Abstract
BackgroundWe tried to elaborate the molecular mechanism of ETS-like transcription factor 4 (ELK4) affecting gastric cancer (GC) progression through M2 polarization of macrophages mediated by lysine-specific demethylase 5A (KDM5A)-Praja2 (PJA2)-kinase suppressor of ras 1 (KSR1) axis.MethodsGC expression dataset was obtained from GEO database, and the downstream regulatory mechanism of ELK4 was predicted. Tumor-associated macrophages (TAMs) were isolated from GC tissues. The interaction among ELK4, KDM5A, PJA2 and KSR1 was analyzed by dual luciferase reporter gene, ChIP and Co-IP assays. The stability of KSR1 protein was detected by cycloheximide (CHX) treatment. After TAMs were co-cultured with HGC-27 cells, HGC-27 cell biological processes were assessed through gain- and loss-of function assays. Tumorigenicity was detected by tumorigenicity test in nude mice.ResultsIn GC and TAMs, ELK4, KDM5A and KSR1 were highly expressed, while PJA2 was lowly expressed. M2 polarization of macrophages promoted the development of GC. ELK4 activated KDM5A by transcription and promoted macrophage M2 polarization. KDM5A inhibited the expression of PJA2 by removing H3K4me3 of PJA2 promoter, which promoted M2 polarization of macrophages. PJA2 reduced KSR1 by ubiquitination. ELK4 promoted the proliferative, migrative and invasive potentials of GC cells as well as the growth of GC xenografts by regulating KSR1.ConclusionELK4 may reduce the PJA2-dependent inhibition of KSR1 by transcriptional activation of KDM5A to promote M2 polarization of macrophages, thus promoting the development of GC.
Highlights
We tried to elaborate the molecular mechanism of ETS-like transcription factor 4 (ELK4) affecting gastric cancer (GC) progression through M2 polarization of macrophages mediated by lysine-specific demethylase 5A (KDM5A)-Praja2 (PJA2)-kinase suppressor of ras 1 (KSR1) axis
The results showed that the mRNA expression levels of M1 markers: IL-1β, TNF and NOS2 in GC tissues were decreased, while the mRNA expression levels of M2 markers: Fizz1, Ym1 and Arg-1 were increased (Fig. 1A), indicating that macrophages mainly polarized to M2 type in GC tissues
The results showed that ELK4 was upregulated in GC tissues and Tumor-associated macrophages (TAMs) and mainly expressed in GC-TAMs
Summary
We tried to elaborate the molecular mechanism of ETS-like transcription factor 4 (ELK4) affecting gastric cancer (GC) progression through M2 polarization of macrophages mediated by lysine-specific demethylase 5A (KDM5A)-Praja (PJA2)-kinase suppressor of ras 1 (KSR1) axis. Lysine-specific demethylase 5A (KDM5A/RBP2) is identified as a chromatin-modifying enzyme related to transcriptional regulation by catalyzing removal of methyl groups from methylated lysine 4 of histone H3 and this gene is observed in multiple cancers including GC [8]. PJA2 has been identified as the E3 ligase which can ubiquitylate kinase suppressor of ras 1 (KSR1) [13], a molecular scaffold of the Raf/MEK/extracellular signal-regulated kinase (ERK) cascade which can augment oncogenic Ras signaling [14]. Considering all the above findings, we propose a hypothesis in the current study that ELK4 may affect the development of GC by regulating macrophages, with the involvement of the KDM5A-PJA2-KSR1 axis
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