Thymosin-alpha 1 regulates MHC class I expression in FRTL-5 cells at transcriptional level

In this study we examined the effect of the synthetic peptide thymosin-alph a 1 (T alpha 1) on MHC class I expression in FRTL-5 cells. Treatment with T alpha 1 increased expression of MHC class I surface molecules and mRNA, wh ich reached its peak (153 +/- 8% of the control value) after 12 h. Chloramp henicol acetyltransferase (CAT) analysis, following transfection with a pla smid containing the regulatory sequence of MHC class I (or its deletion der ivatives) with the CAT reporter gene, and electrophoretic mobility shift as say experiments demonstrated that the action of T alpha 1 was at the transc riptional level, and its mechanism of action is likely due to increased bin ding between the complex p50/fra-2 and the enhancer A sequence of the 5' fl anking region of a swine class 1 gene (PD1). An increase in the expression of MHC class 1 surface molecules was also observed by flow cytometry in mur ine and human tumor cell lines and in primary cultures of human macrophages , This study shows for the first time an effect of T alpha 1 on the regulat ion of gene expression at the molecular level, and may further contribute t o explaining the results obtained using T alpha 1 in the control of infecti ous diseases and tumor growth.