title: PKD2 and RSK1 Regulate Integrin β4 Phosphorylation at Threonine 1736.
abstract: The integrin α6β4, a major component of hemidesmosomes (HDs), stabilizes keratinocyte cell adhesion to the epidermal basement membrane through binding to the cytoskeletal linker protein plectin and association with keratin filaments. Disruption of the α6β4-plectin interaction through phosphorylation of the β4 subunit results in a reduction in adhesive strength of keratinocytes to laminin-332 and the dissolution of HDs. Previously, we have demonstrated that phosphorylation of T1736 in the C-terminal end of the β4 cytoplasmic domain disrupts the interaction of β4 with the plakin domain of plectin. Furthermore, we showed that β4-T1736 can be phosphorylated by PKD1 in vitro, and although both PMA and EGF induced T1736 phosphorylation, only PMA was able to activate PKD1. Here, we show that depletion of [Ca2+]i augments PMA- and EGF-induced phosphorylation of β4-T1736 and that this is caused by inhibition of the calcium-sensitive protein phosphatase calcineurin and augmentation of ERK1/2 activation. We also show that in keratinocytes the PMA-stimulated phosphorylation of β4-T1736 primarily is mediated by PKD2 activation downstream of PKCδ. On the other hand, both the EGF-stimulated phosphorylation of T1736 and the EGF-induced dissolution of HDs are dependent on a functional MAPK signaling pathway, and treatment with the RSK inhibitor BI-D1870 prevented EGF-stimulated phosphorylation of β4-T1736. Moreover, phosphorylation of β4-T1736 is enhanced by overexpression of wild-type RSK1, while it is reduced by the expression of kinase-inactive RSK1 or by siRNA-mediated depletion of RSK1. In summary, our data indicate that different stimuli can lead to the phosphorylation of β4-T1736 by either PKD2 or RSK1.
authors.affiliation: The Division of Cell Biology, The Netherlands Cancer Inst., Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
authors.forename: Lisa
authors.initials: L
authors.lastname: Te Molder
authors.affiliation: The Division of Cell Biology, The Netherlands Cancer Inst., Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
authors.forename: Arnoud
authors.initials: A
authors.lastname: Sonnenberg
mesh_terms: D019703:Calcineurin / Q000235:genetics / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000235:genetics / Q000378:metabolism; D002461:Cell Line, Transformed; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005786:Gene Expression Regulation; D022002:Hemidesmosomes / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D039161:Integrin alpha6beta4 / Q000235:genetics / Q000378:metabolism*; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051190:Plectin / Q000235:genetics / Q000378:metabolism; D051745:Protein Kinase C-delta / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011621:Pteridines / Q000494:pharmacology; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D050396:TRPP Cation Channels / Q000235:genetics / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013912:Threonine / Q000378:metabolism*; D000097794:Kalinin
chemical_list: D019703:Calcineurin; D002118:Calcium; D015815:Cell Adhesion Molecules; D004815:Epidermal Growth Factor; D039161:Integrin alpha6beta4; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D051190:Plectin; D051745:Protein Kinase C-delta; D011621:Pteridines; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D050396:TRPP Cation Channels; D013755:Tetradecanoylphorbol Acetate; D013912:Threonine; D000097794:Kalinin; C516541:BI D1870; C495332:PLEC protein, human; C069329:RPS6KA1 protein, human; C535150:MAPK1 protein, human