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Phosphorylation of the tumor suppressor p33^ING1b at Ser-126 influences its protein stability and proliferation of melanoma cells

Marco Garate^*, Eric I. Campos^*, Jason A. Bush, Hao Xiao and Gang Li^*,1

^* Department of Dermatology and Skin Science, Vancouver Coastal Health Research Institute, Jack Bell Research Centre, University of British Columbia, Vancouver, British Columbia, Canada;

Department of Biology, California State University–Fresno, Fresno, California, USA; and

ImmuneChem Pharmaceuticals Inc., Burnaby, British Columbia, Canada

¹Correspondence: Jack Bell Research Centre, 2660 Oak St., Vancouver, BC, Canada V6H 3Z6. E-mail: gangli{at}interchange.ubc.ca

ING (inhibitor of growth) tumor suppressors regulate cell-cycle checkpoints, apoptosis, and ultimately tumor suppression. Among the ING family members, p33^ING1b is the most intensively studied and plays an important role in the cellular stress response to DNA damage. Here we demonstrate that there is basal phosphorylation of p33^ING1b at Ser-126 in normal physiological conditions and that this phosphorylation is increased on DNA damage. The mutation of Ser-126 to alanine dramatically shortened the half-life of p33^ING1b. Furthermore, we found that both Chk1 and Cdk1 can phosphorylate this residue. Interestingly, while Cdk1 can phosphorylate p33^ING1b at Ser-126 in nonstress conditions, Chk1 predominantly phosphorylates this residue on DNA damage, which suggests that p33^ING1b is a downstream target of the ATM/ATR response cascade to genotoxic stress. More importantly, our data indicate that the Ser-126 residue plays a key role in regulating the expression of cyclin B1 and proliferation of melanoma cells.—Garate, M., Campos, E. I., Bush, J. A., Xiao, H., Li, G. Phosphorylation of the tumor suppressor p33^ING1b at Ser-126 influences its protein stability and proliferation of melanoma cells.

Key Words: protein half-life • cell proliferation