Transcriptome analysis reveals TMPRSS6 isoforms with distinct functionalities.

TMPRSS6 (matriptase-2) is a type II transmembrane serine protease involved in iron homoeostasis. At the cell surface of hepatocytes, TMPRSS6 cleaves haemojuvelin (HJV) and regulates the BMP/SMAD signalling pathway leading to production of hepcidin, a key regulator of iron absorption. Although four TMPRSS6 human isoforms and three mice Tmprss6 isoforms are annotated in databases (Ensembl and RefSeq), their relative expression or activity has not been studied. Analyses of RNA-seq data and RT-PCR from human tissues reveal that TMPRSS6 isoform 1 (TMPRSS6-1) and 3 are mostly expressed in human testis while TMPRSS6-2 and TMPRSS6-4 are the main transcripts expressed in human liver, testis and pituitary. Furthermore, we confirm the existence and analyse the relative expression of three annotated mice Tmprss6 isoforms. Using heterologous expression in HEK293 and Hep3B cells, we show that all human TMPRSS6 isoforms reach the cell surface but only TMPRSS6-1 undergoes internalization. Moreover, truncated TMPRSS6-3 or catalytically altered TMPRSS6-4 interact with HJV and prevent its cleavage by TMPRSS6-2, suggesting their potential role as dominant negative isoforms. Taken together, our results highlight the importance of understanding the precise function of each TMPRSS6 isoforms both in human and in mouse.