miR-155 is positively regulated by CBX7 in MEFs and colon carcinomas, and has KRAS as one of the target genes likely accounting for the anti-apoptotic activity ascribed to miR-155 in some tissue contexts.
Since CBX7 is drastically downregulated in human lung carcinomas, we investigated whether restoration of CBX7 expression could affect growth property of lung cancer cells and modulate their sensitivity to treatment with irinotecan and etoposide, two chemoterapy drugs most commonly used in lung cancer therapy.
Several recent studies have reported the Polycomb Repressive Complex 1 member CBX7 as a tumor-suppressor gene whose expression progressively decreases in different human carcinomas in relation with tumor grade, malignant stage and poor prognosis.
The Alu-normalized Cbx7 mRNA levels were significantly increased in SM tissues when compared with CC tissues or colon biopsies taken from non-cancer patients (Student's t-test, P < 0.036 or 0.007).
A similar mechanism is likely involved in human lung carcinogenesis, since cyclin E upregulation associated with the loss of CBX7 expression has been observed in most of the human lung carcinomas analyzed.