CBX2 and CBX7 antagonistically regulate metabolic reprogramming in breast cancer

Striking similarity exists between metabolic changes associated with embryogenesis and tumorigenesis. Chromobox proteins-CBX2/4/6/7/8, core components of canonical polycomb repressor complex 1 (cPRC1), play essential roles in embryonic development and aberrantly expressed in breast cancer. Understanding how altered CBX expression relates to metabolic reprogramming in breast cancer may reveal vulnerabilities of therapeutic pertinence. Using transcriptomic and metabolomic data from breast cancer patients (N>3000 combined), we identified outstanding roles of CBX2 and CBX7 in positive and negative regulation of glucose metabolism, respectively. Genetic ablation experiments validated the contrasting roles of two isoforms in cancer metabolism and cell growth. Furthermore, we determined that contrary effects of CBX2 and CBX7 on breast cancer metabolism were due to differential modulation of the mTORC1 signaling by two isoforms. Underpinning the biological significance of metabolic roles, CBX2 and CBX7 were found to be the most up- and down-regulated isoforms, respectively, in breast tumors compared to normal tissues. Moreover, CBX2 and CBX7 expression (not other isoforms) correlated strongly, but oppositely, with breast tumor aggressiveness. Genomic data showed higher amplification frequency of CBX2, not CBX7, in breast tumors. Highlighting the clinical significance of findings, survival and drug sensitivity analysis revealed that CBX2 and CBX7 predicted patient outcome and sensitivity to clinical drugs. In summary, this work identifies previously unknown antagonistic roles of CBX2 and CBX7 in breast tumor metabolism, and the results presented may have implications in strategies targeting breast cancer metabolism. Significance statementMetabolic reprogramming is a hallmark of cancer. Understanding how reprogramming of metabolism is regulated in cancer may reveal therapeutically relevant targets. Using integrative approach, we elucidate the hitherto unknown antagonistic roles of CBX2 and CBX7 in breast cancer metabolism. Highlighting the relevance of identified metabolic roles, we found that CBX2 and CBX7 (not other members) are the most differentially expressed isoforms in breast tumors (compared to normals) and the only isoforms which significantly correlate with breast cancer aggressiveness. Further, CBX2/7 predicted patient outcome and response to drugs used in breast cancer treatment, underscoring clinical significance of our study. In brief, this work unravels novel metabolic roles of CBX2/7 which may have implications in breast cancer treatment.