Abstract
The human HMG-I/Y gene, encoding the non-histone "high mobility group" proteins HMG-I and HMG-Y, is transcriptionally activated in human K562 erythroleukemia cells by treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA). TPA treatment induces differentiation of K562 cells within 2-4 days after treatment. In this report, we show that transcriptional activation of the HMG-I/Y gene is dependent on protein synthesis and is an early event (2 h after induction) in the TPA-mediated differentiation process. Of the four functional transcription start sites present in the gene, only one (start site 2) is preferentially induced upon TPA treatment. This is the first report, to our knowledge, of the preferential utilization of a specific transcription start site in response to a particular stimulus in a gene that contains multiple promoters. This indicates that each start site in the gene has the potential to be independently regulated instead of being coordinately controlled as shown in a number of other genes. In addition, sequences upstream of the inducible start site, which contains a TPA-responsive element, mediates TPA inducibility through AP1 (or an AP1-like) transcription factor. The HMG-I/Y proteins function as key regulators of gene expression and play a significant role in chromatin structural changes as well. The cloning and sequence analyses previously reported indicated the structure of the HMG-I/Y gene to be highly complex and predicted its expression to be tightly regulated. The results presented here confirm and extend these earlier findings.
Highlights
From the Wepartment of Biochemistry / Biophysics and the §Department of Genetics and Cell Biology, Washington State University, Pullman, Washington 99164-4660
We show that transcriptional activation of the HMG-IIY gene is dependent on protein synthesis and is an early event (2 h after induction) in the TPA-mediated differentiation process
We have previously shown that HMG-I/Y gene expression is induced upon TPA treatment of HUT-78 cells, a human T cell line [11]
Summary
SELECTIVE 12-0-TETRADECANOYLPHORBOL-13-ACETATE INDUCTION OF A SINGLE TRANSCRIPTION START SITE IN THE HMG-I/Y GENE*. Since HMG-I/Y proteins have been suggested to play important roles in regulating chromatin structure and gene transcription, both of which are important in the cellular differentiation process, we were interested to determine whether TPA induces HMG-I /Y gene expression in K562 cells and, if so, to determine the molecular mechanism of such an induction. Evidence is presented that demonstrates that the API (or an API-like) transcription factor mediates TPA inducibility To our knowledge, this is the first report of the preferential utilization of a single specific transcription start site in a promoter that contains multiple transcription start sites in response to an inducer of cellular differentiation
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