PTPRK negatively regulates transcriptional activity of wild type and mutated oncogenic beta-catenin and affects membrane distribution of beta-catenin/E-cadherin complexes in cancer cells.
Previous reports showed that receptor-type protein-tyrosine phosphatase PTPRK co-localizes with beta-catenin at adherens junctions, and in vitro experiments suggested that beta-catenin could be substrate of PTPRK-mediated phosphatase activity. beta-catenin is a molecule endowed with a dual function being involved both in cell adhesion and in Wnt signaling pathway. Here we provide evidence for the role of PTPRK in negatively regulating the beta-catenin transcriptional activity by modulating its intracellular and membrane distribution. Expression of PTPRK protein in HEK293 cells and in PTPRK-null melanoma cell lines, one of which harbors a mutated oncogenic beta-catenin, impairs nuclear accumulation of wild type and oncogenic forms of beta-catenin, limits cytosolic levels of tyrosine-phosphorylated beta-catenin, and leads to re-localization of E-cadherin/beta-catenin complexes in ordered membrane phase along cell-cell contacts. This re-modulation of beta-catenin cellular distribution results in the inhibition of cyclin D1 and c-myc protein expression, whose genes are targets of beta-catenin. Tumor cells upon re-expression of PTPRK have a reduced proliferative and migration capacity. Moreover we show that PTPRK is also active in negatively regulating the transactivating function of beta-catenin in normal melanocytes as confirmed by experiments with silenced PTPRK by specific siRNA. Our data show that PTPRK influences transactivating activity of beta-catenin in non-tumoral and neoplastic cells by regulating the balance between signaling and adhesive beta-catenin, thus providing biochemical basis for the hypothesis of PTPRK as a tumor suppressor gene.
Novellino
Luisa
L
Unit of Immunotherapy of Human Tumors, Department of Experimental Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
De Filippo
Annamaria
A
Deho
Paola
P
Perrone
Federica
F
Pilotti
Silvana
S
Parmiani
Giorgio
G
Castelli
Chiara
C
D015820:Cadherins / Q000737:chemistry / Q000378:metabolism*; D045744:Cell Line, Tumor; D016147:Genes, Tumor Suppressor; D006801:Humans; D008545:Melanoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000556:secondary; D008954:Models, Biological; D046912:Multiprotein Complexes; D009154:Mutation; D034741:RNA, Small Interfering / Q000235:genetics; D054623:Receptor-Like Protein Tyrosine Phosphatases, Class 2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014158:Transcription, Genetic; D051176:beta Catenin / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
C495270:CTNNB1 protein, human; D015820:Cadherins; D046912:Multiprotein Complexes; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; D051176:beta Catenin; C489852:PTPRK protein, human; D054623:Receptor-Like Protein Tyrosine Phosphatases, Class 2