A plausible role for actin gamma smooth muscle 2 (ACTG2) in small intestinal neuroendocrine tumorigenesis.
BACKGROUND
Small intestinal neuroendocrine tumors (SI-NETs) originate from the enterochromaffin cells in the ileum and jejunum. The knowledge about genetic and epigenetic abnormalities is limited. Low mRNA expression levels of actin gamma smooth muscle 2 (ACTG2) have been demonstrated in metastases relative to primary SI-NETs. ACTG2 and microRNA-145 (miR-145) are aberrantly expressed in other cancers and ACTG2 can be induced by miR-145. The aim of this study was to investigate the role of ACTG2 in small intestinal neuroendocrine tumorigenesis.


METHODS
Protein expression was analyzed in SI-NETs (n = 24) and in enterochromaffin cells by immunohistochemistry. The cell line CNDT2.5 was treated with the histone methyltransferase inhibitor 3-deazaneplanocin A (DZNep), the selective EZH2 inhibitor EPZ-6438, or 5-aza-2'-deoxycytidine, a DNA hypomethylating agent. Cells were transfected with ACTG2 expression plasmid or miR-145. Western blotting analysis, quantitative RT-PCR, colony formation- and viability assays were performed. miR-145 expression levels were measured in tumors.


RESULTS
Eight primary tumors and two lymph node metastases displayed variable levels of positive staining. Fourteen SI-NETs and normal enterochromaffin cells stained negatively. Overexpression of ACTG2 significantly inhibited CNDT2.5 cell growth. Treatment with DZNep or transfection with miR-145 induced ACTG2 expression (>10-fold), but no effects were detected after treatment with EPZ-6438 or 5-aza-2'-deoxycytidine. DZNep also induced miR-145 expression. SI-NETs expressed relatively low levels of miR-145, with reduced expression in metastases compared to primary tumors.


CONCLUSIONS
ACTG2 is expressed in a fraction of SI-NETs, can inhibit cell growth in vitro, and is positively regulated by miR-145. Theoretical therapeutic strategies based on these results are discussed.
Department of Surgical Sciences, Uppsala University, Uppsala University Hospital, Entrance 70, 1 tr, SE-75185, Uppsala, Sweden. katarina.edfeldt@surgsci.uu.se.
Katarina
K
Edfeldt
Department of Surgical Sciences, Uppsala University, Uppsala University Hospital, Entrance 70, 1 tr, SE-75185, Uppsala, Sweden.
Per
P
Hellman
Department of Surgical Sciences, Uppsala University, Uppsala University Hospital, Entrance 70, 1 tr, SE-75185, Uppsala, Sweden.
Gunnar
G
Westin
Department of Surgical Sciences, Uppsala University, Uppsala University Hospital, Entrance 70, 1 tr, SE-75185, Uppsala, Sweden.
Peter
P
Stalberg
D000199:Actins / Q000235:genetics / Q000502:physiology*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D063646:Carcinogenesis / Q000235:genetics*; D045744:Cell Line, Tumor; D004759:Enterochromaffin Cells / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007414:Intestinal Neoplasms / Q000235:genetics* / Q000473:pathology; D007421:Intestine, Small / Q000473:pathology; D035683:MicroRNAs / Q000502:physiology; D008875:Middle Aged; D018358:Neuroendocrine Tumors / Q000235:genetics* / Q000473:pathology; D055815:Young Adult
C579475:ACTG2 protein, human; D000199:Actins; C541010:MIRN145 microRNA, human; D035683:MicroRNAs
ACTG2; Epigenetic regulation; SI-NET; miR-145