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.

Dual role of hematopoietic progenitor kinase 1 (HPK1) as a positive regulator of 1α,25-dihydroxyvitamin D-induced differentiation and cell cycle arrest of AML cells and as a mediator of vitamin D resistance

“…38 Consistent with the increased differentiation, G 1 arrest (G 1 /S ratio) also increases when QVD is used to inhibit HPK1 cleavage in DCS-treated 40AF cells (data not shown). A comparison of the abundance of the C-terminal cleaved fragment of HPK1 is principally expressed in hematopoietic cells 32 and is known to regulate stress responses, apoptosis and cell proliferation in cancer cells, 40 though in contrast to the current report, most previous studies focused on lymphoid cells. 35,41 An activation of cell membrane receptors forms a membrane-proximal complex that includes several small adaptor proteins, such as Grb2 and SLP-76 families containing the SH2 domain, 42,43 and HPK1 is subject to phosphorylation by this complex.…”

“…The involvement of HPK1 in cell cycle regulation is also supported by the recent report that restoration of wild-type HPK1 in pancreatic ductal carcinoma cells increases p21 and p27 expression and leads to cell cycle arrest. 40 This finding adds to the known control by 1,25D of cell cycle regulators, which include MAPK influence on pRb, 52 the AKT pathway 15 and the regulation of p27/Kip1 by the Cot1/Tpl2 oncogene 53 and microRNA181. 54 The caspase-mediated cleavage of HPK1 in 1,25D-resistant cells demonstrated in Figures 5C and 6C has been observed in previous studies, but not as the basis for cell resistance to treatment.…”

Aurora Kinase A Promotes Ovarian Tumorigenesis through Dysregulation of the Cell Cycle and Suppression of BRCA2

“…For ovarian cancer, 223 high-grade serous carcinoma cases, including 167 cases before and 56 cases postchemotherapy, were analyzed. Pancreatic cancer arrays (124 cases) have been described previously (28). Breast (208 cases) and colon (210 cases) tissue arrays were obtained from a commercial resource (Pantomics) without identifiers.…”

Overexpression of Protein Phosphatase 4 Correlates with Poor Prognosis in Patients with Stage II Pancreatic Ductal Adenocarcinoma

“…Frozen OCT-embedded human samples of primary PDAC and benign pancreatic tissue were microdissected and total RNA isolation was performed as described previously (11). One microgram of total RNA was reverse transcribed using the avian myeloblastosis virus reverse transcriptase kit (Promega, Madison, WI) according to the manufacturer’s protocol.…”