title: pp32 (ANP32A) expression inhibits pancreatic cancer cell growth and induces gemcitabine resistance by disrupting HuR binding to mRNAs.
abstract: The expression of protein phosphatase 32 (PP32, ANP32A) is low in poorly differentiated pancreatic cancers and is linked to the levels of HuR (ELAV1), a predictive marker for gemcitabine response. In pancreatic cancer cells, exogenous overexpression of pp32 inhibited cell growth, supporting its long-recognized role as a tumor suppressor in pancreatic cancer. In chemotherapeutic sensitivity screening assays, cells overexpressing pp32 were selectively resistant to the nucleoside analogs gemcitabine and cytarabine (ARA-C), but were sensitized to 5-fluorouracil; conversely, silencing pp32 in pancreatic cancer cells enhanced gemcitabine sensitivity. The cytoplasmic levels of pp32 increased after cancer cells are treated with certain stressors, including gemcitabine. pp32 overexpression reduced the association of HuR with the mRNA encoding the gemcitabine-metabolizing enzyme deoxycytidine kinase (dCK), causing a significant reduction in dCK protein levels. Similarly, ectopic pp32 expression caused a reduction in HuR binding of mRNAs encoding tumor-promoting proteins (e.g., VEGF and HuR), while silencing pp32 dramatically enhanced the binding of these mRNA targets. Low pp32 nuclear expression correlated with high-grade tumors and the presence of lymph node metastasis, as compared to patients' tumors with high nuclear pp32 expression. Although pp32 expression levels did not enhance the predictive power of cytoplasmic HuR status, nuclear pp32 levels and cytoplasmic HuR levels associated significantly in patient samples. Thus, we provide novel evidence that the tumor suppressor function of pp32 can be attributed to its ability to disrupt HuR binding to target mRNAs encoding key proteins for cancer cell survival and drug efficacy.
authors.affiliation: Department of Surgery, Jefferson Pancreas, Biliary and Related Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania, United States of America.
authors.forename: Timothy K
authors.initials: TK
authors.lastname: Williams
authors.forename: Christina L
authors.initials: CL
authors.lastname: Costantino
authors.forename: Nikolai A
authors.initials: NA
authors.lastname: Bildzukewicz
authors.forename: Nathan G
authors.initials: NG
authors.lastname: Richards
authors.forename: David W
authors.initials: DW
authors.lastname: Rittenhouse
authors.forename: Lisa
authors.initials: L
authors.lastname: Einstein
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Cozzitorto
authors.forename: Judith C
authors.initials: JC
authors.lastname: Keen
authors.forename: Abhijit
authors.initials: A
authors.lastname: Dasgupta
authors.forename: Myriam
authors.initials: M
authors.lastname: Gorospe
authors.forename: Gregory E
authors.initials: GE
authors.lastname: Gonye
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Yeo
authors.forename: Agnieszka K
authors.initials: AK
authors.lastname: Witkiewicz
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Brody
mesh_terms: D000954:Antigens, Surface / Q000235:genetics / Q000378:metabolism*; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D015153:Blotting, Western; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D003842:Deoxycytidine Kinase / Q000235:genetics / Q000378:metabolism; D004351:Drug Resistance / Q000235:genetics; D051959:ELAV Proteins; D000067780:ELAV-Like Protein 1; D057809:HEK293 Cells; D006801:Humans; D010190:Pancreatic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D011485:Protein Binding; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000093542:Gemcitabine
chemical_list: D000954:Antigens, Surface; D000964:Antimetabolites, Antineoplastic; D051959:ELAV Proteins; D000067780:ELAV-Like Protein 1; C098770:ELAVL1 protein, human; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D003841:Deoxycytidine; D003842:Deoxycytidine Kinase; D000093542:Gemcitabine