@article{shim_powers_ewing_zhu_smart_2005, title={Diminished expression of C/EBP alpha in skin carcinomas is linked to oncogenic Ras and reexpression of C/EBP alpha in carcinoma cells inhibits proliferation}, volume={65}, number={3}, journal={Cancer Research}, author={Shim, M. and Powers, K. L. and Ewing, S. J. and Zhu, S. and Smart, R. C.}, year={2005}, pages={861–867} }
 @article{shim_smart_2003, title={Lithium stabilizes the CCAAT/enhancer-binding protein alpha (C/EBP alpha) through a glycogen synthase kinase 3 (GSK3)-independent pathway involving direct inhibition of proteasomal activity}, volume={278}, ISSN={["0021-9258"]}, DOI={10.1074/jbc.M301356200}, abstractNote={CCAAT/enhancer-binding protein α (C/EBPα), a basic leucine zipper transcription factor, is involved in mitotic growth arrest and differentiation. Given that numerous proteins involved in cell cycle regulation are degraded via the ubiquitin-proteasome system, we examined whether the C/EBPα protein is degraded via a proteasomal mechanism. In cycloheximide-treated BALB/MK2 keratinocytes we found that C/EBPα is a short-lived protein with a half-life of ∼1 h. Treatment with proteasome inhibitors, MG-132 or lactacystin, blocked the degradation of the C/EBPα protein. Higher molecular weight species of ubiquitinated C/EBPα were detected in BALB/MK2, and in vitro studies confirmed that C/EBPα is degraded by the proteasome in an ATP- and ubiquitin-dependent manner. GSK3 is a known C/EBPα kinase and treatment of keratinocytes with LiCl, an inhibitor of GSK3 resulted in: (i) a 5-fold increase in C/EBPα protein levels, (ii) increased electrophoretic mobility of C/EBPα, and (iii) no increase in C/EBPα mRNA levels suggesting that GSK3-mediated phosphorylation of C/EBPα may target it for proteasomal degradation. However, a mutant C/EBPα containing T to A mutations in the GSK3 phosphorylation sites (T222A and T226A) retained its response to LiCl, and additional pharmacological inhibitors of GSK3 did not alter C/EBPα levels indicating the effects of LiCl on C/EBPα are GSK3-independent. LiCl treatment of BALB/MK2 cells inhibited C/EBPα degradation and produced a 6-fold increase in the half-life of C/EBPα protein. In vitro studies revealed that LiCl inhibited proteasome activity and the ensuing degradation of C/EBPα. These results demonstrate C/EBPα is degraded via a ubiquitin-dependent proteasomal pathway, and LiCl stabilizes C/EBPα through a GSK3-independent pathway involving direct inhibition of proteasome activity.}, number={22}, journal={JOURNAL OF BIOLOGICAL CHEMISTRY}, author={Shim, M and Smart, RC}, year={2003}, month={May}, pages={19674–19681} }