Abstract 1967: Chaperonin-Containing TCP1 complex (CCT) promotes breast cancer by targeting key cell cycle regulators

CCT is a protein folding complex that interacts with known oncoproteins, but its role as a driver of oncogenesis is unknown. Elucidating interactions of CCT with cell cycle regulators could reveal the oncogenic potential of the chaperonin. CCT is multi-subunit complex composed of two stacked rings formed by eight distinct subunits (CCT1-8). While different CCT subunits are associated with cancer and other diseases, we found that the CCT2 subunit is upregulated in breast cancer and other cancers and that its expression inversely correlates with patients' overall and progression free survival. Mining datasets from TCGA revealed that amplification of CCT2 is the predominant genomic alteration occurring in cancer patients and that CCT2 is frequently co-amplified or co-expressed with other oncogenes such as MDM2, FRS2, YEATS4, and CDK4 found in the 12q13-15 amplicon. Genetic alteration of CCT2 significantly associates with worse clinical outcome for cancer patients. To investigate the functional outcomes of CCT2 overexpression in breast cancer, spheroid culture was used. A CCT2-FLAG lentiviral vector was used to transduce T47D and MCF7 luminal breast cancer cells and cells grown in ultra-low attachment plates to induce spheroid growth. Expression of CCT2 increased growth of spheroids as compared to lentiviral control cells. In contrast, CCT2 depletion impaired spheroid formation, instead causing formation of loose aggregates. CCT2 overexpression increased the proliferative potential of spheroid cells and promoted progression though the G1/S phase of the cell cycle in synchronized cells by increasing expression of cell cycle regulators like Cyclin D1, CDK2 and CDK4. After 8 days in spheroid culture, CCT2 overexpressing cancer cells resumed attachment when transferred into 2D culture conditions; these cells acquire anchorage dependent and independent growth capability, increased actin expression, and proliferated. These characteristics of CCT2 overexpressing cells may be indicative of supporting a more invasive and metastatic phenotype. In support, we discovered that, along with cell cycle genes, CCT2 overexpressed cells increased expression of MYC, suggesting the CCT2 could be a novel regulator of MYC expression. Our results contribute new knowledge on the role of CCT2 in uncontrolled breast cancer progression and proliferation by regulating cell cycle genes. The recurrent amplification of CCT2 in different cancer types along with other oncogenes like MYC, MDM2