Regulation of Bcl-xL expression in human keratinocytes by cell-substratum adhesion and the epidermal growth factor receptor.
Cell-substratum adhesion is an essential requirement for survival of human neonatal keratinocytes in vitro. Similarly, activation of the epidermal growth factor receptor (EGF-R) has recently been implicated not only in cell cycle progression but also in survival of normal keratinocytes. The mechanisms by which either cell-substratum adhesion or EGF-R activation protect keratinocytes from programmed cell death are poorly understood. Here we describe that blockade of the EGF-R and inhibition of substratum adhesion share a common downstream event, the down-regulation of the cell death protector Bcl-xL. Expression of Bcl-xL protein was down-regulated during forced suspension culture of keratinocytes, concurrent with large-scale apoptosis. Similarly, EGF-R blockade was accompanied by down-regulation of Bcl-xL steady-state mRNA and protein levels to an extent comparable to that observed in forced suspension culture. However, down-regulation of Bcl-xL expression by EGF-R blockade was not accompanied by apoptosis; in this case, a second signal, generated by passaging, was required to induce rapid and large-scale apoptosis. These findings are consistent with the conclusions that (i) Bcl-xL represents a shared molecular target for signaling through cell-substrate adhesion receptors and the EGF-R, and (ii) reduced levels of Bcl-xL expression through EGF-R blockade lower the tolerance of keratinocytes for cell death signals generated by cellular stress.
Rodeck
U
U
The Wistar Institute, 3601 Spruce Street, Philadelphia, PA 19104, USA. RODECK@wista.wistar.upenn.edu
Jost
M
M
DuHadaway
J
J
Kari
C
C
Jensen
P J
PJ
Risse
B
B
Ewert
D L
DL
D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D017209:Apoptosis; D002448:Cell Adhesion; D002470:Cell Survival; D002478:Cells, Cultured; D002645:Chickens; D046508:Culture Techniques / Q000379:methods; D066246:ErbB Receptors / Q000502:physiology*; D006801:Humans; D007231:Infant, Newborn; D015603:Keratinocytes / Q000166:cytology / Q000502:physiology*; D007700:Kinetics; D008214:Lymphocytes / Q000502:physiology; D008297:Male; D016133:Polymerase Chain Reaction; D014176:Protein Biosynthesis; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis*; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger / Q000096:biosynthesis; D015398:Signal Transduction; D012867:Skin / Q000166:cytology*; D013997:Time Factors; D014158:Transcription, Genetic; D051020:bcl-X Protein
D000911:Antibodies, Monoclonal; C494811:BCL2L1 protein, human; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D051020:bcl-X Protein; D066246:ErbB Receptors