title: Proteasome-mediated degradation and functions of hematopoietic progenitor kinase 1 in pancreatic cancer.
abstract: Hematopoietic progenitor kinase 1 (HPK1) regulates stress responses, proliferation, and apoptosis in hematopoietic cells. In this study, we examined the expression, regulation, and functions of HPK1 in pancreatic ductal adenocarcinomas (PDA). We found that loss of HPK1 protein expression correlated significantly with the progression of pancreatic intraepithelial neoplasias (P = 0.001) and development of invasive PDA. Similarly, HPK1 protein was not expressed in any of eight PDA cell lines examined but was expressed in immortalized human pancreatic duct epithelial (HPDE) cells. There was no difference in HPK1 mRNA levels in PDA cell lines or primary PDA compared with those in HPDE cells or ductal epithelium in chronic pancreatitis and normal pancreas, respectively. Treatment of Panc-1 cells with a proteasome inhibitor, MG132, increased the HPK1 protein levels in a dose-dependent manner, suggesting that alteration in proteasome activity contributes to the loss of HPK1 protein expression in pancreatic cancer. Like the endogenous HPK1, both wild-type HPK1 and its kinase-dead mutant, HPK1-M46, overexpressed in Panc-1 cells, were also targeted by proteasome-mediated degradation. After MG132 withdrawal, wild-type HPK1 protein expression was markedly decreased within 24 hours, but kinase-dead HPK1 mutant protein expression was sustained for up to 96 hours. Therefore, HPK1 kinase activities were required for the loss of HPK1 protein in PDAs. Furthermore, restoring wild-type HPK1 protein in PDA cells led to the increase in p21 and p27 protein expression and cell cycle arrest. Thus, HPK1 may function as a novel tumor suppressor and its loss plays a critical role in pancreatic cancer.
authors.affiliation: Department of Gastrointestinal Medical Oncology, The University of Texas MD Anderson Cancer, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Hua
authors.initials: H
authors.lastname: Wang
authors.forename: Xianzhou
authors.initials: X
authors.lastname: Song
authors.forename: Craig
authors.initials: C
authors.lastname: Logsdon
authors.forename: Guisheng
authors.initials: G
authors.lastname: Zhou
authors.forename: Douglas B
authors.initials: DB
authors.lastname: Evans
authors.forename: James L
authors.initials: JL
authors.lastname: Abbruzzese
authors.forename: Stanley R
authors.initials: SR
authors.lastname: Hamilton
authors.forename: Tse-Hua
authors.initials: TH
authors.lastname: Tan
authors.forename: Huamin
authors.initials: H
authors.lastname: Wang
mesh_terms: D048708:Cell Growth Processes / Q000502:physiology; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000096:biosynthesis; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000096:biosynthesis; D018450:Disease Progression; D015536:Down-Regulation; D006801:Humans; D007150:Immunohistochemistry; D010190:Pancreatic Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D014162:Transfection
chemical_list: D050759:Cyclin-Dependent Kinase Inhibitor p21; D012333:RNA, Messenger; D050760:Cyclin-Dependent Kinase Inhibitor p27; C102102:hematopoietic progenitor kinase 1; D017346:Protein Serine-Threonine Kinases; D046988:Proteasome Endopeptidase Complex