HoxC4 binds to the promoter of the cytidine deaminase AID gene to induce AID expression, class-switch DNA recombination and somatic hypermutation


The cytidine deaminase AID (encoded by Aicda in mice and AICDA in humans) is critical for immunoglobulin class-switch recombination (CSR) and somatic hypermutation (SHM). Here we show that AID expression was induced by the HoxC4 homeodomain transcription factor, which bound to a highly conserved HoxC4-Oct site in the Aicda or AICDA promoter. This site functioned in synergy with a conserved binding site for the transcription factors Sp1, Sp3 and NF-κB. HoxC4 was 'preferentially' expressed in germinal center B cells and was upregulated by engagement of CD40 by CD154, as well as by lipopolysaccharide and interleukin 4. HoxC4 deficiency resulted in impaired CSR and SHM because of lower AID expression and not some other putative HoxC4-dependent activity. Enforced expression of AID in Hoxc4−/− B cells fully restored CSR. Thus, HoxC4 directly activates the Aicda promoter, thereby inducing AID expression, CSR and SHM.

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Figure 1: Hoxc4 expression correlates with Aicda expression.
Figure 2: Impaired antibody response in Hoxc4−/− mice.
Figure 3: HoxC4 deficiency does not affect B cell, T cell or CD4+ T cell numbers, death of B cells and T cells in spleens and Peyer's patches or B cell cycle or division or alter germinal center formation and in vivo B cell proliferation.
Figure 4: Impaired CSR in Hoxc4−/− B cells.
Figure 5: HoxC4 deficiency does not alter germline IH-CH transcripts but results in lower expression of post-recombination Iμ-CH transcripts.
Figure 6: Somatic mutation in the immunoglobulin heavy-chain intronic JH4-iEμ DNA of Peyer's patch PNAhiB220+ (germinal center) B cells.
Figure 7: HoxC4 deficiency impairs AID expression, which depends on the conserved HoxC4-Oct–binding site in the Aicda promoter.
Figure 8: The conserved HoxC4-Oct– and Sp–NF-κB–binding sites are essential for full Aicda promoter activity, and HoxC4, Oct1, Oct2, Oca-B, Pax5, Sp1, Sp3 and NF-κB (p52) are recruited to the Aicda promoter in B cells expressing AICDA or Aicda and undergoing CSR or SHM.
Figure 9: Enforced expression of AID restores CSR in Hoxc4−/− B cells.


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We thank M.R. Capecchi and A.M. Boulet (University of Utah) for Hoxc4+/− frozen mouse sperm; T. Fielder for technical efforts; L. Khidr, L. Phan, B. Gupta, J. Feng and Y. Zhong for handling Hoxc4+/− mice; C. Murre (University of California, San Diego) for the Aicda retroviral construct, T. Honjo (Kyoto University) for CH12F3-2A cells; C.M. Snapper (Uniformed Services University of the Health Sciences) for dextran-conjugated mAb to δ-chain; Z. Yu for statistic analysis; A. Schaffer for discussions; and S. Sabet and M. Kang for technical assistance. Supported by the US National Institutes of Health (AI 045011, AI 079705 and AI 060573 to P.C.).

Author information

S.-R.P., H.Z., Z.P., J.Z., A.A.-Q., E.J.P., Z.X. and T.M. did experiments; H.Z. designed experiments, analyzed data and prepared the manuscript; and P.C. designed all experiments, analyzed the data, supervised the work and prepared the manuscript.

Correspondence to Paolo Casali.

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Park, S., Zan, H., Pal, Z. et al. HoxC4 binds to the promoter of the cytidine deaminase AID gene to induce AID expression, class-switch DNA recombination and somatic hypermutation. Nat Immunol 10, 540–550 (2009) doi:10.1038/ni.1725

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