title: Directional sensing of a phorbol ester gradient requires CD44 and is regulated by CD44 phosphorylation.
abstract: Cancer progression is associated with enhanced directional cell migration, both of the tumour cells invading into the stroma and stromal cells infiltrating the tumour site. In cell-based assays to study directional cell migration, phorbol esters are frequently used as a chemotactic agent. However, the molecular mechanism by which these activators of protein kinase C (PKC) result in the establishment of a polarized migratory phenotype is not known. Here we show that CD44 expression is essential for chemotaxis towards a phorbol ester gradient. In an investigation of CD44 phosphorylation kinetics in resting and stimulated cells, Ser316 was identified as a novel site of phosphorylation following activation of PKC. PKC does not phosphorylate Ser316 directly, but rather mediates the activation of downstream Ser316 kinase(s). In transfection studies, a phosphorylation-deficient Ser316 mutant was shown to act in a dominant-negative fashion to impair chemotaxis mediated by endogenous CD44 in response to a phorbol ester gradient. Importantly, this mutation had no effect on random cell motility or the ability of cells to migrate directionally towards a cocktail of chemoattractants. These studies demonstrate that CD44 functions to provide directional cues to migrating cells without affecting the motility apparatus.
authors.affiliation: Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London, UK.
authors.forename: G
authors.initials: G
authors.lastname: Tzircotis
authors.forename: R F
authors.initials: RF
authors.lastname: Thorne
authors.forename: C M
authors.initials: CM
authors.lastname: Isacke
mesh_terms: D000595:Amino Acid Sequence; D045744:Cell Line, Tumor; D002633:Chemotaxis; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D006801:Humans; D018960:Hyaluronan Receptors / Q000737:chemistry / Q000378:metabolism*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D018960:Hyaluronan Receptors; D015240:Phorbol 12,13-Dibutyrate; D012694:Serine; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate