Prognostic significance and biological function of Lamina-associated polypeptide 2 in non-small-cell lung cancer

Abstract

Purpose: Lamina-associated polypeptide 2 (LAP2; encoded by TMPO), is a nuclear protein that may affect chromatin regulation and gene expression through dynamically binding to nuclear lamin. TMPO (LAP2) plays dual roles of either suppressing or promoting proliferation of cells, depending on the status of the cell. It has been reported that TMPO is up-regulated in various cancer types. However, its function in lung cancer has not been studied yet. Materials and methods: A series of clinical microarray datasets for lung cancer were investigated to demonstrate the expression of TMPO. The transcription of TMPO gene in human lung cancer was analyzed using Oncomine platform (www.oncomine.org) according to the standardized procedures described previously. Four separate datasets (Hou Lung, Okayama Lung, Beer Lung, and Garber Lung) were analyzed. Results: Here, we show that TMPO is over-expressed in lung cancer tissues, and that a high level of TMPO indicates a poor prognosis in lung cancer patients. Knockdown of TMPO in lung cancer cells inhibits cell proliferation and induces apoptosis. Also, down-regulation of TMPO leads to an impaired metastatic ability of tumor cells. A nude mice tumor model show that knockdown of TMPO suppresses tumor formation in vivo. Conclusion: Collectively, this study suggests TMPO as an oncogene and a novel prognostic gene in lung cancer.

Keywords: LAP2; TMPO; non-small-cell lung cancer; oncogene; prognostic factor.

Figure 1

TMPO is upregulated in non-small cell lung cancers. The expression of TMPO was assessed in non-small cell lung cancers using Oncomine database. (A) In Hou Lung dataset, TMPO is overexpressed in large cell lung carcinoma, lung adenocarcinoma, and squamous cell lung carcinoma, than in normal tissue. (B–D) TMPO is also significantly upregulated in Okayama Lung (B), Beer Lung (C), and Garber Lung (D) datasets. Analyzed sample numbers are shown under each category. The p-value was calculated using two-tailed and unpaired Student’s t-test, and shown above each graph.

Figure 2

TMPO expression is prognostically relevant in lung cancer patients. (A–E) High expression of TMPO correlates with poor overall survival rates in GSE11969, GSE13213, GSE17710, GSE30219, and GSE37745 datasets from PROG–gene database. (F–H) High expression of TMPO correlates with poor relapse survival in GSE17710 and GSE31210 datasets although not in GSE37745 dataset from PROGgene database. Survival curves were compared using log-rank test.

Figure 3

Expression of TMPO in lung cancer cells. Lung cancer cells were subjected to Western blot analysis for protein expression of TMPO.

Figure 4

Knockdown of TMPO inhibited cell growth and induced cell cycle arrest and apoptosis. (A) H1299 cells were transducted with control vector or shTMPO through lentiviral vector. GFP expression indicated sufficient infection rate of more than 90%. (B) H1299 cells were subjected to Western blotting analysis for TMPO expression. (C) Knockdown of TMPO induced expression alteration of cell cycle and apoptotic regulators. (D) Knockdown of TMPO suppresses proliferation of H1299 lung cancer cells (**p<0.0001). (E) Knockdown of TMPO induces apoptosis in H1299 lung cancer cells (**p<0.0001). (F) Knockdown of TMPO results in G2/M arrest (**p<0.0001).

Figure 5

Knockdown of TMPO expression inhibits the migration and invasion ability of H1299 cells. (A and B) Downregulation of TMPO inhibits the migration ability of H1299 cells by wound healing assay (***p<0.0001). (C and D) Downregulation of TMPO suppresses the invasion ability of H1299 cells by transwell assay (***p<0.0001). (E) Western blot analysis of EMT marker upon TMPO knockdown.

Figure 6

TMPO knockdown inhibits tumor growth in vivo. (A) Tumor growth curve shows that TMPO knockdown suppresses tumor growth in a xenograft nude mice model (p=0.0463). (B) Final tumor weights were measured after mice were sacrificed. Down-regulated TMPO suppressed tumor growth (p=0.0441).