IMP3Expression Relevant With Prognosis And The Underlying Mechanism Involved In Lung Adenocarcinoma

Lung cancer is the leading cause of cancer mortality with the highest incidence all over the world, and the incidence rate still increases year by year. Recently in the third inquiry about cause of death in China announced by Ministry of Public Health, lung cancer took the first place of the mortality caused by tumor. Histopathologically, lung cancer is divided into small cell lung carcinoma(SCLC) and non-small cell lung carcinoma(NSCLC). NSCLC mainly includes squamous cell carcinoma(SCC), adenocarcinoma(ADC) and large cell carcinoma(LCC). In the recent year, the most common histologic type of NSCLC is ADC, accounting for nearly half of all lung cancers. ADC is less accurately diagnosed due to the histological complexity, so it is in badly need of realizing the underlying pathogenesis. In this study, first we discussed the prognostic significance of the new IASLC/ATS/ERS classification of ADC, which divided the invasive ADC into five subtypes. Then the correlation of IMP3expression and prognosis, and the underlying functional mechanism were further investigated. The whole study is comprised of the following three parts.Part Ⅰ The relationship between new IASLC/ATS/ERS classification and lung adenocarcinomaObjective:The new IASLC/ATS/ERS international multidisciplinary classification of lung adenocarcinoma makes a lot of change, and the pathological and clinical significance remains to be proved. In this study, we discussed the correlation between subtypes of invasive lung adenocarcinoma and clinical significance in order to find the evidence to support the new classification.Materials and methods:The clinical data of196patients with invasive lung adenocarcinoma was collected. We rechecked the H&E slides to classify them with the new IASLC/ATS/ERS classification, and analyzed the relationship of new histological subtypes and the clinicopathological parameters. Then96cases with follow-up data for more than18months were gathered to investigate the relevance between subtypes and prognosis. Results:There were statistical differences among the five histological subtypes in pathological differentiation (P＜0.0001), lymphatic metastasis (P=0.015), T staging (P=0.004) and pTNM stage (P=0.001). Pairwise comparison showed the lepidic subtype was statistically different from the other subtypes, which revealed lepidic subtype was relevant to early pTNM stage, well differentiation and metastasis-free status of lymph nodes. The survival analysis showed the patients with solid subtype seemed to have shorter disease-free survival and overall survival time compared with the non-solid subtypes. Multivariate COX regression revealed the solid subtype could be a prognostically independent factor of lung adenocarcinoma, the hazard ratio of which was1.220(95%CI,1.053～1.414; P=0.008) in disease-free survival and1.224(95%CI,1.011～1.482; P=0.038) in overall survival.Conclusion:Statistical differences of clinicopathological characteristics and prognosis are discovered among five histological subtypes of lung adenocarcinoma. The solid subtype can be one of the prognostically independent factors, which backs up the clinical significance of the new subtype classification.Part II The correlation between IMP3expression and lung adenocarcinomaObjective:Overexpression of IMP3has been confirmed in many kinds of malignant tumors, which was relevant to high histological grade, lymphatic metastasis and poor prognosis. But only a few studies have examined IMP3expression in lung adenocarcinoma. In this part, we examined IMP3expression in cases of lung adenocarcinoma, and analyzed its correlation with clinicopathological parameters and prognosis to provide some new idea for further research.Materials and methods:IMP3expression was examined in the same cases in Part I by immunohistological methods, and then we divided the cases into IMP3high-expression (moderately/strongly positive) group and IMP3low-expression (negative/mildly positive) group by staining results. Analysis was stratified by clinicopathological parameters and prognosis, including the new IASLC/ATS/ERS classification mentioned above.Results:There were statistical differences in pathological differentiation, new subtype classification, pTNM stage and lymphatic metastasis (P＜0.0001) between high-expression and low-expression groups, while no statistical significance in age, gender and T staging. Univariate survival analysis revealed the correlation between high expression of IMP3and poor prognosis (P<0.05), but there was no sufficient evidence to support IMP3as a prognostically independent factor yet.Conclusion:High expression of IMP3usually appears with the condition of poor differentiation, solid subtype, advanced pTNM stage and lymphatic metastasis, which implies IMP3as an invasive ability inducer in lung adenocarcinoma. Survival analysis showed relevance between IMP3expression and clinical prognosis, but there was no more evidence to prove it prognostically independent. As a result, IMP3may act as a prognostic factor combined with others, such as pTNM stage and lymphatic metastasis status.Part Ⅲ The underlying mechanism of IMP3inducing invasive ability in lung adenocarcinomaObjective:Part II had revealed the relevance between high expression of IMP3and increasing invasive ability in lung adenocarcinoma, but the functional mechanism still remained unclear. This part emphasized on the effect of IMP3in tumor cell migration and the relationship of IMP3and EMT (epithelial-mesenchymal transition) to make a preliminary study on the underlying biological mechanism.Materials and methods:We examined IMP3expression in several cell lines, and then transfected IMP3high-expression cell line with siRNA, while low-expression cell line with overexpression plasmid vector. We detected the ability of cell migration by cell scratch tests in transfection group and control group. In addition, the expression changes of E-cadherin, N-cadherin and Vimentin were detected by Western blot.Results:Low expression of E-cadherin and high expression of N-cadherin and Vimentin were detected in IMP3high-expression cell line, while the opposite result was found in IMP3low-expression cell line. Interference of IMP3expression was related with increased expression level of E-cadherin and decreased level of N-cadherin and Vimentin, while overexpression of IMP3expression was relevant with decreased expression level of E-cadherin and increased level of N-cadherin and Vimentin. The increased IMP3expression level promoted cell migration in cell scratch tests.Conclusion:The change trend of IMP3expression level is consistent with N-cadherin and Vimentin, and opposite to E-cadherin. IMP3may promote invasive ability of tumor cell through EMT in lung adenocarcinoma. Since the carcinogenesis and development of lung adenocarcinoma is determined by multiple factors, interaction of IMP3with other genes and the related molecular pathways need to be further investigated.