title: Cross-talk between epidermal growth factor receptor and protein kinase C during calcium-induced differentiation of keratinocytes.
abstract: The induction of epidermal differentiation by extracellular Ca2+ involves activation of both tyrosine kinase and protein kinase C (PKC) signaling cascades. To determine if the differentiation-dependent activation of tyrosine kinase signaling can influence the PKC pathway, we examined the tyrosine phosphorylation status of PKC isoforms in primary mouse keratinocytes stimulated to terminally differentiate with Ca2+. Elevation of extracellular Ca2+ induced tyrosine phosphorylation of PKC-delta, but not the other keratinocyte PKC isoforms (alpha, epsilon, eta, zeta). We have previously demonstrated that activation of the epidermal growth factor receptor (EGFR) pathway induces PKC-delta tyrosine phosphorylation in basal keratinocytes (Denning M F, Dlugosz A A, Threadgill D W, Magnuson T, Yuspa S H (1996) J Biol Chem 271: 5325-5331). When basal keratinocytes were stimulated to differentiate by Ca2+, the level of cell-associated transforming growth factor-alpha (TGF-alpha) increased 30-fold, while no increase in secreted TGF-alpha was detected. Furthermore, Ca2+-induced tyrosine phosphorylation of PKC-delta and phosphotyrosine-association of the receptor adapter protein Shc was diminished in EGFR -/- keratinocytes, suggesting that EGFR activation may occur during keratinocyte differentiation. Tyrosine phosphorylated PKC-delta was also detected in mouse epidermis, suggesting that this differentiation-associated signaling pathway is physiological. These results establish a requirement for the EGFR in Ca2+-induced tyrosine phosphorylation of PKC-delta, and document the production of cell-associated TGF-alpha in differentiated keratinocytes which may function independent of its usual mitogenic effects.
authors.affiliation: Laboratory of Cellular Carcinogenesis and Tumor Promotion, National Cancer Institute, Bethesda, MD, USA.
authors.forename: M F
authors.initials: MF
authors.lastname: Denning
authors.forename: A A
authors.initials: AA
authors.lastname: Dlugosz
authors.forename: C
authors.initials: C
authors.lastname: Cheng
authors.forename: P J
authors.initials: PJ
authors.lastname: Dempsey
authors.forename: R J
authors.initials: RJ
authors.lastname: Coffey
authors.forename: D W
authors.initials: DW
authors.lastname: Threadgill
authors.forename: T
authors.initials: T
authors.lastname: Magnuson
authors.forename: S H
authors.initials: SH
authors.lastname: Yuspa
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D000078404:Epidermal Cells; D004817:Epidermis / Q000378:metabolism; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism*; D015603:Keratinocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D051745:Protein Kinase C-delta; D020239:Receptor Cross-Talk; D016211:Transforming Growth Factor alpha / Q000096:biosynthesis; D014443:Tyrosine / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D016211:Transforming Growth Factor alpha; D014443:Tyrosine; C497259:Prkcd protein, mouse; D066246:ErbB Receptors; D011493:Protein Kinase C; D051745:Protein Kinase C-delta; D002118:Calcium