Enhanced MAPK signaling drives ETS1-mediated induction of miR-29b leading to downregulation of TET1 and changes in epigenetic modifications in a subset of lung SCC

Abstract

Non-small-cell lung cancer is the leading cause of cancer death worldwide and is comprised of several histological subtypes, the two most common being adenocarcinoma (AC) and squamous cell carcinoma (SCC). Targeted therapies have successfully improved response rates in patients with AC tumors. However, the majority of SCC tumors lack specific targetable mutations, making development of new treatment paradigms for this disease challenging. In the present study, we used iterative non-negative matrix factorization, an unbiased clustering method, on mRNA expression data from the cancer genome atlas (TCGA) and a panel of 24 SCC cell lines to classify three disease segments within SCC. Analysis of gene set enrichment and drug sensitivity identified an immune-evasion subtype that showed increased sensitivity to nuclear factor-κB and mitogen-activated protein kinase (MAPK) inhibition, a replication-stress associated subtype that showed increased sensitivity to ataxia telangiectasia inhibition, and a neuroendocrine-associated subtype that showed increased sensitivity to phosphoinositide 3-kinase and fibroblast growth factor receptor inhibition. Additionally, each of these subtypes exhibited a unique microRNA expression profile. Focusing on the immune-evasion subtype, bioinformatic analysis of microRNA promoters revealed enrichment for binding sites for the MAPK-driven ETS1 transcription factor. Indeed, we found that knockdown of ETS1 led to upregulation of eight microRNAs and downregulation of miR-29b in the immune-evasion subtype. Mechanistically, we found that miR-29b targets the DNA-demethylating enzyme, TET1, for downregulation resulting in decreased 5-hmC epigenetic modifications. Moreover, inhibition of MAPK signaling by gefitinib led to decreased ETS1 and miR-29b expression with a corresponding increase in TET1 expression and increase in 5-hmC. Collectively, our work identifies three subtypes of lung SCC that differ in drug sensitivity and shows a novel mechanism of miR-29b regulation by MAPK-driven ETS1 expression which leads to downstream changes in TET1-mediated epigenetic modifications.

p53-Suppressed Oncogene TET1 Prevents Cellular Aging in Lung Cancer

“…Possible alterations in expression of the TET genes in lung cancer were first suggested by the observation of reduced levels of their enzymatic product 5hmC in tumor versus normal lung tissue (24). That finding was supported by three studies that showed negative correlation between TET1 expression and miR-767, MAPK/miR29b, and EGFR/CEBPa levels across lung tumors of different histology (29)(30)(31)(32). However, none of those studies analyzed TET1 levels in primary lung tumors compared with normal tissue.…”

Significance of microRNAs in Androgen Signaling and Prostate Cancer Progression

“…Importantly, in other studies in breast cancer and myelodysplastic syndrome (MDS), it was suggested that miRNA-mediated TET2 repression contributes to tumorigenesis [ 96 , 97 ]. It was also reported that miR-22 and miR-29 function as onco-miRs by regulating epigenetic status in cancer [ 98 , 99 ]. In addition to these two miRNAs, several androgen-regulated miRNAs such as miR-125b and miR-200a repressed TET2 -3′UTR, suggesting TET2 is a common target of these AR-induced miRNAs [ 91 ].…”

Sulforaphane modulates microRNA expression in colon cancer cells to implicate the regulation of oncogenes CDC25A, HMGA2 and MYC

“…MiR-29b-3p is computationally predicted by miRanda to target the following tumour suppressor genes (TSGs): ADAMTS9, ARRDC3, CASP7, FEM1B, HBP1, HPGD, ING3, NAV3, PTEN, RhoBTBl, SEL1L, SLC5A8, SUV420H2, TET1, TET2 and UVRAG (24). Direct interactions between miR-29b-3p and the 3’-UTRs of colorectal cancer-suppressing TET1 and TET2 have been demonstrated by luciferase assays already (28), (29), (30). Interestingly, a different ITC, phenethyl isothiocyanate, was reported to inhibit the upregulation of miR-29b-3p in mouse lung tissue mediated by environmental cigarette smoke (31).…”