Role of nicotinamide N-methyltransferase in non-small cell lung cancer: in vitro effect of shRNA-mediated gene silencing on tumourigenicity

Abstract

Lung cancer is the second most commonly diagnosed neoplasm, and represents the leading cause of tumour death worldwide. As patients are often diagnosed at a late stage, current therapeutic strategies have limited effectiveness and the prognosis remains poor. Successful treatment depends on early diagnosis and knowledge concerning molecular mechanisms underlying lung carcinogenesis. In the present study, we focused on nicotinamide N-methyltransferase (NNMT), which is overexpressed in several malignancies. First, we analysed NNMT expression in a cohort of 36 patients with non-small cell lung cancer (NSCLC) by immunohistochemistry. Subsequently, we examined NNMT expression levels in the human lung cancer cell line A549 by Real-Time PCR, Western blot and catalytic activity assay, and evaluated the effect of NNMT knockdown on cell proliferation and anchorage-independent cell growth by MTT and soft agar colony formation assays, respectively. NSCLC displayed higher NNMT expression levels compared to both tumour-adjacent and surrounding tissue. Moreover, shRNA-mediated gene silencing of NNMT led to a significant inhibition of cell proliferation and colony formation ability on soft agar. Our results show that the downregulation of NNMT significantly reduced in vitro tumorigenicity of A549 cells and suggest that NNMT could represent an interesting molecular target for lung cancer therapy.

NNMT Silencing Activates Tumor Suppressor PP2A, Inactivates Oncogenic STKs, and Inhibits Tumor Forming Ability

“…The downregulation or silencing of NNMT expression has been shown to increase the sensitivity of carcinoma cells to radiation therapy and decrease tumorigenicity, providing key support for the role of NNMT in promoting treatment resistance and tumorigenesis in cancer cells (17, 35, 36). Existing literature reports the underlying mechanism for NNMT’s role in resistance due to alterations at the epigenetic level, including histones.…”

Identification and Characterization of Cancer Stem Cells from Head and Neck Squamous Cell Carcinoma Cell Lines

“…Although several cancers have been associated with abnormal NNMT expression, its role in cancer cell metabolism remains largely unknown. We previously demonstrated that downregulation of NNMT expression in human oral and lung cancer cell lines significantly inhibited cell growth and tumorigenicity, suggesting that NNMT could play a critical role in the proliferation and tumorigenic capacity of cancer cells, and the possibility of NNMT as a therapeutic target for the treatment of tumor [62][63][64]. In this work, since CSCs appear to be responsible for tumor initiation and progression (for tumor onset, self-renewal/ maintenance, and metastasis), we decided to analyze the mRNA expression and catalytic activity of NNMT in CSCs enriched populations.…”

Nicotinamide N‐methyltransferase in nonmelanoma skin cancers

“…Our studies carried out on cell cultures explored the enzyme involvement in proliferative capacity of tumour cell. shRNA‐mediated NNMT downregulation was associated with a significant decrease of in vitro cell proliferation as well as of anchorage‐independent cell growth in HeLa‐derived KB cancer cell line and in A549 NSCLC cells . In addition, NNMT silencing efficiently reduced in vivo cell growth and tumour formation ability of PE/CA PJ‐15 OSCC cell line .…”

“…shRNA-mediated NNMT downregulation was associated with a significant decrease of in vitro cell proliferation as well as of anchorage-independent cell growth in HeLa-derived KB cancer cell line 22 and in A549 NSCLC cells. 23 In addition, NNMT silencing efficiently reduced in vivo cell growth and tumour formation ability of PE/CA PJ-15 OSCC cell line. 24 On the contrary, the induction of enzyme overexpression in HSC-2 oral cancer cells significantly enhanced in vitro cell proliferation.…”