AUTHOR=Padder Rayees Ahmad , Bhat Zafar Iqbal , Ahmad Zaki , Singh Neetu , Husain Mohammad 

TITLE=DRP1 Promotes BRAFV600E-Driven Tumor Progression and Metabolic Reprogramming in Colorectal Cancer

JOURNAL=Frontiers in Oncology

VOLUME=10

YEAR=2021

URL=https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2020.592130

DOI=10.3389/fonc.2020.592130

ISSN=2234-943X

ABSTRACT=<sec><title>Background</title><p>Mitochondria are highly dynamic organelles which remain in a continuous state of fission/ fusion dynamics to meet the metabolic needs of a cell. However, this fission/fusion dynamism has been reported to be dysregulated in most cancers. Such enhanced mitochondrial fission is demonstrated to be positively regulated by some activating oncogenic mutations; such as those of KRAS (Kristen rat sarcoma viral oncogene homologue) or BRAF (B- rapidly accelerated fibrosarcoma), thereby increasing tumor progression/ chemotherapeutic resistance and metabolic deregulation. However, the underlying mechanism(s) are still not clear, thus highlighting the need to further explore possible mechanism(s) of intervention. We sought to investigate how BRAF<sup>V600E</sup> driven CRC (colorectal cancer) progression is linked to mitochondrial fission/fusion dynamics and whether this window could be exploited to target CRC progression.</p></sec><sec><title>Methods</title><p>Western blotting was employed to study the differences in expression levels of key proteins regulating mitochondrial dynamics, which was further confirmed by confocal microscopy imaging of mitochondria in endogenously expressing <bold>BRAF<sup>WT</sup></bold> and <bold>BRAF<sup>V600E</sup></bold> CRC cells. Proliferation assays, soft agar clonogenic assays, glucose uptake/lactate production, ATP/ NADPH measurement assays were employed to study the extent of carcinogenesis and metabolic reprograming in <bold>BRAF<sup>V600E</sup></bold> CRC cells. Genetic knockdown (shRNA/ siRNA) and/or pharmacologic inhibition of Dynamin related protein1/Pyruvate dehydrogenase kinase1 (DRP1/PDK1) and/or BRAF<sup>V600E</sup> were employed to study the involvement and possible mechanism of these proteins in <bold>BRAF<sup>V600E</sup></bold> driven CRC. Statistical analyses were carried out using Graph Pad Prism v 5.0, data was analyzed by unpaired t-test and two-way ANOVA with appropriate post hoc tests.</p></sec><sec><title>Results</title><p>Our results demonstrate that <bold>BRAF<sup>V600E</sup></bold> CRC cells have higher protein levels of mitochondrial fission factor- <bold>DRP1/pDRP1<sup>S616</sup></bold> leading to a more fragmented mitochondrial state compared to those harboring <bold>BRAF<sup>WT</sup></bold>. This fragmented mitochondrial state was found to confer glycolytic phenotype, clonogenic potential and metastatic advantage to cells harboring <bold>BRAF<sup>V600E</sup></bold>. Interestingly, such fragmented mitochondrial state seemed positively regulated by mitochondrial <bold>PDK1</bold> as observed through pharmacologic as well as genetic inhibition of <bold>PDK1</bold>.</p></sec><sec><title>Conclusion</title><p>In conclusion, our data suggest that <bold>BRAF<sup>V600E</sup></bold> driven colorectal cancers have fragmented mitochondria which confers glycolytic phenotype and growth advantage to these tumors, and such phenotype is dependent at least in part on <bold>PDK1</bold>- thus highlighting a potential therapeutic target.</p></sec>