Oncogenic Ras‐mediated downregulation of Clast1/LR8 is involved in Ras‐mediated neoplastic transformation and tumorigenesis in NIH3T3 cells

Abstract

Oncogenic Ras proteins transform cells by way of multiple downstream signaling pathways that promote the genesis of human cancers. However, the exact cellular mechanisms by which downstream targets are regulated are not fully understood. Here, we show that oncogenic Ras reduced Clast1/LR8 transcript levels in mouse NIH3T3 fibroblasts and human WI38 fibroblasts. Clast1/LR8 transcript was undetectable in H460, A549, and H1299 cells showing high Ras activity, but was relatively abundant in DMS53 cells displaying low Ras activity. We also showed that K-Ras siRNA restored Clast1/LR8 expression in H460 and A549 cells, and that inhibitors of DNA methylation and histone deacetylation reversed oncogenic H-Ras-mediated suppression of Clast1/LR8 transcription. Additionally, ectopic expression of Clast1/LR8 inhibited serum-stimulated phosphorylation of ERK1/2 and Akt in H-RasV12-transformed NIH3T3 cells. We further showed that the expression of Clast1/LR8 interfered with oncogenic Ras-induced NIH3T3 cell transformation and invasion. Finally, our results showed that Clast1/LR8 inhibited Ras-induced proliferation of, and tumor formation by, oncogenic H-RasV12-transformed NIH3T3 cells in vivo. This study identifies the downregulation of Clast1/LR8 as a potentially important mechanism by which oncogenic Ras-

Abnormal accumulation of human transmembrane (TMEM)-176A and 176B proteins is associated with cancer pathology

“…The recent reports implicating TMEM176A or TMEM176B in human cancer were primarily based on data that show abnormal mRNA transcript levels for TMEM176A and/or 176B (Wang et al, 2002; Hodo et al, 2010; Ryu et al, 2010; Strelnikov et al, 2010; Gottschling et al, 2012). One caveat about these findings is that mRNA levels do not always positively correlate with protein levels in cells or tissues due to variables such as mRNA stability, translational regulation, or proteolysis.…”

“…A study using serial analysis of gene expression showed that both 5′ and 3′ intronic transcripts encoding the human TMEM176B gene are significantly reduced in HCC tissues (Hodo et al, 2010). It has been proposed that the oncogenic Ras protein reduces mouse TMEM176B transcription in response to hypermethylation and histone deacetylation (Ryu et al, 2010). Despite the apparent correlation between transcript levels and tumorigenesis, to date no direct evidence has been established regarding abnormal protein levels of human TMEM176A or 176B and cancer pathology.…”

Identification of novel targets for antiangiogenic therapy by comparing the gene expressions of tumor and normal endothelial cells

“…(45,46) It was discovered in human lung fibroblasts and is associated with human small cell lung carcinoma. (47) Although several recent reports implicate human TMEM176B in cancer, (48)(49)(50) no direct evidence is available regarding its function in cancer pathogenesis, including tumor angiogenesis. Here, we report for the first time overexpression of TMEM176B in TEC and further show using RNAi that TMEM176B mediates TEC migration.…”

RORγt+ cells selectively express redundant cation channels linked to the Golgi apparatus

“…Importantly, Tmem176b has a co-regulated homologue, namely Tmem176a , located within the same genomic locus and likely resulting from a recent duplication 11 12 14 . It is important to note that the co-expression of these two structurally similar genes is not restricted to myeloid cells but extends to other cell types including non-hematopoietic cells 15 16 17 18 , thus strongly suggesting other intracellular functions beyond antigen cross-presentation.…”