Mitochondrial Division Is Requisite to RAS-Induced Transformation and Targeted by Oncogenic MAPK Pathway Inhibitors

Abstract

SUMMARY Mitochondrial division is essential for mitosis and metazoan development, but a mechanistic role in cancer biology remains unknown. Here, we examine the direct effects of oncogenic RASG12V mediated cellular transformation on the mitochondrial dynamics machinery and observe a positive selection for dynamin related protein 1 (DRP1), a protein required for mitochondrial network division. Loss of DRP1 prevents RASG12V-induced mitochondrial dysfunction, and renders cells resistant to transformation. Conversely, in human tumor cell lines with activating MAPK mutations, inhibition of these signals leads to robust mitochondrial network reprogramming initiated by DRP1 loss resulting in mitochondrial hyper-fusion and increased mitochondrial metabolism. These phenotypes are mechanistically linked by ERK1/2 phosphorylation of DRP1 serine 616; DRP1S616 phosphorylation is sufficient to phenocopy transformation-induced mitochondrial dysfunction, and DRP1S616 phosphorylation status dichotomizes BRAFWt from BRAFV600E positive lesions. These findings implicate mitochondrial division and DRP1 as crucial regulators of transformation with unexpected leverage in chemotherapeutic success.

A novel mitochondrial pool of Cyclin E, regulated by Drp1, is linked to cell density dependent cell proliferation

“…Recently, Ras-driven MEK-ERK signaling has been shown to activate Drp1-dependent mitochondrial fission (Serasinghe et al, 2015;Kashatus et al, 2015) in line with our previous finding that EGFR signaling (mediated by downstream activation of MEK-ERK signaling) promotes mitochondrial fission (Mitra et al, 2012). We have further shown that loss of Drp1-driven mitochondrial fission aberrantly enhances EGFR signaling to support aberrant cell proliferation (Mitra et al, 2012).…”

“…3C). Such boosted mitochondrial energetics in the absence of DRP1 has also been found in other mouse and human cells (Serasinghe et al, 2015;Kashatus et al, 2015). Furthermore, we found that the enhanced spare respiratory capacity between the DRP1-KO and WT MEFs was abrogated after 2 h of serum depletion, whereas both WT and DRP1-KO MEFs had enhanced spare respiratory capacity in the presence of serum (Fig.…”

“…Our study, based on DRP1-KO MEFs that are immortalized (using SV-40T antigens) (Ishihara et al, 2009) and a Drosophila model system, predicts that lowering of Drp1 activity would prevent oncogenic Ras-driven transformation at low cell densities because Ras-driven MEK-ERK signaling would fail to release mtCycE for degradation. Indeed, recent reports attempting to transform cells in the absence of Drp1 (using combinations of transforming agents; Kashatus et al, 2015;Serasinghe et al, 2015) have demonstrated that Ras-driven transformation is attenuated when Drp1 is lowered. However, Ras-driven MEK-ERK signaling in cells with reduced Drp1 at high cell densities would release mtCycE to support aberrant cell proliferation and possibly lead to cell transformation.…”

Mitochondrial dynamics and cancer

“…49,60 In agreement with the previous observations, it has also been reported that several cancer cell lines or cells that have been transformed with oncogenes have more fragmented mitochondria than their non-transformed controls. 48,55,56,59 At least one of the molecular mechanisms involved in the maintenance of fragmented mitochondria in cancer cells has been recently elucidated and it has been proposed to involve the MAPK signaling pathway, a proliferation pathway activated in a variety of tumors. In normal cells, the RAS-RAF-MEK-ERK (MAPK) pathway is activated by growth factors and hormone signaling and its precise regulation controls proliferation and cell death.…”

The mitochondrial dynamics in cancer and immune-surveillance

“…Interestingly, the oncogenic MAPK/ERK pathway, which is a driver of cancer progression in different tumors, is able to upregulate Drp1 activity in different cancers [147,148] by phosphorylation on serine residue Ser616 [147]. In several human cancers, a poor survival rate is associated with an increased Drp1 level [54,67,70,71,144,149] or a decreased Mfn-2 [150,151] or Mfn-1 amounts [144,152], as also confirmed by the emerging Bioinformatics databases displaying the expression levels of different mitochondria-shaping proteins in human tumors (see The Human Atlas Project [153] and Table 1 for details).…”