title: Prolactin-induced PAK1 tyrosyl phosphorylation promotes FAK dephosphorylation, breast cancer cell motility, invasion and metastasis.
abstract: The serine/threonine kinase PAK1 is an important regulator of cell motility. Both PAK1 and the hormone/cytokine prolactin (PRL) have been implicated in breast cancer cell motility, however, the exact mechanisms guiding PRL/PAK1 signaling in breast cancer cells have not been fully elucidated. Our lab has previously demonstrated that PRL-activated tyrosine kinase JAK2 phosphorylates PAK1 on tyrosines 153, 201, and 285, and that tyrosyl phosphorylated PAK1 (pTyr-PAK1) augments migration and invasion of breast cancer cells.
  
  
  
  Here we further investigate the mechanisms by which pTyr-PAK1 enhances breast cancer cell motility in response to PRL. We demonstrate a distinct reduction in PRL-induced FAK auto-phosphorylation in T47D and TMX2-28 breast cancer cells overexpressing wild-type PAK1 (PAK1 WT) when compared to cells overexpressing either GFP or phospho-tyrosine-deficient mutant PAK1 (PAK1 Y3F). Furthermore, pTyr-PAK1 phosphorylates MEK1 on Ser298 resulting in subsequent ERK1/2 activation. PRL-induced FAK auto-phosphorylation is rescued in PAK1 WT cells by inhibiting tyrosine phosphatases and tyrosine phosphatase inhibition abrogates cell motility and invasion in response to PRL. siRNA-mediated knockdown of the tyrosine phosphatase PTP-PEST rescues FAK auto-phosphorylation in PAK1 WT cells and reduces both cell motility and invasion. Finally, we provide evidence that PRL-induced pTyr-PAK1 stimulates tumor cell metastasis in vivo.
  
  
  
  These data provide insight into the mechanisms guiding PRL-mediated breast cancer cell motility and invasion and highlight a significant role for pTyr-PAK1 in breast cancer metastasis.
authors.affiliation: Department of Biological Sciences, University of Toledo, 2801 W. Bancroft Street, Toledo, 43606-3390, OH, USA.
authors.forename: Alan
authors.initials: A
authors.lastname: Hammer
authors.affiliation: Department of Biological Sciences, University of Toledo, 2801 W. Bancroft Street, Toledo, 43606-3390, OH, USA. mdiakon@utnet.utoledo.edu.
authors.forename: Maria
authors.identifier: 0000-0002-4554-2730
authors.initials: M
authors.lastname: Diakonova
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000201:enzymology* / Q000473:pathology*; D002465:Cell Movement / Q000187:drug effects*; D004789:Enzyme Activation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000378:metabolism*; D020868:Gene Silencing / Q000187:drug effects; D006801:Humans; D051379:Mice; D008954:Models, Biological; D009361:Neoplasm Invasiveness; D009362:Neoplasm Metastasis; D010766:Phosphorylation / Q000187:drug effects; D019000:Phosphotyrosine / Q000378:metabolism*; D011388:Prolactin / Q000494:pharmacology*; D054594:Protein Tyrosine Phosphatase, Non-Receptor Type 12 / Q000037:antagonists & inhibitors / Q000378:metabolism; D054462:p21-Activated Kinases / Q000378:metabolism*
chemical_list: D019000:Phosphotyrosine; D011388:Prolactin; D051416:Focal Adhesion Protein-Tyrosine Kinases; C515903:PAK1 protein, human; D054462:p21-Activated Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; C516738:PTPN12 protein, human; D054594:Protein Tyrosine Phosphatase, Non-Receptor Type 12
keywords: Breast cancer cells; FAK; PAK1; Prolactin; Tyrosyl phosphorylation