Thyroid hormone receptor alpha sumoylation modulates white adipose tissue stores

Abstract

Thyroid hormone (TH) and thyroid hormone receptor (THR) regulate stem cell proliferation and differentiation during development, as well as during tissue renewal and repair in the adult. THR undergoes posttranslational modification by small ubiquitin-like modifier (SUMO). We generated the THRA (K283Q/K288R)−/− mouse model for in vivo studies and used human primary preadipocytes expressing the THRA sumoylation mutant (K283R/K288R) and isolated preadipocytes from mutant mice for in vitro studies. THRA mutant mice had reduced white adipose stores and reduced adipocyte cell diameter on a chow diet, compared to wild-type, and these differences were further enhanced after a high fat diet. Reduced preadipocyte proliferation in mutant mice, compared to wt, was shown after in vivo labeling of preadipocytes with EdU and in preadipocytes isolated from mice fat stores and studied in vitro. Mice with the desumoylated THRA had disruptions in cell cycle G1/S transition and this was associated with a reduction in the availability of cyclin D2 and cyclin-dependent kinase 2. The genes coding for cyclin D1, cyclin D2, cyclin-dependent kinase 2 and Culin3 are stimulated by cAMP Response Element Binding Protein (CREB) and contain CREB Response Elements (CREs) in their regulatory regions. We demonstrate, by Chromatin Immunoprecipitation (ChIP) assay, that in mice with the THRA K283Q/K288R mutant there was reduced CREB binding to the CRE. Mice with a THRA sumoylation mutant had reduced fat stores on chow and high fat diets and reduced adipocyte diameter.

RNA-sequencing reveals strong predominance ofTHRAsplicing isoform 2 in the developing and adult human brain

“…In particular, dephosphorylation of THRα2 has been shown to increase the DNA binding affinity and thus the inhibitory function of THRα2 23 and sumoylation has been shown to affect interaction with other TRs and thus gene expression. 24,25 Together, our findings with the detected difference in THRα1 versus THRα2 expression should be kept in mind when inferring biological mechanisms from molecular studies that do not distinguish between the two isoforms. Further expression studies should investigate the isoform expression pattern at later stages of fetal brain development and at postnatal life stages.…”

“…In particular, dephosphorylation of THR α 2 has been shown to increase the DNA binding affinity and thus the inhibitory function of THR α 2 23 and sumoylation has been shown to affect interaction with other TRs and thus gene expression. 24,25…”

TRα2—An Untuned Second Fiddle or Fine-Tuning Thyroid Hormone Action?

“…Moreover, sumoylation of TRs at lysine (K) residues affects the interaction of TRs with other transcription factors, as well as gene induction and repression [64]. TRα1 has two main sumoylation sites at K283 and K389 and an alternative sumoylation site at K288 that can compensate for K283 [65]. While K389 lies within the TRα1-specific region of the C-terminus, K283 and K288 are located within a region shared by both isoforms.…”