Low expression of ITIH5 in adenocarcinoma of the lung is associated with unfavorable patients' outcome

Inter-α-trypsin inhibitor heavy chain 5 (ITIH5) is supposed to be involved in extracellular matrix stability and thus may play a key role in the inhibition of tumor progression. The current study is the first to analyze in depth ITIH5 expression and DNA methylation, as well as its potential clinical impact in non-small-cell lung carcinoma (NSCLC). We examined <i>ITIH5</i> mRNA expression in tumor and adjacent normal lung tissue specimens of NSCLC patients. In addition, methylation frequency of the <i>ITIH5</i> promoter was investigated using methylation-specific PCR and pyrosequencing. Significance of our data was validated by independent data sets from The Cancer Genome Atlas and the Kaplan-Meier Plotter platform. Furthermore, ITIH5 protein expression was evaluated by immunohistochemistry utilizing a tissue microarray with 385 distinct lung tissue samples. Based on our tissue collections, <i>ITIH5</i> mRNA expression was significantly decreased in NSCLC compared to normal lung tissue in line with an increased methylation frequency in lung cancer tissue. Independent TCGA data confirmed significant expression loss of <i>ITIH5</i> in lung cancer concordant with <i>ITIH5</i> promoter hypermethylation in NSCLC. Of interest, low <i>ITIH5</i> mRNA expression was particularly found in the magnoid and squamoid ADC expression subtype, concordant with an unfavorable patients' outcome in squamoid as well as tobacco smoking ADC patients. In conclusion, <i>ITIH5</i> may be a novel putative tumor suppressor gene in NSCLC with a potential molecular significance in the squamoid ADC subtype and further clinical impact for risk stratification of adenocarcinoma patients. In addition, <i>ITIH5</i> may serve as a novel biomarker for prognosis of tobacco smoking ADC patients.