| Research Abstract |
We established a sarcomatoid cholangiocarcinoma cell line, ETK-1, and reported that the cell line could transdifferentiate into a hepatocytic lineage after treatment with 5-azacytidine. The converted cell line, MEK, also was successfully established. It seems likely that the demethylation effect of 5-azacytidine induces the newly expression of some genes that play a significant role in the differentiation process. To identify the key factors involved in this hepatocytic differentiation, we examined the differential gene display method in ETK-1 and MEK cell lines, and also in ETK-1 cells at various days after the 5-azacytidine treatment.
As a result, expression of B56δ gene, calcineuin B gene, and an unknown gene was upregulated during and after differentiation. B56δ is a regulatory subunit of protein phosphatase 2a (PP2A), whose one of known functions is the regulation of cell growth, cell division, differentiation, and signal transduction. For instance, when some cell lines are induced to differentiate with retinoic acid, expression of the B56δ increases significantly, which differentially targets PP2A to the nucleus. B56 expression has been found to be low in several tissue-culture cell lines but high in terminally differentiated tissues, such as the skeletal muscle and brain. Our data also support this distribution: B56δ was not detected in immature, undifferentiated cells (ETK-1), but it began to be expressed after induction of differentiation and was stably expressed in differentiated cells (MEK).
A subunit of another kind of protein phosphatase (calcineurin B, type I) and an unknown gene also showed interesting expression patterns after the induction of differentiation. We are currently carrying out additional experiments to verify whether B56δ and these proteins, along with other factors, are involved in the differentiation of cells along a hepatocytic lineage.
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