The ENTPD5/mt-PCPH oncoprotein is a catalytically inactive member of the ectonucleoside triphosphate diphosphohydrolase family.
Expression of the ENTPD5/mt-PCPH onco-protein and overexpression of the normal ENTPD5/PCPH protein contribute to the malignant transformation of diverse mammalian cell types, and PCPH is mutated and/or deregulated in various human tumor types. Expression of PCPH or mt-PCPH caused similar phenotypes, yet the effects promoted by mt-PCPH expression were consistently and substantially greater. ATP depletion and increased stress‑resistance are phenotypes commonly associated with PCPH and mt-PCPH expression. It was suggested that the intrinsic nucleoside triphosphate diphosphohydrolase (NTPDase) activity of PCPH and mt-PCPH may be responsible for these phenotypes, but direct supporting evidence remains to be established. Results from experiments designed to test such hypothesis demonstrate that, as expected, mt-PCPH expression in human colorectal carcinoma (CRC) cells decreased their ATP levels and conferred resistance to oxaliplatin, a colorectal cancer-relevant chemotherapeutic agent. Using a combination of site-directed mutagenesis, immunoprecipitation methods, in vitro enzyme activity assays and in situ enzyme activity determinations in live cells, this report also demonstrates that the mt-PCPH oncoprotein lacks detectable NTPDase activity, indicating that direct ATP cleavage by mt-PCPH did not cause the ATP depletion observed in mt-PCPH-expressing CRC cells. These results strongly suggest that the mt-PCPH oncoprotein may regulate the cellular energy levels and subsequent chemoresistance by an NTPDase-independent mechanism. Understanding possible alternative mechanisms will be essential to devise strategies for the successful treatment of predictably therapeutically resistant tumors expressing either increased PCPH levels or, particularly, the mt-PCPH oncoprotein.
Department of Radiation Medicine, Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, DC, USA.
Caitlin M
CM
MacCarthy
Vicente
V
Notario
D000255:Adenosine Triphosphate / Q000235:genetics / Q000378:metabolism; D000818:Animals; D015703:Antigens, CD / Q000235:genetics* / Q000378:metabolism; D001081:Apyrase / Q000235:genetics* / Q000378:metabolism; D063646:Carcinogenesis; D002384:Catalysis; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology; D006801:Humans; D016297:Mutagenesis, Site-Directed; D015513:Oncogene Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011755:Pyrophosphatases / Q000737:chemistry / Q000235:genetics*
D015703:Antigens, CD; D015513:Oncogene Proteins; D000255:Adenosine Triphosphate; C117634:ENTPD5 protein, human; D011755:Pyrophosphatases; D001081:Apyrase; C067869:CD39 antigen