Table 1.
Cellular localization and function of mammalian TRα and TRβ isoforms
| Receptors | Cellular localization | Known or hypothetical function(s) |
|---|---|---|
| TRα (NR1A1) | ||
| TRα1 | ||
| p46 (full-length) | Nuclear | Transcriptional activation/repression |
| p43 | Mitochondrial matrix | Transcriptional activation/repression |
| p33 | Unknown | Unknown |
| p30 | Plasma membrane | Signaling cascade |
| p28 | Mitochondrial inner membrane | Signaling cascade |
| TRα2 | Nuclear | Possible antagonist of TR action |
| TRα3 | Nuclear | Possible antagonist of TR action |
| TRΔα1 | Unknown | Possible antagonist of TR action |
| TRΔα2 | Unknown | Possible antagonist of TR action |
| TRα-ΔE6 | Cytoplasm | Inhibitor of TR activity |
| TRβ (NR1A2) | ||
| TRβ1 | Predominantly nuclear | Transcriptional activation/repression |
| TRβ2 | Predominantly nuclear | Transcriptional activation/repression |
| TRβ2Δ | Predominantly nuclear | Possible transcriptional regulation |
| TRβ3 | Predominantly nuclear | Transcriptional activation/repression |
| TRΔβ3 | Predominantly nuclear | Dominant negative antagonist |
| TRβ4 | Predominantly nuclear | Weak antagonist of TR action |