Na,K-ATPase β1-subunit is a target of sonic hedgehog signaling and enhances medulloblastoma tumorigenicity.
BACKGROUND
The Sonic hedgehog (Shh) signaling pathway plays an important role in cerebellar development, and mutations leading to hyperactive Shh signaling have been associated with certain forms of medulloblastoma, a common form of pediatric brain cancer. While the fundamentals of this pathway are known, the molecular targets contributing to Shh-mediated proliferation and transformation are still poorly understood. Na,K-ATPase is a ubiquitous enzyme that maintains intracellular ion homeostasis and functions as a signaling scaffold and a cell adhesion molecule. Changes in Na,K-ATPase function and subunit expression have been reported in several cancers and loss of the β1-subunit has been associated with a poorly differentiated phenotype in carcinoma but its role in medulloblastoma progression is not known.


METHODS
Human medulloblastoma cell lines and primary cultures of cerebellar granule cell precursors (CGP) were used to determine whether Shh regulates Na,K-ATPase expression. Smo/Smo medulloblastoma were used to assess the Na,K-ATPase levels in vivo. Na,K-ATPase β1-subunit was knocked down in DAOY cells to test its role in medulloblastoma cell proliferation and tumorigenicity.


RESULTS
Na,K-ATPase β1-subunit levels increased with differentiation in normal CGP cells. Activation of Shh signaling resulted in reduced β1-subunit mRNA and protein levels and was mimicked by overexpression of Gli1and Bmi1, both members of the Shh signaling cascade; overexpression of Bmi1 reduced β1-subunit promoter activity. In human medulloblastoma cells, low β1-subunit levels were associated with increased cell proliferation and in vivo tumorigenesis.


CONCLUSIONS
Na,K-ATPase β1-subunit is a target of the Shh signaling pathway and loss of β1-subunit expression may contribute to tumor development and progression not only in carcinoma but also in medulloblastoma, a tumor of neuronal origin.
Nemours/Alfred I. duPont Hospital for Children, Rockland Center I, 1701 Rockland Road, Wilmington, DE, 19803, USA.
Seung Joon
SJ
Lee
Nemours/Alfred I. duPont Hospital for Children, Rockland Center I, 1701 Rockland Road, Wilmington, DE, 19803, USA.
Alisa
A
Litan
Nemours/Alfred I. duPont Hospital for Children, Rockland Center I, 1701 Rockland Road, Wilmington, DE, 19803, USA.
Zhiqin
Z
Li
Nemours/Alfred I. duPont Hospital for Children, Rockland Center I, 1701 Rockland Road, Wilmington, DE, 19803, USA.
Bruce
B
Graves
Nemours/Alfred I. duPont Hospital for Children, Rockland Center I, 1701 Rockland Road, Wilmington, DE, 19803, USA.
Stephan
S
Lindsey
Nemours/Alfred I. duPont Hospital for Children, Rockland Center I, 1701 Rockland Road, Wilmington, DE, 19803, USA.
Sonali P
SP
Barwe
Nemours/Alfred I. duPont Hospital for Children, Rockland Center I, 1701 Rockland Road, Wilmington, DE, 19803, USA. langhans@nemoursresearch.org.
Sigrid A
SA
Langhans
D063646:Carcinogenesis / Q000235:genetics*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic; D055786:Gene Knockout Techniques; D053823:Hedgehog Proteins / Q000037:antagonists & inhibitors / Q000235:genetics*; D006801:Humans; D008527:Medulloblastoma / Q000235:genetics* / Q000473:pathology; D048054:Mitogen-Activated Protein Kinase 7 / Q000096:biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis; D015398:Signal Transduction / Q000235:genetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis* / Q000235:genetics; D014157:Transcription Factors / Q000096:biosynthesis; D000071676:Zinc Finger Protein GLI1
C400551:GLI1 protein, human; D053823:Hedgehog Proteins; D012333:RNA, Messenger; C509239:SHH protein, human; D014157:Transcription Factors; D000071676:Zinc Finger Protein GLI1; C481581:MAPK7 protein, human; D048054:Mitogen-Activated Protein Kinase 7; D000254:Sodium-Potassium-Exchanging ATPase