Pyruvate dehydrogenase E1 alpha (PDHE1α or PDHA1) is the first component enzyme of the pyruvate dehydrogenase (PDH) complex (PDC) that transforms pyruvate, via pyruvate decarboxylation, into acetyl-CoA that is subsequently used by both the citric acid cycle and oxidative phosphorylation to generate ATP. As such, PDH links glycolysis and oxidative phosphorylation in normal as well as cancer cells. Herein we report that SIRT3 interacts with PDHA1 and directs its enzymatic activity via changes in protein acetylation. SIRT3 deacetylates PDHA1 lysine 321 (K321) and a PDHA1 mutant, mimicking a deacetylated lysine (PDHA1K321R) increases in PDH activity, as compared to the K321 acetylation mimic (PDHA1K321Q) or wild-type PDHA1. Finally, PDHA1K321Q exhibited a more transformed in vitro cellular phenotype as compared to PDHA1K321R. These results suggest that the acetylation of PDHA1 provides another layer of enzymatic regulation, in addition to phosphorylation, involving a reversible acetyl-lysine suggesting that the acetylome, as well as the kinome, links glycolysis to respiration.

The efficacy of monoclonal antibodies (mAbs) used to treat solid tumors is limited by intercellular junctions which tightly link epithelial tumor cells to each another. In this study, we define a small, recombinant adenovirus serotype 3-derived protein, termed junction opener 1 (JO-1), which binds to the epithelial junction protein desmoglein 2 (DSG2). In mouse xenograft models employing Her2/neu- and EGFR-positive human cancer cell lines, JO-1 mediated cleavage of DSG2 dimers and activated intracellular signaling pathways which reduced E-cadherin expression in tight junctions. Notably, JO-1-triggered changes allowed for increased intratumoral penetration of the anti-Her2/neu mAb trastuzumab (Herceptin) as well as improved access to its target receptor, Her2/neu, which is partly trapped in tight junctions. This effect translated directly into increased therapeutic efficacy of trastuzumab in mouse xenograft models using breast, gastric, and ovarian cancer cells that were Her2/neu-positive. Furthermore, combining JO-1 with the EGFR-targeting mAb cetuximab (Erbitux) greatly improved therapeutic outcomes in a metastatic model of EGFR-positive lung cancer. Taken together, our findings offer preclinical proof of concept to employ JO-1 in combination treatments which enhance the efficacy of trastuzumab treatment, by generating a transient degradation of tumor stroma proteins that can elicit eradication of tumors.