Short-chain fatty acids and thyroid hormone interact in regulating enterocyte gene transcription

Background. Enterocyte differentiation is known to be regulated by a variet y of extracellular compounds, among which are triiodothyronine (T-3) and th e short-chain fatty acids (SCFAs). Because several SCFAs are known to induc e histone hyperacetylation, and T-3 action has been recently linked to chro matin structure, we sought to investigate the interplay between SCFAs and T -3 in regard to the enterocyte differentiation marks intestinal alkaline ph osphatase (IAP). Methods. Caco-2 cells were transiently transfected with a reporter construc t containing 2.4 kb of the human IAP gene 5' flanking region (IAP(2.4)CAT). Cotransfections were carried out with and without thyroid hormone receptor -1 (TR beta-1) or histone deacetylase-1 (HDAC-1) expression plasmids. Cells were treated with 5 mmol/L SCFAs (propionic, butyric, valeric, or caproic acids as propionate, butyrate, valerate, or caproate, respectively), with a nd without 10 nmol/L T-3. Reporter gene activity was measured and the level of histone acetylation assessed by means of acid-urea-triton (AUT) gel ass ays. Results, TR beta-1 cotransfection caused a mal kpd decrease in IAP rep orter gene activity, which is consistent with the well-known phenomenon of ligand independent repression (LIR), whereas T-3 treatment reversed the LIR and caused further reporter gene activation. Treatment with SCFAs similarl y resulted in a complete blockage of LIR, and, in fact, turned the TRP-I in to a transcriptional activator even in the absence of T-3. Concomitant trea tment with T-3 and butyric acid produced an additive effect on IAP transact ivation. In contrast, cotransfection with HDAC-1 attenuated the effects of SCFAs on IAP gene activation. AUT gel studios demonstrated histone hyperace tylation in response to SCFA treatment. Conclusion. One or more DNA cis-ele ments in the human IAP gene mediate ligand independent repression the TR be ta-1, an effect that can be entirely reversed by those SCFAs that induce hi stone hyperacetylation. In addition T-3 and SCFAs can act in concert to ind uce IAP gene transcription, demonstrating an important link between triiodo thyronine and histone hyperacetylation in regard to enterocyte-specific gen e expression.