AP-1/Egr1 puzzler

7 November 2000

Andrey Ryabinin

Here is a puzzle: in neural cells expression of Egr1 (aka Zif268, NGFI-A, krox-24, etc.) is often induced together with that of c-Fos. No surprise here, their promoters both have CRE and SRE sites. Sometimes Egr1 is induced, but c- Fos is not. This is also possible to explain: there are four SRE sites in egr1 and only one in c-fos promoter, plus these SRE's are not identical. Now we have found a treatment that strongly induces Fos, but not Egr. What could be involved in this?

We have tried to test for increased CREB phosphorylation (fos has more CRE sites than egr), and increased phosphorylation of Stat1, Stat3, Stat5, and Stat6 (fos has SIE elements, and egr not), and did not find any of them upregulated (well, we could have failed in our technique with some of them). What else could be involved in such differential regulation?