Skip to main content
ARS Home » Northeast Area » Boston, Massachusetts » Jean Mayer Human Nutrition Research Center On Aging » Research » Publications at this Location » Publication #166335
Title: REGULATION OF THE UBIQUITIN PROTEASOME PATHWAY IN HUMAN LENS EPITHELIAL CELLS DURING THE CELL CYCLE

Author
item LU, QING - TUFTS-HNRCA
item SHANG, FU - TUFTS-HNRCA
item GUO, WEIMIN - TUFTS-HNRCA
item HOBBS, MARISA - TUFTS-HNRCA
item VALVERDE, PALOMA - TUFTS-HNRCA
item REDDY, VENKAT - KELLOG EYE CENTER
item TAYLOR, ALLEN - TUFTS-HNRCA

Submitted to: Experimental Eye Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2003
Publication Date: 2/1/2004
Citation: Lu, Q., Shang, F., Guo, W., Hobbs, M., Valverde, P., Reddy, V., Taylor, A. 2004. Regulation of the ubiquitin proteasome pathway in human lens epithelial cells during the cell cycle. Experimental Eye Research. 78(2):197-205.

Interpretive Summary: Most reproducing cells follow a series of orderly transitions from one phase to another. These shifts are usually controlled by the timed decomposition of cell cycle regulators by the ubiquitin-proteasome pathway. Objectives of this study were to characterize the timing of the phases of the human lens epithelial cell cycle and to explore potential functions of critical components of the ubiquitin-proteasome pathway in controlling lens cell cycle. Human lens epithelial cells were synchronized at G0/G1 phase by contact inhibition. FACS analysis monitored the cell cycle's progression. Proteasome inhibition experiments indicate that proteolysis is the predominant process that is responsible for the variations in regulators during the cell cycle. Levels of ubiquitin conjugating enzymes (E2s) Ubc7 and Ubc10 increased during the cell's growth period, Interphase and decreased upon completion of nuclear division, mitosis. In contrast, levels of ubiquitin activating enzymes E1, Ubc3 and Cul1 remained constant. The up regulation of Ubc7 and Ubc10 during the G2/M and S/G2/M phases suggests that these enzymes may be involved in controlling the cell cycle progression at this phase. Taken together, the data indicates that key components of the UPP in the human lens epithelial cells are regulated in a cell cycle-dependent manner.

Technical Abstract: Most proliferating cells follow a series of orderly transitions from one phase to another. These transitions are usually controlled by timed degradation of cell cycle regulators by the ubiquitin-proteasome pathway (UPP). There are no published reports regarding the timing of phases of the human lens cell cycle or regarding cell cycle-related changes in UPP components. Objectives of this study were to characterize the timing of the phases of the human lens epithelial cell cycle and to explore potential functions of critical components of the UPP in controlling lens cell cycle. Human lens epithelial cells were synchronized at G0/G1 phase by contact inhibition. Cell cycle progression upon subculturing was monitored by FACS analysis. It took ~40 h for HLEC to complete one cell cycle, ~20 hours for G1 phase, ~8-10 hours for S phase and ~10 hours for the combination of G2 and M phases. Proteasome-dependent degradation of p21**WAF and p27**Kip, the dominant Cdk inhibitors, was associated with the G1-S phase transition in these cells. Proteasome inhibition experiments indicate that proteolysis is the predominant process which is responsible for the variations in these regulators during the cell cycle. Levels of specific ubiquitin conjugating enzymes, Ubc7 and Ubc10, increased 6 and 2-fold at the G2/M phase and S/G2/M phases, respectively. Levels of these E2s decreased precipitously upon completion of the M phase. In contrast, levels of ubiquitin activating enzyme (E1) and Ubc3 remained constant during the cell cycle. Cul1, a component of the SCF (an E3), remained relatively constant during cell cycle. The up regulation of Ubc7 and Ubc10 during the G2/M and S/G2/M phases suggests that these enzymes may be involved in controlling the cell cycle progression at this phase. Taken together, the data indicate that expression of key components of the UPP in the human lens epithelial cells is regulated in a cell cycle-dependent manner. Some of the variations in levels of ubiquitin conjugating enzymes are suggestive of previously undescribed functions.