title: Keratin 17 modulates hair follicle cycling in a TNFalpha-dependent fashion.
abstract: Mammalian hair follicles cycle between stages of rapid growth (anagen) and metabolic quiescence (telogen) throughout life. Transition from anagen to telogen involves an intermediate stage, catagen, consisting of a swift, apoptosis-driven involution of the lower half of the follicle. How catagen is coordinated, and spares the progenitor cells needed for anagen re-entry, is poorly understood. Keratin 17 (K17)-null mice develop alopecia in the first week post-birth, correlating with hair shaft fragility and untimely apoptosis in the hair bulb. Here we show that this abnormal apoptosis reflects premature entry into catagen. Of the proapoptotic challenges tested, K17-null skin keratinocytes in primary culture are selectively more sensitive to TNFalpha. K17 interacts with TNF receptor 1 (TNFR1)-associated death domain protein (TRADD), a death adaptor essential for TNFR1-dependent signal relay, suggesting a functional link between this keratin and TNFalpha signaling. The activity of NF-kappaB, a downstream target of TNFalpha, is increased in K17-null skin. We also find that TNFalpha is required for a timely anagen-catagen transition in mouse pelage follicles, and that its ablation partially rescues the hair cycling defect of K17-null mice. These findings identify K17 and TNFalpha as two novel and interdependent regulators of hair cycling.
authors.affiliation: Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
authors.forename: Xuemei
authors.initials: X
authors.lastname: Tong
authors.forename: Pierre A
authors.initials: PA
authors.lastname: Coulombe
mesh_terms: D000505:Alopecia / Q000235:genetics*; D000818:Animals; D017209:Apoptosis / Q000235:genetics; D002453:Cell Cycle / Q000235:genetics; D018859:Hair Follicle / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism; D007633:Keratins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008817:Mice, Mutant Strains; D016328:NF-kappa B / Q000378:metabolism; D015398:Signal Transduction; D053199:TNF Receptor-Associated Death Domain Protein; D047988:Tumor Necrosis Factor Receptor-Associated Peptides and Proteins / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism*
chemical_list: C118917:Krt17 protein, mouse; D016328:NF-kappa B; D053199:TNF Receptor-Associated Death Domain Protein; C481226:Tradd protein, mouse; D047988:Tumor Necrosis Factor Receptor-Associated Peptides and Proteins; D014409:Tumor Necrosis Factor-alpha; D007633:Keratins