Possible Involvement of YB-1 in Abnormal Nuclear Shape of Adult T-Cell　Leukemia/Lymphoma Cell

Background: Adult T-cell leukemia/lymphoma (ATL) cells contain extensive chromosomal abnormalities and some acute-type ATL patients show leukemic cells with highly lobulated nucleus, called "Flower cell". Thus, abnormality of nuclear shape seems to be associated with leukemogenesis of ATL. A previous report suggested that activation of PI3K is associated with the formation of the lobulated nucleus of ATL cells, but precise molecular mechanism underlying the flower-like nuclear shape remains unknown. Y-box-binding protein-1 (YB-1) functions in multiple layer of cellular processes, such as DNA replication and transcription, mRNA splicing and translation. Expression level of YB-1 is up-regulated in various types of cancers and related with chromosomal abnormality of breast cancer. We therefore hypothesized that YB-1 would be involved in the formation of the flower-like nuclear shape.

Methods: Expression of YB-1 was examined in HTLV-1 infected cell lines (ED, MT-1, and TBX-4B), non-infected cell lines (Jurkat and MOLT-4), and peripheral blood mononuclear cells (PBMCs) from healthy donors, HTLV-1 carriers, chronic-, and smoldering-type ATL patients by quantitative RT-PCR. The level of the protein expression was also analyzed by Western blotting. The subcellular localization of phosphorylated YB-1 (P-YB-1) was assessed by immunofluorescence staining.

Results: YB-1 was expressed abundantly in ED, MT-1 and Jurkat, in which lobulated nuclei were confirmed with Giemsa staining. The expression level of YB-1 in smoldering-type ATL tended to be higher than that in HTLV-1 carriers and healthy donors. YB-1 protein was detected in the all analyzed cell lines, but their expression level did not correlate with the quantitative RT-PCR results. Next, we analyzed the subcellular localization of YB-1 by immunofluorescence assay. We found that the phosphorylated YB-1 was accumulated in the lobulated nuclear region in an ATL cell line, ED cells. We also observed that Pericentrin, an integral component of the centrosome, was colocalized with the phosphorylated YB-1.

Conclusion: These data indicated that overexpression and phosphorylation of YB-1 might induce dysregulation of cell mitosis and contribute to formation of flower-cell formation in ATL cells.