Background Mammalian cells must constantly reprogram the distribution of mitochondria in order to meet the local demands for energy, calcium, redox balance, and other mitochondrial functions. Mitochondrial localization inside the cell is a result of a combination of movement along the microtubule tracks plus anchoring to actin filaments. Recent findings Recent advances show that subcellular distribution of mitochondria can regulate tumor cell growth, proliferation/motility plasticity, metastatic competence, and therapy responses in tumors. In this review, we discuss our current understanding of the mechanisms by which mitochondrial subcellular distribution is regulated in tumor cells. Conclusions Mitochondrial trafficking is dysregulated in tumors. Accumulation of mitochondria at the leading edge of the cell supports energy expensive processes of focal adhesion dynamics, cell membrane dynamics, migration, and invasion.

There is a continued need to identify novel therapeutic targets to prevent the mortality associated with prostate cancer. In this context, Mitochondrial Rho GTPase 2 (MIRO2) mRNA was upregulated in metastatic prostate cancer compared to localized tumors, and higher MIRO2 levels were correlated with poor patient survival. Using human cell lines that represent androgen-independent or -sensitive prostate cancer, we showed that MIRO2 depletion impaired cell growth, colony formation and tumor growth in mice. Network analysis of MIRO2's binding partners identified metabolism and cellular responses to extracellular stimuli as top over-represented pathways. The top hit on our screen, General Control Nonderepressible 1 (GCN1), was overexpressed in prostate cancer, and interacted with MIRO2 in prostate cancer cell lines and in primary prostate cancer cells. Functional analysis of MIRO2 mutations present in prostate cancer patients led to the identification of MIRO2 159L, which increased GCN1 binding.Importantly, MIRO2 was necessary for efficient GCN1-mediated GCN2 kinase signaling and induction of the transcription factor ATF4 levels. Further, MIRO2's effect on regulating prostate cancer cell growth was mediated by ATF4. Finally, levels of activated GCN2 and ATF4 were correlated with MIRO2 expression in prostate cancer xenografts. Both MIRO2 and activated GCN2 levels were higher in hypoxic areas of prostate cancer xenografts. Overall, we propose that targeting the MIRO2-GCN1 axis may be a valuable strategy to halt prostate cancer growth.Implications: MIRO2/GCN1/GCN2 constitute a novel mitochondrial signaling pathway that controls androgen-independent and androgen-sensitive prostate cancer cell growth.

Mating-types allow single-celled eukaryotic organisms to distinguish self from non-self in preparation for sexual reproduction. The components of mating-type loci provide initial self/non-self-recognition through pheromone and receptor interactions that control early cell fusion events. However, they may also provide a second level of scrutiny that requires differences in alleles leading to production of a transcription factor required for successful downstream developmental pathways after initial cell fusion. Interestingly, the protein subunits of these transcription factors have not been thoroughly examined for their roles, if any, in the haploid cells themselves. In Ustilago maydis, the causative agent of galls in maize plants, the b locus, encoding bEast (bE) and bWest (bW), components of the eventual requisite transcription factor, has been extensively studied for its role in formation of the stable dikaryon after mating and subsequent pathogenic program. Little is known, however, about any roles for bE or bW in haploid cells. Since mating in fungi is often induced under conditions of nitrogen starvation, we have explored connections between the b locus and the nitrogen-sensing and response pathways in U. maydis. We previously identified a connection in haploid cells between the b locus and Ump2, the high-affinity transceptor, a protein that both transports ammonium and triggers filamentous growth as a response to nitrogen starvation. Deletion of the entire b locus abrogates the filamentous response to low ammonium, a phenotype that is rescued by overexpression of Ump2. Here we further investigated the individual roles of bE and bW in haploid cells. We show that bE and bW are expressed differentially in haploid cells starved for ammonium. Their respective deletion elicits different effects on transcription of mating and pathogenic-related genes and, importantly, on the degree of pathogenic development in host plants. This is the first demonstration of a role for these mating locus components on haploid development and the first to demonstrate a connection to the ammonium transceptors.

There is a continued need to identify novel therapeutic targets to prevent the mortality associated with prostate cancer. In this context, we discovered a novel mitochondrial signaling pathway that controls androgen-independent and androgen-sensitive prostate cancer cell growth. Mitochondrial Rho GTPase 2 (MIRO2) mRNA was upregulated in prostate cancer compared to localized tumors, and higher MIRO2 levels were correlated with poor patient survival. Using human cell lines that represent AR-independent or androgen-sensitive prostate cancer, we show that MIRO2 depletion impaired cell growth, colony formation and tumor growth in mice. Network analysis of MIRO2's binding partners identified metabolism, cell cycle, and cellular responses to extracellular stimuli amongst the top over-represented pathways. The top hit on our screen was General Control Non-derepressible 1 (GCN1). GCN1 was overexpressed in prostate cancer and MIRO2-GCN1 interacted in prostate cancer cell lines and in primary prostate cancer cells. Our results showed that MIRO2 is necessary for efficient GCN1-mediated GCN2 kinase activation and signaling, triggering translation of the transcription factor ATF4. Importantly, MIRO2 controlled ATF4 levels and transcriptional activity both in amino acid replete and depleted conditions. Furthermore, MIRO2's effect on regulating prostate cancer cell growth was partially mediated by ATF4. Finally, activation of GCN2 and ATF4 expression were correlated with MIRO2 expression in prostate cancer xenografts. Overall, we propose a new mechanism driving prostate cancer growth of both AR-independent and androgen-sensitive tumors.

Supplementary Figure from MIRO2 Regulates Prostate Cancer Cell Growth via GCN1-Dependent Stress Signaling

<div>Abstract<p>There is a continued need to identify novel therapeutic targets to prevent the mortality associated with prostate cancer. In this context, mitochondrial Rho GTPase 2 (<i>MIRO2</i>) mRNA was upregulated in metastatic prostate cancer compared with localized tumors, and higher <i>MIRO2</i> levels were correlated with poor patient survival. Using human cell lines that represent androgen-independent or -sensitive prostate cancer, we showed that MIRO2 depletion impaired cell growth, colony formation, and tumor growth in mice. Network analysis of MIRO2′s binding partners identified metabolism and cellular responses to extracellular stimuli as top overrepresented pathways. The top hit on our screen, General Control Nonderepressible 1 (GCN1), was overexpressed in prostate cancer, and interacted with MIRO2 in prostate cancer cell lines and in primary prostate cancer cells. Functional analysis of MIRO2 mutations present in patients with prostate cancer led to the identification of MIRO2 159L, which increased GCN1 binding. Importantly, MIRO2 was necessary for efficient GCN1-mediated GCN2 kinase signaling and induction of the transcription factor activating transcription factor 4 (ATF4) levels. Further, MIRO2′s effect on regulating prostate cancer cell growth was mediated by ATF4. Finally, levels of activated GCN2 and ATF4 were correlated with MIRO2 expression in prostate cancer xenografts. Both MIRO2 and activated GCN2 levels were higher in hypoxic areas of prostate cancer xenografts. Overall, we propose that targeting the MIRO2-GCN1 axis may be a valuable strategy to halt prostate cancer growth.</p>Implications:<p>MIRO2/GCN1/GCN2 constitute a novel mitochondrial signaling pathway that controls androgen-independent and androgen-sensitive prostate cancer cell growth.</p></div>

Supplementary Table from MIRO2 Regulates Prostate Cancer Cell Growth via GCN1-Dependent Stress Signaling

Supplementary Table from MIRO2 Regulates Prostate Cancer Cell Growth via GCN1-Dependent Stress Signaling