Homeodomain-interacting protein kinase-2 restrains cytosolic phospholipase A2-dependent prostaglandin E2 generation in human colorectal cancer cells.
OBJECTIVE
Homeodomain-interacting protein kinase-2 (HIPK2), a corepressor for homeodomain transcription factors, is a multifunctional kinase whose role in tumor cell survival is not completely clarified. We addressed whether HIPK2 restrains colon tumorigenesis by turning off cytosolic phospholipase A2 (cPLA2)-dependent prostaglandin E2 (PGE2) generation in the light of overwhelming evidence suggesting the contribution of this prostanoid in a variety of cancers.


METHODS
In the human colorectal cancer cell line, RKO, we studied the effect of RNA interference for HIPK2 (HIPK2i) on prostanoid biosynthesis, both in the absence and in the presence of the cPLA2 inhibitor arachidonyl trifluoromethyl ketone. We evaluated the role of HIPK2 in the cPLA2 gene regulation by reverse transcriptase-PCR, transcriptional activity, and chromatin immunoprecipitation analyses. The involvement of HIPK2 in tumorigenicity in vivo was studied by tumor growth of HIPK2i cells in nude mice. We compared the gene expression of HIPK2 and cPLA2 in human colorectal cancer specimens by reverse transcriptase-PCR.


RESULTS
HIPK2 silencing was associated with rousing PGE2 biosynthesis that was profoundly suppressed by the cPLA2 inhibitor. HIPK2 overexpression, along with histone deacetylase-1, inhibited the cPLA2-luc promoter that is strongly acetylated in HIPK2i cells. The tumors derived from HIPK2i cells injected in nude mice showed noticeably increased growth compared with parental cells. HIPK2 mRNA levels were significantly higher in colorectal cancers of patients with familial adenomatous polyposis, which showed undetectable cPLA2 levels compared with sporadic colorectal cancer expressing cPLA2.


CONCLUSIONS
Our findings reveal the novel mechanism of HIPK2 to restrain progression of human colon tumorigenesis, at least in part, by turning off cPLA2-dependent PGE2 generation.
D'Orazi
Gabriella
G
Department of Oncology and Neurosciences, Centre of Excellence on Aging, University G. d'Annunzio, Gabriele D'Annunzio University Foundation, Chieti, Italy. dorazi@ifo.it
Sciulli
Maria Gina
MG
Di Stefano
Valeria
V
Riccioni
Sabrina
S
Frattini
Milo
M
Falcioni
Rita
R
Bertario
Lucio
L
Sacchi
Ada
A
Patrignani
Paola
P
D000368:Aged; D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism*; D015232:Dinoprostone / Q000096:biosynthesis*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D020868:Gene Silencing; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D008875:Middle Aged; D010741:Phospholipases A / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D054467:Phospholipases A2; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction
D001095:Arachidonic Acids; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D012333:RNA, Messenger; C081565:arachidonyltrifluoromethane; C115114:HIPK2 protein, human; D017346:Protein Serine-Threonine Kinases; D010741:Phospholipases A; D054467:Phospholipases A2; D015232:Dinoprostone