Nuclear actin has been implicated in different nuclear functions. In this work, its localization in nuclear membrane, chromatin
and nuclear lipid microdomains was investigated. The implication of sphingomyelin metabolism was studied.
Nuclear membrane, chromatin and nuclear lipid microdomains were purified from hepatocyte nuclei and H35 human hepatoma
cell nuclei. The presence of β-actin was analyzed with immunoblotting by using specific antibodies. Sphingomyelinase,
sphingomyelin-synthase, and phosphatidylcholine-specific phospholipase C activities were assayed by using radioactivity
sphingomyelin and phosphatidylcholine as substrate.
The results showed that β-actin is localized in nuclear lipid microdomains and it increases in cancer cells. Evidence is provided
to the difference of phosphatidylcholine and sphingomyelin metabolism in various subnuclear fractions of cancer cell
nuclei compared with normal cells. Our findings show increase of sphingomyelin-synthase and inhibition of sphingomyelinase
activity only in nuclear lipid microdomains.
Nuclear lipid microdomains, constituted by phosphatidylcholine, sphingomyelin and cholesterol, play a role as platform for
β-actin anchoring. Possible role of sphingomyelin metabolism in cancer cells is discussed.
