Confirmation of the biological significance of transthyretin as a biomarker for cutaneous T-cell lymphoma by its protein interaction partners.

We previously identified transthyretin (TTR) and its posttranslational modifications as a down-regulated marker in mycosis fungoides (MF), a benign subtype of cutaneous T-cell lymphoma (CTCL). In order to more precisely understand the biological role of TTR in the etiology of MF, it is essential to clarify the pathways of progression by identifying further interacting proteins. This study is the first to combine blue native polyacrylamide gel electrophoresis (BN-PAGE) with surface enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS) to detect new TTR interaction partners and to determine whether these TTR interaction partners can themselves be used as biomarkers. By this procedure, apolipoprotein A1, which was additionally found to be down-regulated in the serum of MF patients, apolipoprotein A4, retinol binding protein 4 (RBP-4), and retinoid X receptor β (RXR-β) were identified as interaction partners of TTR. The RXR family plays a role in cell differentiation and proliferation and is known to be the target of bexarotene, which is used in the treatment of CTCL. In conclusion, the combination of BN-PAGE and SELDI-TOF-MS used in this study allowed for the detection of protein interaction partners, which, in the case of RBP-4 and RXR, indicated a connection between the common tumor marker TTR and tumor progression in CTCL.