Variant forms of upstream stimulatory factors (USFs) control the promoter activity of hTERT, the human gene encoding the catalytic subunit of telomerase

It is known that Myc regulates the expression of TERT, the telomerase catalytic subunit gene, by binding to E box. Here we show that another E box-binding protein, upstream stimulatory factor (USF), also regulates TERT expression. Specifically, the N-terminally truncated form of USF2 is present in telomerase-negative/resting human lymphocytes, but not in telomerase-positive/phytohemagglutinin-activated lymphocytes. In electrophoretic mobility shift assay, both full-length and truncated USF2s bound to the TERT E box. In a transient expression assay, the truncated USF had a dominant-negative effect on both exogenous full-length USF and endogenous positive regulators for activating TERT expression. These results suggest that the differential abundance of truncated USF2 may regulate telomerase activity during lymphocyte activation. (C) 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.