title: Abnormal NF-kappaB signaling pathway with enhanced susceptibility to apoptosis in immortalized keratinocytes.
abstract: 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.
authors.affiliation: Department of Pathology, Loyola University Medical Center, Skin Cancer Research Laboratories, Cardinal Bernardin Center, Building #112, 2160 South First Avenue, 60153, Maywood, IL, USA.
authors.forename: V
authors.initials: V
authors.lastname: Chaturvedi
authors.forename: J Z
authors.initials: JZ
authors.lastname: Qin
authors.forename: M F
authors.initials: MF
authors.lastname: Denning
authors.forename: D
authors.initials: D
authors.lastname: Choubey
authors.forename: M O
authors.initials: MO
authors.lastname: Diaz
authors.forename: B J
authors.initials: BJ
authors.lastname: Nickoloff
mesh_terms: D017209:Apoptosis; D002461:Cell Line, Transformed; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism* / Q000473:pathology*; D016328:NF-kappa B / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D016328:NF-kappa B