Enhanced expression of LINE-1-encoded ORF2 protein in early stages of colon and prostate transformation.

Chiara De Luca,Steno Sentinelli,Corrado Spadafora,Michele Gallucci,Paola Sinibaldi-Vallebona,Ilaria Sciamanna,Andreas Hoffmann,Gerald G Schumann,Fiorella Guadagni

doi:10.18632/oncotarget.6767

Abstract

LINE-1 (L1) retrotransposons are a source of endogenous reverse transcriptase (RT) activity, which is expressed as part of the L1-encoded ORF2 protein (L1-ORF2p). L1 elements are highly expressed in many cancer types, while being silenced in most differentiated somatic tissues. We previously found that RT inhibition reduces cell proliferation and promotes differentiation in neoplastic cells, indicating that high endogenous RT activity promotes cancer growth. Here we investigate the expression of L1-ORF2p in several human types of cancer.We have developed a highly specific monoclonal antibody (mAb chA1-L1) to study ORF2p expression and localization in human cancer cells and tissues.We uncover new evidence for high levels of L1-ORF2p in transformed cell lines and staged epithelial cancer tissues (colon, prostate, lung and breast) while no or only basal ORF2p expression was detected in non-transformed cells. An in-depth analysis of colon and prostate tissues shows ORF2p expression in preneoplastic stages, namely transitional mucosa and prostate intraepithelial neoplasia (PIN), respectively.Our results show that L1-ORF2p is overexpressed in tumor and in preneoplastic colon and prostate tissues; this latter finding suggests that ORF2p could be considered as a potential early diagnostic biomarker.

Highlights

Long Interspersed Element-1 (LINE-1, L1) members belong to the family of autonomous retrotransposable elements, which spread in the human genome via RNA intermediates
We have investigated the function of L1encoded reverse transcriptase (RT) in tumorigenesis using two complementary approaches: in the first one, we inhibited the RT activity pharmacologically in tumor cell lines using efavirenz, a non-nucleoside RT inhibitor used in AIDS therapy [14, 15]; in the second approach, we downregulated the expression of L1-encoded ORF2p by RNA interference (RNAi) [14, 16]
As shown in panel B, the band intensity was significantly reduced when monoclonal antibody (mAb) chA1-L1 was tested on extracts from A-375 cells in which L1 expression was stably downregulated by RNA interference (RNAi), in comparison with non-interfered control cells [16]

Summary

Introduction

Long Interspersed Element-1 (LINE-1, L1) members belong to the family of autonomous retrotransposable elements (or retrotransposons), which spread in the human genome via RNA intermediates. We have investigated the function of L1encoded RT in tumorigenesis using two complementary approaches: in the first one, we inhibited the RT activity pharmacologically in tumor cell lines using efavirenz, a non-nucleoside RT inhibitor used in AIDS therapy [14, 15]; in the second approach, we downregulated the expression of L1-encoded ORF2p by RNA interference (RNAi) [14, 16]. Both approaches consistently reduced proliferation and restored differentiation traits in cancer cells, yielding remarkable changes in cell morphology and in global transcription profiles of both coding and non-coding RNAs [15]; notably, neither approach caused substantial alterations in non-transformed cells

Methods

Results

Conclusion