mutant NSCLC remains a challenging task despite initial benefits with the usage of EGFR tyrosine kinase inhibitors. Cancer immunotherapy has shown promising results in certain tumors, but response rate in EGFR-mutant NCLC is low, because these tumors are thought to have weak immunogenicity. MATERIALS AND METHODS: We used data from in vivo NSCLC databases as well as from in vitro cell culture experiments to investigate the regulation of CD73 by EGFR. RESULTS: EGFR expression was correlated with CD73 expression in patients' datasets, with EGFR-mutant tumors showing higher expression than their EGFR wildtype counterparts. Treatment of EGFR-mutant NSCLC cell lines with EGFR TKI reduced expression of CD73 at both mRNA and protein level. Among EGFR downstream signaling pathways, the Ras-Raf-ERK pathway was involved in the regulation of CD73 expression directly via ERK1/2 without the engagement of RSKs or MSKs. CONCLUSION: The results of this study may provide novel therapeutic strategies for the treatment of oncogene-driven NSCLC.

Second-line treatment of EGFR T790M-negative non-small cell lung cancer patients.

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) are the currently recommended treatment for advanced EGFR mutation-positive non-small cell lung cancer (NSCLC). Acquired resistance inevitably develops, with the EGFR T790M mutation comprising approximately 55% of the mechanisms of resistance following first- or second-generation EGFR-TKI therapy (e.g. gefitinib, erlotinib, afatinib, and dacomitinib). Patients without T790M are a heterogeneous group for whom platinum-based chemotherapy is currently recommended as a second-line treatment. In addition to secondary mutations in EGFR (e.g. T790M), the currently known resistance mechanisms can be classified into the following three categories: bypass pathways, downstream signaling pathways, and histologic transformations. Given the evolving knowledge and convenience of diagnosing acquired resistance mechanisms by next-generation sequencing and liquid biopsy, exploratory studies targeting these resistance mechanisms and incorporating immunotherapy into the treatment paradigm have become the mainstream of future development. This review focuses on acquired resistance mechanisms other than T790M that develop after first- or second-generation EGFR-TKI therapy. Exploratory second-line treatments targeting resistance mechanisms as well as combination immunotherapy and chemotherapy in ongoing clinical trials are reviewed here. We also highlight the recent development of next-generation sequencing and liquid biopsy in this field.

Alopecia in a viable phospholipase C delta 1 and phospholipase C delta 3 double mutant.

BACKGROUND: Inositol 1,4,5trisphosphate (IP(3)) and diacylglycerol (DAG) are important intracellular signalling molecules in various tissues. They are generated by the phospholipase C family of enzymes, of which phospholipase C delta (PLCD) forms one class. Studies with functional inactivation of Plcd isozyme encoding genes in mice have revealed that loss of both Plcd1 and Plcd3 causes early embryonic death. Inactivation of Plcd1 alone causes loss of hair (alopecia), whereas inactivation of Plcd3 alone has no apparent phenotypic effect. To investigate a possible synergy of Plcd1 and Plcd3 in postnatal mice, novel mutations of these genes compatible with life after birth need to be found. METHODOLOGY/PRINCIPAL FINDINGS: We characterise a novel mouse mutant with a spontaneously arisen mutation in Plcd3 (Plcd3(mNab)) that resulted from the insertion of an intracisternal A particle (IAP) into intron 2 of the Plcd3 gene. This mutation leads to the predominant expression of a truncated PLCD3 protein lacking the N-terminal PH domain. C3H mice that carry one or two mutant Plcd3(mNab) alleles are phenotypically normal. However, the presence of one Plcd3(mNab) allele exacerbates the alopecia caused by the loss of functional Plcd1 in Del(9)olt1Pas mutant mice with respect to the number of hair follicles affected and the body region involved. Mice double homozygous for both the Del(9)olt1Pas and the Plcd3(mNab) mutations survive for several weeks and exhibit total alopecia associated with fragile hair shafts showing altered expression of some structural genes and shortened phases of proliferation in hair follicle matrix cells. CONCLUSIONS/SIGNIFICANCE: The Plcd3(mNab) mutation is a novel hypomorphic mutation of Plcd3. Our investigations suggest that Plcd1 and Plcd3 have synergistic effects on the murine hair follicle in specific regions of the body surface.