Phosphorylation of HMG-I by protein kinase C attenuates its binding affinity to the promoter regions of protein kinase C gamma and neurogranin/RC3 genes
Dm. Xiao et al., Phosphorylation of HMG-I by protein kinase C attenuates its binding affinity to the promoter regions of protein kinase C gamma and neurogranin/RC3 genes, J NEUROCHEM, 74(1), 2000, pp. 392-399
A 20-kDa DNA-binding protein that binds the AT-rich sequences within the pr
omoters of the brain-specific protein kinase C (PKC) gamma and neurogranin/
RC3 genes has been characterized as chromosomal nonhistone high-mobility-gr
oup protein (HMG)-I, This protein is a substrate of PKC alpha, beta, gamma,
and delta but is poorly phosphorylated by PKC epsilon and zeta. Two major
(Ser(44) and Ser(64)) and four minor phosphorylation sites have been identi
fied. The extents of phosphorylation of Ser(44) and Ser(64) were 1:1, where
as those of the four minor sites all together were <30% of the major one. T
hese PKC phosphorylation sites are distinct from those phosphorylated by cd
c2 kinase, which phosphorylates Thr(53) and Thr(78). Phosphorylation of HMG
-I by PKC resulted in a reduction of DNA-binding affinity by 28-fold as com
pared with 12-fold caused by the phosphorylation with cdc2 kinase, HMG-I co
uld be additively phosphorylated by cdc2 kinase and PKC, and the resulting
doubly phosphorylated protein exhibited a >100-fold reduction in binding af
finity. The two cdc2 kinase phosphorylation sites of HMG-I are adjacent to
the N terminus of two of the three predicted DNA-binding domains. In compar
ison, one of the major PKC phosphorylation sites, Ser(64), is adjacent to t
he C terminus of the second DNA-binding domain, whereas Ser(44) is located
within the spanning region between the first and second DNA-binding domains
. The current results suggest that phosphorylation of the mammalian HMG-I b
y PKC alone or in combination with cdc2 kinase provides an effective mechan
ism for the regulation of HMG-I function.