Carnosol Is a Novel Inhibitor of p300 Acetyltransferase in Breast Cancer

Abstract

Carnosol, a natural polyphenol abundant in edible plants such as sage, rosemary, and oregano, has shown promising anticancer activity against various types of cancers. Nonetheless, very little is known about its molecular mechanism of action or its downstream target(s). We have previously shown that carnosol inhibits cellular proliferation, migration, invasion, and metastasis as well as triggers autophagy and apoptosis in the highly invasive MDA-MB-231 breast cancer cells. Here, we report that carnosol induces histone hypoacetylation in MDA-MB-231 and Hs578T breast cancer cells. We show that, while carnosol does not affect HDACs, it promotes a ROS-dependent proteasome degradation of p300 and PCAF histone acetyl transferases (HATs) without affecting other HATs such as GCN5 and hMOF. Carnosol-induced histone hypoacetylation remains persistent even when p300 and PCAF protein levels were rescued from degradation by (i) the inhibition of the proteasome activity by the proteasome inhibitors MG-132 and bortezomib, and (ii) the inhibition of ROS accumulation by the ROS scavenger, N-acetylcysteine. In addition, we report that, in a cell-free system, carnosol efficiently inhibits histone acetyltransferase activity of recombinant p300 but not that of PCAF or GCN5. Molecular docking studies reveal that carnosol inhibits p300 HAT activity by blocking the entry of the acetyl-CoA binding pocket of the catalytic domain. The superimposition of the docked conformation of the p300 HAT domain in complex with carnosol shows a similar orientation as the p300 structure with acetyl-CoA. Carnosol occupies the region where the pantetheine arm of the acetyl-CoA is bound. This study further confirms carnosol as a promising anti-breast cancer therapeutic compound and identifies it as a novel natural p300 inhibitor that could be added to the existing panel of inhibitors.

Carnosol Induces p38-Mediated ER Stress Response and Autophagy in Human Breast Cancer Cells

“…An increase in the overall protein polyubiquitination was as well as mTOR degradation was detectable as early as 3 hours post-carnosol treatment ( Figure 7C ). Because we had previously shown that carnosol also induced a proteasome degradation of STAT3 ( 31 )as well as p300 ( 34 )and PCAF ( 34 ) histone acetyltransferases, we decided to determine the time at which this degradation occurs. As shown in Figure 7C , similar to mTOR’s, PCAF degradation was detected as early as 3 hours post-treatment.…”

“…We also reported that carnosol induces ROS-mediated beclin1-independent autophagy and apoptosis in triple-negative breast cancer ( 30 ). More recently, we showed that carnosol selectively inhibits the p300 histone acetyl transferase in breast cancer cells ( 34 ). Here, we show that carnosol triggers a ROS-dependent ER-stress response through activation of the three ER stress sensor pathways in breast cancer cells.…”

Advances of Epigenetic Biomarkers and Epigenome Editing for Early Diagnosis in Breast Cancer

“…EP300 is one of the most studied HATs, encoded by the E1A binding protein P300 ( EP300 ) gene which mediates histone and non-histone protein acetylation, and it is involved in gene activation [ 46 , 107 ]. Moreover, high expression and activity of EP300 was demonstrated to be associated with various diseases and malignancies, including pulmonary fibrosis [ 46 ], nasopharyngeal carcinoma (NPC) [ 108 ], hepatocellular carcinoma (HCC) [ 109 ], non-small cell lung cancers (NSCLC) [ 110 ], prostate cancer (PCa) [ 111 ], and breast cancer (BC) [ 112 ]. Moreover, EP300 is associated with several neurodegenerative disorders [ 113 ].…”

“…Mice expressing a truncated EP300 protein in the hippocampus, amygdala, cortex, and cerebellum were shown to have memory deficits in contextual fear conditioning and object recognition tasks [ 114 ]. Additionally, knockdown and pharmacological inhibition of EP300 were shown to reduce tumor growth and metastasis in vitro and in a xenograft mouse model of BC in vivo [ 112 , 115 ]. In addition to EP300, GCN5 is another family member of HATs that was found to play a key role in the TGF-β/SMAD signaling pathway in breast cancer cells [ 116 ].…”

Histone modification and histone modification-targeted anti-cancer drugs in breast cancer: Fundamentals and beyond

“…Carnosol, which takes the region binding acetyl-CoA’s pantetheine arm, is verified to be the candidate anti-BC target. In addition, it is the new natural p300 inhibitor, which can be listed in the current inhibitor panel ( Alsamri et al, 2021 ).…”