Vitamin D3 and ceramide reduce the invasion of tumor cells through extracellular matrix components by elevating protein phosphatase-2A.
Increasing phosphorylation reactions by protein kinase A (PKA) or reducing dephosphorylation reactions of protein phosphatase-2A (PP-2A) increases the invasiveness of Lewis lung carcinoma (LLC) cells, as measured by their capacity to traverse extracellular matrix (ECM)-coated filters. Metastatic LLC-LN7 variants have reduced PP-2A activity when compared to nonmetastatic LLC-C8 variants. Immunoblotting showed that this reduced level of PP-2A activity was not due to reduced levels of the PP-2A catalytic (C) subunit. The cellular PP-2A activity could be stimulated by addition of C2-ceramide to LLC-LN7 lysates, or by incubating cells with either C2-ceramide or with a noncalcemic analog of vitamin D3, which has previously been shown to stimulate the release of ceramide. These treatments to elevate PP-2A activity in metastatic LLC-LN7 cells resulted in a decline in their capacity to invade through select (ECM) components, particularly through vitronectin and laminin. Underscoring the importance of PP-2A in limiting the invasiveness of tumor cells was the demonstration that LLC-LN7 cell transfectants overexpressing the PP-2A C alpha subunit were less invasive through ECM components than the wild-type cells. Invasion by these cells was further reduced by additionally increasing PP-2A activity by incubation with C2-ceramide or the vitamin D3 analog. These results suggest a role of a vitamin D3/ceramide/PP-2A pathway in limiting the invasiveness of tumor cells through select ECM components.
Metz
R J
RJ
Research Services, Hines VA Hospital, Hines, Ill., USA.
Vellody
K
K
Patel
S
S
Bergstrom
R
R
Meisinger
J
J
Jackson
J
J
Wright
M A
MA
Young
M R
MR
D000818:Animals; D015153:Blotting, Western; D002762:Cholecalciferol / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D005109:Extracellular Matrix / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D007797:Laminin / Q000378:metabolism; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000473:pathology*; D051379:Mice; D009361:Neoplasm Invasiveness; D009362:Neoplasm Metastasis; D019319:Okadaic Acid / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000096:biosynthesis / Q000187:drug effects / Q000378:metabolism*; D054648:Protein Phosphatase 2; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D014162:Transfection; D019096:Vitronectin / Q000378:metabolism
D007797:Laminin; C064769:N-acetylsphingosine; D019096:Vitronectin; D002762:Cholecalciferol; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D013110:Sphingosine