Characteristics of CD44 alternative splice pattern in the course of human colorectal adenocarcinoma progression

Balázs Bánky,Tamás Barbai,Lívia Rásó-Barnett,József Tímár,Péter Becságh,Erzsébet Rásó

doi:10.1186/1476-4598-11-83

Abstract

BackgroundCD44 is considered as ‘a’ metastasis associated gene, despite the fact that it is an umbrella term for a group of molecules produced from a single gene by alternative splicing. However, little consideration is given to the above in the literature of colorectal carcinomas as well as other tumour types, leading to confusion and contradictory results about its possible role in tumour progression.MethodsWe compared the CD44 alternative splice pattern (ASP) of three genetically different human colorectal cancer cell lines (HT25, HT29, HCT116) using a series of PCR reactions and next- generation sequencing method, as well as identified a colorectal adenocarcinoma specific CD44 ASP. This ASP was further investigated in terms of its qualitative and quantitative stability in our experimental iso- and xenograft mouse models for colorectal cancer progression. A complex preclinical experimental set-up was established to separately test the different steps of tumour progression and the role of tumour microenvironment, respectively, focusing on the role of ‘CD44’ in this process.ResultsWe managed to present a colorectal cancer-specific CD44 ASP, which remained unchanged from cell lines throughout primary tumour formation and metastatic progression. Furthermore, we report a unique roster of all expressed CD44 variant isoforms characteristic to colorectal cancer. Finally, on quantitative assessment of the variable exons v3 and v6, higher co-expression levels were found to be characteristic to metastatically potent tumour cells.ConclusionParticular CD44 variant isoforms seem to act as “metastasis genes” via tumour microenvironment-driven shifts in v3 and v6 expressions. However, this function may just affect a minority of tumour subclones. This fact and the huge potential number of different CD44 splice variants that can contain v3 and v6 domains can explain incoherence of clinical studies regarding functional asessment of CD44 variants, as well as diminish the chances of using CD44 variants for predictive purpose.

Highlights

CD44 is considered as ‘a’ metastasis associated gene, despite the fact that it is an umbrella term for a group of molecules produced from a single gene by alternative splicing
The complete CD44 isoform list was not achieved, we identified simplified colorectal adenocarcinoma specific CD44 alternative splice pattern (ASP) which was qualitatively stable across samples from different colorectal cancer cell lines in vitro, and subcutaneous, intrasplenic and orthotopic implanted primary colorectal tumours and their liver metastases/colonies
It is likely to assume that tumour microenvironment have a central role in metastatic phenotype presentation of primary colorectal cancer

Summary

Introduction

CD44 is considered as ‘a’ metastasis associated gene, despite the fact that it is an umbrella term for a group of molecules produced from a single gene by alternative splicing. Little consideration is given to the above in the literature of colorectal carcinomas as well as other tumour types, leading to confusion and contradictory results about its possible role in tumour progression. A variety of genes have been described and extensively investigated in the literature as key candidates in the tumorigenesis and progression of colorectal carcinoma, including APC, p53, K-ras, BRAF, DCC, MSH, EGFR, SFK, TGFR2, SMAD4, etc. One of the candidates of key importance has been CD44 It is one of the most investigated molecules in the metastatic process of several malignancies [7,8,9,10,11,12,13], among them that of colorectal cancer [14,15,16]

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