[Mechanism study on low dose tunicamycin inducing myeloma cells differentiation via unfolded protein response].

Objective: To explore the molecular mechanism of myeloma cell differentiation induced by low dose tunicamycin.

Method: U266 and RPMI8226 cells were incubated with low dose tunicamycin for 72h. Surface CD49e expression was assayed by flow cytometer (FCM), light chain protein in the cell culture supernatant by ELISA, the unfolded protein response (UPR) related gene GRP78 and GRP94 by real time PCR, and XBP1u and XBP1s transcription and translation changes by real time PCR and Western blot. After XBP1u gene was interfered with small RNA, and constructed plasmid was transfected into myeloma cells to up-regulated gene XBP-1u and XBP-1s reseparately, the differentiation of myeloma cells was observed again.

Results: Small dose tunicamycin could induce both U266 and RPMI8226 myeloma cells differentiation. Compared with the control group, cell morphology changed to mature feature, the nucleo- cytoplasm ratio decreased and nucleolus reduced or disappearance, CD49e expression increased the light chain protein concentration of cell culture supernatant was up-regulated and UPR related gene GRP78 and GRP94 were up-regulated during the differentiation. XBP-1u was up-regulated at both transcription and translation level, while XBP-1s down-regulated. After XBP1u gene expression interfered with small RNA, cell differentiation was disturbed. Cell differentiation was induced while XBP-1u gene was up-regulated by plasmid transfection.

Conclusion: Low dosage of tunicamycin could induce myeloma cell UPR and differentiation, while XBP-1u a key role during the process.