Thyroid hormone receptor alpha1 follows a cooperative CRM1/calreticulin-mediated nuclear export pathway.
The thyroid hormone receptor alpha1 (TRalpha) exhibits a dual role as an activator or repressor of its target genes in response to thyroid hormone (T(3)). Previously, we have shown that TRalpha, formerly thought to reside solely in the nucleus bound to DNA, actually shuttles rapidly between the nucleus and cytoplasm. An important aspect of the shuttling activity of TRalpha is its ability to exit the nucleus through the nuclear pore complex. TRalpha export is not sensitive to treatment with the CRM1-specific inhibitor leptomycin B (LMB) in heterokaryon assays, suggesting a role for an export receptor other than CRM1. Here, we have used a combined approach of in vivo fluorescence recovery after photobleaching experiments, in vitro permeabilized cell nuclear export assays, and glutathione S-transferase pull-down assays to investigate the export pathway used by TRalpha. We show that, in addition to shuttling in heterokaryons, TRalpha shuttles rapidly in an unfused monokaryon system as well. Furthermore, our data show that TRalpha directly interacts with calreticulin, and point to the intriguing possibility that TRalpha follows a cooperative export pathway in which both calreticulin and CRM1 play a role in facilitating efficient translocation of TRalpha from the nucleus to cytoplasm.
Grespin
Matthew E
ME
Department of Biology, College of William and Mary, Williamsburg, Virginia 23187.
Bonamy
Ghislain M C
GMC
Department of Biology, College of William and Mary, Williamsburg, Virginia 23187.
Roggero
Vincent R
VR
Department of Biology, College of William and Mary, Williamsburg, Virginia 23187.
Cameron
Nicole G
NG
Department of Biology, College of William and Mary, Williamsburg, Virginia 23187.
Adam
Lindsay E
LE
Department of Biology, College of William and Mary, Williamsburg, Virginia 23187.
Atchison
Andrew P
AP
Department of Biology, College of William and Mary, Williamsburg, Virginia 23187.
Fratto
Victoria M
VM
Department of Biology, College of William and Mary, Williamsburg, Virginia 23187.
Allison
Lizabeth A
LA
Department of Biology, College of William and Mary, Williamsburg, Virginia 23187. Electronic address: laalli@wm.edu.
D021581:Active Transport, Cell Nucleus; D000818:Animals; D015153:Blotting, Western; D037282:Calreticulin / Q000378:metabolism*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D005982:Glutathione Transferase / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D028884:Karyopherins / Q000378:metabolism*; D051379:Mice; D008954:Models, Biological; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D037021:Thyroid Hormone Receptors alpha / Q000378:metabolism*; D000097606:Exportin 1 Protein
D037282:Calreticulin; D005231:Fatty Acids, Unsaturated; D005982:Glutathione Transferase; D028884:Karyopherins; D018160:Receptors, Cytoplasmic and Nuclear; D037021:Thyroid Hormone Receptors alpha; D000097606:Exportin 1 Protein; C038753:leptomycin B