Effect of Hypoxia-regulated Polo-like Kinase 3 (Plk3) on Human Limbal Stem Cell Differentiation.
Hypoxic conditions in the cornea affect epithelial function by activating Polo-like kinase 3 (Plk3) signaling and the c-Jun·AP-1 transcription complex, resulting in apoptosis of corneal epithelial cells. Hypoxic stress in the culture conditions also regulates limbal stem cell growth and fate. In this study, we demonstrate that there is a differential response of Plk3 in hypoxic stress-induced primary human limbal stem (HLS) and corneal epithelial (HCE) cells, resulting in different pathways of cell fate. We found that hypoxic stress induced HLS cell differentiation by down-regulating Plk3 activity at the transcription level, which was opposite to the effect of hypoxic stress on Plk3 activation to elicit HCE cell apoptosis, detected by DNA fragmentation and TUNEL assays. Hypoxic stress-induced increases in c-Jun phosphorylation/activation were not observed in HLS cells because Plk3 expression and activity were suppressed in hypoxia-induced HLS cells. Instead, hypoxic stress-induced HLS cell differentiation was monitored by cell cycle analysis and measured by the decrease and increase in p63 and keratin 12 expression, respectively. Hypoxic stress-induced Plk3 signaling to regulate c-Jun activity, resulting in limbal stem cell differentiation and center epithelial apoptosis, was also found in the corneas of wild-type and Plk3(-/-)-deficient mice. Our results, for the first time, reveal the differential effects of hypoxic stress on Plk3 activity in HLS and HCE cells. Instead of apoptosis, hypoxic stress suppresses Plk3 activity to protect limbal stem cells from death and to allow the process of HLS cell differentiation.
From the Department of Medicine, David Geffen School of Medicine, University of California Los Angeles, Torrance, California 90502.
Ling
L
Wang
the Department of Ophthalmology, Julie Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, California 91020, and.
Sheyla
S
González
the Department of Environmental Medicine, New York University School of Medicine, Tuxedo, New York 10987.
Wei
W
Dai
the Department of Ophthalmology, Julie Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, California 91020, and.
Sophie
S
Deng
From the Department of Medicine, David Geffen School of Medicine, University of California Los Angeles, Torrance, California 90502, lluou@ucla.edu.
Luo
L
Lu
D000328:Adult; D000368:Aged; D000818:Animals; D017209:Apoptosis; D002454:Cell Differentiation; D015687:Cell Hypoxia; D053938:DNA Fragmentation; D019573:Epithelium, Corneal / Q000166:cytology / Q000201:enzymology*; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008875:Middle Aged; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis* / Q000235:genetics; D013234:Stem Cells / Q000166:cytology / Q000201:enzymology*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism; D000097868:Polo-like Kinases
D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D015534:Trans-Activators; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; C115051:TP63 protein, human; C486419:Trp63 protein, mouse; C486256:PLK3 protein, human; D000097868:Polo-like Kinases; C093328:Plk3 protein, mouse
c-Jun transcription factor; cell death; cell differentiation; cornea; epithelial cell; protein kinase; signal transduction; stem cells; transcription regulation