Chk2 Activation and Phosphorylation-Dependent Oligomerization

Abstract

The tumor suppressor gene CHK2 encodes a versatile effector serine/threonine kinase involved in responses to DNA damage. Chk2 has an amino-terminal SQ/TQ cluster domain (SCD), followed by a forkhead-associated (FHA) domain and a carboxyl-terminal kinase catalytic domain. Mutations in the SCD or FHA domain impair Chk2 checkpoint function. We show here that autophosphorylation of Chk2 produced in a cell-free system requires trans phosphorylation by a wortmannin-sensitive kinase, probably ATM or ATR. Both SQ/TQ sites and non-SQ/TQ sites within the Chk2 SCD can be phosphorylated by active Chk2. Amino acid substitutions in the SCD and the FHA domain impair auto- and trans-kinase activities of Chk2. Chk2 forms oligomers that minimally require the FHA domain of one Chk2 molecule and the SCD within another Chk2 molecule. Chk2 oligomerization in vivo increases after DNA damage, and when damage is induced by gamma irradiation, this increase requires ATM. Chk2 oligomerization is phosphorylation dependent and can occur in the absence of other eukaryotic proteins. Chk2 can cross-phosphorylate another Chk2 molecule in an oligomeric complex. Induced oligomerization of a Chk2 chimera in vivo concomitant with limited DNA damage augments Chk2 kinase activity. These results suggest that Chk2 oligomerization regulates Chk2 activation, signal amplification, and transduction in DNA damage checkpoint pathways.

We thank Michael Kastan and Susan Lees-Miller for plasmids and JoAnn Falato for secretarial assistance. We thank other members of the Stern laboratory for helpful comments, particularly Soo-Jung Lee, Jonathan McMenamin-Balano, and Marc F. Schwartz.

This work was supported by USAMRMC DAMD 17-98-1-8272, USPHS R01CA82257, and USAMRMC DAMD 17-01-1-0465 (X.X.), a Leslie H. Warner fellowship from the Yale Cancer Center (X.X.), an Anna Fuller fellowship in molecular oncology (L.T.), Susan G. Komen Breast Cancer Foundation fellowship PDF2000 719 (L.T.), and USAMRMC DAMD 17-01-1-0464 (L.T.).