CBX7 is a tumor suppressor in mice and humans
Floriana Forzati, … , Monica Fedele, Alfredo Fusco
Floriana Forzati, … , Monica Fedele, Alfredo Fusco
Published January 3, 2012
Citation Information: J Clin Invest. 2012;122(2):612-623. https://doi.org/10.1172/JCI58620.
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Research Article Oncology

CBX7 is a tumor suppressor in mice and humans

Abstract

The CBX7 gene encodes a polycomb group protein that is known to be downregulated in many types of human cancers, although the role of this protein in carcinogenesis remains unclear. To shed light on this issue, we generated mice null for Cbx7. Mouse embryonic fibroblasts derived from these mice had a higher growth rate and reduced susceptibility to senescence compared with their WT counterparts. This was associated with upregulated expression of multiple cell cycle components, including cyclin E, which is known to play a key role in lung carcinogenesis in humans. Adult Cbx7-KO mice developed liver and lung adenomas and carcinomas. In in vivo and in vitro experiments, we demonstrated that CBX7 bound to the CCNE1 promoter in a complex that included HDAC2 and negatively regulated CCNE1 expression. Finally, we found that the lack of CBX7 protein expression in human lung carcinomas correlated with CCNE1 overexpression. These data suggest that CBX7 is a tumor suppressor and that its loss plays a key role in the pathogenesis of cancer.

Authors

Floriana Forzati, Antonella Federico, Pierlorenzo Pallante, Adele Abbate, Francesco Esposito, Umberto Malapelle, Romina Sepe, Giuseppe Palma, Giancarlo Troncone, Marzia Scarfò, Claudio Arra, Monica Fedele, Alfredo Fusco

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Figure 5

Competition between HMGA1 and CBX7 for binding, regulation, and acetylation of the CCNE1 promoter.

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Competition between HMGA1 and CBX7 for binding, regulation, and acetylat...
(A) ChIP and re-ChIP assay, revealed by qRT-PCR, on HEK 293 cells transfected with HMGA1b expression vector, HA-tagged CBX7 expression vector, or both to detect the HMGA1/CBX7, CBX7/HDAC2, and HMGA1/HDAC2 interactions on the CCNE1 promoter. GAPDH promoter was also analyzed as a negative control. (B) Percent HDAC2 protein co-IP with HMGA1, as detected in the ChIP and re-ChIP assay in A, comparatively reported in cells transfected with HMGA1b with or without CBX7. **P < 0.01. (C) EMSA, performed as in Figure 3B, using 5 ng GST-CBX7 (lanes 4–8) and 5 and 20 ng His-HMGA1b (lanes 1–3 and 6–8). A 400-fold molar excess of unlabeled probe (lanes 3, 5, and 8) was added as a specific competitor, and 5 ng of a recombinant GST protein (lane 9) was used as a negative control. (D) CCNE1 promoter–driven luciferase activity, expressed relative to activation of empty vector–transfected cells, in HEK 293 cells. Where indicated, 1 μg CBX7 and/or 1, 2, and 5 μg HMGA1b expression vectors were cotransfected with the cyclin E–luc plasmid. (E) ChIP assay, revealed by qRT-PCR, on HEK 293 cells transfected with CBX7 expression vector, HMGA1b expression vector, both, or empty vector for binding of acetylated histone H4 (AcH4) to the CCNE1 promoter. Equal amounts of proteins were subjected to IP with anti-AcH4 antibodies or nonspecific IgG, as indicated.