title: Cell-density-regulated chemotactic responsiveness of keratinocytes in vitro.
abstract: Keratinocytes represent the main constituents of the epidermis and have been found to play a regulatory role in a variety of inflammatory skin diseases. The functional activity of keratinocytes is highly heterogeneous, and depends on the cell localization in the epidermal architecture, and the maturation or differentiation state of the cells. Spontaneously proliferating HaCaT cells, showing several similarities to basal epidermal keratinocytes, were found to respond to external chemoattractants, including the chemokines RANTES (regulated on activation normal T cell expressed and secreted) and interleukin-8 and the mu-opioid agonist DAMGO ([d-ala2, N-Me-Phe4, Gly-ol5]enkephalin) in migration assays. The chemotactic responsiveness was highly dependent on the cell density of the monolayer, with greatest chemotactic activity at the highest cell density. Whereas RANTES was found to be the most potent chemoattractant, constitutive RANTES production was also detected in the HaCaT cultures. We found an inverse correlation between constitutive RANTES production and chemotactic responsiveness toward external RANTES, suggesting a possible functional down-modulation of the RANTES receptors, CC chemokine receptor 1 and CC chemokine receptor 5, during culture. Results from confocal laser scanning microscopy showed reduced CC chemokine receptor 1, but not CC chemokine receptor 5, expression by HaCaT cells at low cell densities, which was abolished in the presence of neutralizing antibodies against RANTES. The total CC chemokine receptor 1 pool (surface and intracellular receptors), however, showed no significant change during in vitro culture. Chemotactic responsiveness toward RANTES was directly correlated with the level of CC chemokine receptor 1 surface expression. Taken together these results show that with keratinocyte proliferation and the progressive increase in cell density there are dramatic alterations in keratinocyte function.
authors.affiliation: Department of Immunology and Microbiology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
authors.forename: I
authors.initials: I
authors.lastname: Szabo
authors.forename: M A
authors.initials: MA
authors.lastname: Wetzel
authors.forename: T J
authors.initials: TJ
authors.lastname: Rogers
mesh_terms: D002452:Cell Count; D002453:Cell Cycle; D002455:Cell Division / Q000502:physiology; D002461:Cell Line, Transformed; D002462:Cell Membrane / Q000378:metabolism; D002465:Cell Movement / Q000502:physiology; D018946:Chemokine CCL5 / Q000096:biosynthesis; D002633:Chemotaxis / Q000502:physiology*; D006801:Humans; D015603:Keratinocytes / Q000166:cytology* / Q000502:physiology*; D054389:Receptors, CCR1; D019713:Receptors, CCR5 / Q000378:metabolism; D019707:Receptors, Chemokine / Q000378:metabolism
chemical_list: C515300:CCR1 protein, human; D018946:Chemokine CCL5; D054389:Receptors, CCR1; D019713:Receptors, CCR5; D019707:Receptors, Chemokine