CTCF and BORIS regulate Rb2/p130 gene transcription: a novel mechanism and a new paradigm for understanding the biology of lung cancer.

Although innumerable investigations regarding the biology of lung cancer have been carried out, many aspects thereof remain to be addressed, including the role played by the retinoblastoma-related protein Rb2/p130 during the evolution of this disease. Here we report novel findings on the mechanisms that control Rb2/p130 gene expression in lung fibroblasts and characterize the effects of Rb2/p130 deregulation on the proliferative features of lung cancer cells. We revealed for the first time that in lung fibroblasts the expression of Rb2/p130 gene is directly controlled by the chromatin insulator CCCTC-binding factor, CTCF, which by binding to the Rb2/p130 gene promoter induces, and/or maintains, a specific local chromatin organization that in turn governs the transcriptional activity of Rb2/p130 gene. However, in lung cancer cells the activity of CTCF in controlling Rb2/p130 gene expression is impaired by BORIS, a CTCF-paralogue, which by binding to the Rb2/p130 gene could trigger changes in the chromatin asset established by CTCF, thereby affecting CTCF regulatory activity on Rb2/p130 transcription. These studies not only provide essential basic insights into the molecular mechanisms that control Rb2/p130 gene expression in lung cancer, but also offer a potential paradigm for the actions of other activators and/or corepressors, such as CTCF and BORIS, that could be crucial in explaining how alterations in the mechanism regulating Rb2/p130 gene expression may accelerate the progression of lung tumors, or favor the onset of recurrence after cancer treatment.