Summary
Gαq plays a major role in platelet signal transduction, but little is known regarding
its transcriptional regulation. We have reported that Gαq is upregulated during phorbol
12-myristate 13-acetate (PMA)-induced megakaryocytic transformation of human erythroleukemia
(HEL) cells and regulated by EGR-1, an early growth transcription factor. These studies
focused on the initial 238 bp of the 5’ upstream region of the Gαq gene. In the present
studies we characterize a minimal region -1042/-1037 bp from ATG in the 5’ upstream
of the Gαq promoter that is associated with PMA responsiveness. In luciferase reporter
gene studies in HEL cells, Gαq 5’ upstream promoter sequence -1042/-1 showed an about
four-fold increased activity in PMA-treated compared to untreated cells. Deletion
of 6-nt-1042/-1037 eliminated the difference. Gel-shift studies on Gαq probe (-1042/-1012
bp) revealed binding of EGR-1 with PMA-treated but not untreated nuclear extracts,
and this was dependent on the sequence –1042/-1037.Silencing of endogenous EGR-1 inhibited
Gαq induction by PMA. MEK/ERK inhibitor U0126 blocked PMA effect on promoter activity
of the -1042/-1 construct. In conclusion, EGR-1 binding to sequence –1042/-1037 bp
in Gαq promoter mediates the induction of Gαq gene by PMA via the MEK/ERK signaling
pathway. These studies provide the first evidence of a PMA-responsive element in Gαq
promoter, and new insights into regulation of Gαq gene by EGR-1.
Keywords
EGR-1 - Gαq - MAP kinase - megakaryocytic differentiation - PMA responsive sequence