Abnormal NF-kappaB signaling pathway with enhanced susceptibility to apoptosis in immortalized keratinocytes.
The transcriptional activation and proper regulation of NF-kappaB is known to be important to the apoptotic resistant phenotype of epidermal-derived keratinocytes. By comparing and contrasting the responses of normal foreskin-derived keratinocytes versus an immortalized skin-derived keratinocyte cell line (i.e. HaCaT cells), several molecular defects involving NF-kappaB signaling pathway were delineated in the immortalized keratinocytes. While exposure to IFN-gamma plus TPA produces growth arrest in both normal and immortalized keratinocytes, with rapid phosphorylation of MEKKI and recruitment of distinctive protein kinase C isoforms into the signalosome complex, subsequent molecular events necessary for NF-kappaB activation were abnormal in HaCaT cells. This disrupted NF-kappaB activation in HaCaT cells was accompanied by enhanced susceptibility to UV-light induced apoptosis, which was associated with elevated levels of E2F-1 and decreased TRAF1/TRAF2 levels. Additional defects in HaCaT cells included markedly diminished levels of IKKbeta (and lack of induction of kinase activity) in response to inflammatory stimuli, a failure of p21(WAF1/CIP1) to associate with CDK2, and a decreased association between p65 and p300. These studies suggest caution in using HaCaT cells as a substitute for normal keratinocytes to study apoptosis in the skin. Thus, it appears that while the immortalized cells can escape cell cycle checkpoints by elevated levels of E2F-1, an adverse biological consequence of such dysregulated cell cycle control is the inability to activate the anti-apoptotic NF-kappaB signaling pathway. Therefore, exploiting this apoptosis vulnerability in pre-malignant, or immortalized cells, prior to acquiring a death-defying phenotype characteristic of more advanced malignant cell types, provides the basis for an early interventional therapeutic strategy for cutaneous oncologists.
Chaturvedi
V
V
Department of Pathology, Loyola University Medical Center, Skin Cancer Research Laboratories, Cardinal Bernardin Center, Building #112, 2160 South First Avenue, 60153, Maywood, IL, USA.
Qin
J Z
JZ
Denning
M F
MF
Choubey
D
D
Diaz
M O
MO
Nickoloff
B J
BJ
D017209:Apoptosis; D002461:Cell Line, Transformed; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism* / Q000473:pathology*; D016328:NF-kappa B / Q000378:metabolism*; D015398:Signal Transduction
D016328:NF-kappa B