Cloning and Characterization of a Novel Isoform of Iodotyrosine Dehalogenase 1 (DEHAL1) DEHAL1C from Human Thyroid: Comparisons with DEHAL1 and DEHAL1B

The human iodotyrosine dehalogenase 1 (DEHAL1) gene is composed of six exons. Two isoforms (DEHAL1 and DEHAL1B) have been published in GenBank, both of which have a nitroreductase domain and arise from differential splicing in exon 5. We recently showed that the DEHAL1 isoform is a transmembrane protein that efficiently catalyzes the NADPH-dependent deiodination of mono (L-MIT) and diiodotyrosine (L-DIT) in human embryonic kidney-293 (HEK293) cells. In the present study, we establish the existence of a new transcript, DEHAL1C, in the human thyroid with a terminal exon that lacks in the DEHAL1 transcript. This exon is the complete exon 5, which is spliced in the DEHAL1B mRNA variant. These two variants encode proteins with differing C-terminal domains. Using quantitative reverse transcription polymerase chain reaction, we found that the expression of the mRNA of DEHAL1C and DEHAL1B was lower than that of DEHAL1 mRNA in the thyroid. We also observed that human DEHAL1B and DEHAL1C proteins are rapidly degrad...