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. 2010 Jun 21;30(17):4149–4158. doi: 10.1128/MCB.00224-10

FIG. 6.

FIG. 6.

Downregulation of c-Myc by Aiolos and Ikaros is necessary for p27 induction and cyclin D3 downregulation. (A) The induction of p27 and downregulation of cyclin D3 by Aiolos and Ikaros are dependent on c-Myc downregulation in pre-B cells. The expression of p27 and cyclin D3 was examined in mRNA isolated from Aiolos- and Ikaros-infected Eμ-Myc pre-B cells (described in Fig. 3C). (B) Forced expression of p27 is sufficient to inhibit the proliferation of Eμ-Myc pre-B cells. Eμ-Myc pre-B cells were infected with virus expressing p27, and the effect of p27 on cell cycle progression was examined after 48 h. Infected cells expressing a high level of GFP-positive (p27) and GFP-negative (Con) cells were analyzed separately. (C) The downregulation of c-Myc by Aiolos and Ikaros is independent of p27. The expression of c-Myc was examined by using mRNA isolated from the Aiolos- and Ikaros-infected p27+/+ and p27−/− pre-B cells (described in Fig. 5B). (D) Downregulation of cyclin D3 by Aiolos and Ikaros is compromised in p27−/− pre-B cells. The expression of cyclin D3 was examined by using mRNA isolated from the Aiolos- and Ikaros-infected p27+/+ and p27−/− pre-B cells (described in Fig. 5B). (E and F) Sustained c-Myc expression blocks IL-7 withdrawal induced cell cycle arrest and prevents p27 induction and cyclin D3 downregulation. Wild-type (Wt), DKO, and Eμ-Myc pre-B cells were cultivated in the presence or absence of IL-7 for 24 h and then lysed for Western blot analysis with antibodies against indicated proteins (E). The cell cycle status of the cells was also analyzed by FACS (F). The result is representative of at least three independent experiments. The statistical significance was determined by a Student t test (*, P < 0.05; **, P < 0.01).