Deregulated expression of hnRNP A/B proteins in human non-small cell lung cancer: parallel assessment of protein and mRNA levels in paired tumour/non-tumour tissues

Georgios Boukakis,Meropi Patrinou-Georgoula,Apostolia Guialis,Christos Valavanis,Maria Lekarakou

doi:10.1186/1471-2407-10-434

Georgios Boukakis, Meropi Patrinou-Georgoula + Show 3 more

Open Access

https://doi.org/10.1186/1471-2407-10-434

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Abstract

BackgroundHeterogeneous nuclear ribonucleoproteins (hnRNPs) of the A/B type (hnRNP A1, A2/B1, A3) are highly related multifunctional proteins participating in alternative splicing by antagonising other splicing factors, notably ASF/SF2. The altered expression pattern of hnRNP A2/B1 and/or splicing variant B1 alone in human lung cancer and their potential to serve as molecular markers for early diagnosis remain issues of intense investigation. The main objective of the present study was to use paired tumour/non-tumour biopsies from patients with non-small cell lung cancer (NSCLC) to investigate the expression profiles of hnRNP A1, A2/B1 and A3 in conjunction with ASF/SF2.MethodsWe combined western blotting of tissue homogenates with immunohistochemical examination of fixed tissue sections and quantification of mRNA expression levels in tumour versus adjacent normal-looking areas of the lung in the same patient.ResultsOur study, in addition to clear evidence of mostly uncoupled deregulation of hnRNPs A/B, has revealed hnRNP A1 to be the most deregulated protein with a high frequency of over-expression (76%), followed by A3 (52%) and A2/B1 (43%). Moreover, direct comparison of protein/mRNA levels showed a lack of correlation in the case of hnRNP A1 (as well as of ASF/SF2), but not of A2/B1, suggesting that different mechanisms underlie their deregulation.ConclusionOur results provide strong evidence for the up-regulation of hnRNP A/B in NSCLC, and they support the existence of distinct mechanisms responsible for their deregulated expression.

Highlights

Heterogeneous nuclear ribonucleoproteins of the A/B type are highly related multifunctional proteins participating in alternative splicing by antagonising other splicing factors, notably ASF/SF2
Results Heterogeneous nuclear ribonucleoproteins (hnRNPs) protein levels in paired tumour/non-tumour lung tissue specimens from patients with nonsmall cell lung cancer (NSCLC) This study included 21 patients who had been operated on for non-small cell lung cancer (NSCLC)
We focused our study on the major hnRNP A/B type proteins that include, in addition to the hnRNP A2/B1 currently implicated mostly in lung cancer, the hnRNP A1 and A3 protein species

Summary

Introduction

Heterogeneous nuclear ribonucleoproteins (hnRNPs) of the A/B type (hnRNP A1, A2/B1, A3) are highly related multifunctional proteins participating in alternative splicing by antagonising other splicing factors, notably ASF/SF2. HnRNP A2/B1 refers to two isoforms; the major hnRNP A2 and the minor B1 form that results from the inclusion of an extra exon of 12 amino acid residues [9] Their proportions, both in protein and mRNA levels, vary in different cells and tissues, with B1 constituting roughly 2-5% of A2 [10,11]. The major nuclear function of hnRNPs is thought to be in splicing and in alternative splicing This is especially the case for hnRNP A1 and A2/B1, which have been shown to antagonise, in a concentration dependent manner, protein members of the SR group, notably ASF/SF2, and to influence the mode of splicing of mRNA target molecules [12]. Changes in the expression levels of hnRNP A/B and ASF/SF2 have been reported in human colon adenocarcinomas [13] and in a mouse model of lung carcinogenesis [14]

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