title: DARPP-32 increases interactions between epidermal growth factor receptor and ERBB3 to promote tumor resistance to gefitinib.
abstract: OBJECTIVE
  Dopamine and adenosine 3',5'-cyclic monophosphate-regulated phosphoprotein, Mr 32000 (DARPP-32), is overexpressed during gastric carcinogenesis. Gastric tumors can become resistant to gefitinib, an inhibitor of the epidermal growth factor receptor (EGFR). We investigated the role of DARPP-32 in gastric tumor resistance to gefitinib.
  
  
  METHODS
  Cell survival was determined by clonogenic survival and ATP-Glo Viability Assays. Apoptosis was assessed by Annexin-V and immunoblot analyses. The association between DARPP-32 and EGFR was evaluated by immunofluorescence and co-immunoprecipitation assays. Findings were validated in mice with gastric xenograft tumors. DARPP-32 expression was reduced using small hairpin RNAs in the human gastric cancer cell lines SNU-16 and MKN-45 cells.
  
  
  RESULTS
  Overexpression of DARPP-32 in MKN-28 cells, which do not normally express DARPP-32, blocked gefitinib-induced apoptosis and increased the drug's IC(50) 10-fold, compared to that of control cells (P < .01). Reduced expression of DARPP-32 in SNU-16 cells increased the sensitivity to gefitinib (P < .01). DARPP-32 activated phosphatidylinositol-3-kinase-AKT signaling, increased stability of the EGFR, and suppressed EGF- or gefitinib-induced degradation of the EGFR. DARPP-32 colocalized with EGFR on the cell membrane in a complex with EGFR and the EGF receptor ERBB3. DARPP-32-mediated resistance to gefitinib resulted from increased phosphorylation of and interaction between EGFR and ERBB3, which led to phosphorylation of AKT (at serine 473). Knockdown of DARPP-32 in gastric cancer cells reduced the mean size of tumors in mice and increased their response to gefitinib.
  
  
  CONCLUSIONS
  DARPP-32 promotes resistance of gastric cancer cells to gefitinib by promoting interaction between EGFR and ERBB3 and activating phosphatidylinositol-3-kinase-AKT signaling.
authors: Department of Surgery, Cancer Biology, and Vanderbilt-Ingram Cancer Center, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA.
authors: Shoumin
authors: S
authors: Zhu
authors: Abbes
authors: A
authors: Belkhiri
authors: Wael
authors: W
authors: El-Rifai
mesh_terms: D000230:Adenocarcinoma / Q000188:drug therapy / Q000473:pathology; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D004195:Disease Models, Animal; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32 / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm; D066246:ErbB Receptors / Q000378:metabolism*; D005260:Female; D000077156:Gefitinib; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011799:Quinazolines / Q000494:pharmacology / Q000627:therapeutic use*; D020893:Receptor, ErbB-3 / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013274:Stomach Neoplasms / Q000188:drug therapy* / Q000473:pathology
chemical_list: D000970:Antineoplastic Agents; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32; C497928:PPP1R1B protein, human; C497929:Ppp1r1b protein, mouse; D011799:Quinazolines; D019869:Phosphatidylinositol 3-Kinases; D066246:ErbB Receptors; D020893:Receptor, ErbB-3; D051057:Proto-Oncogene Proteins c-akt; D000077156:Gefitinib