Syntaphilin controls a mitochondrial rheostat for proliferation-motility decisions in cancer.

Tumors adapt to an unfavorable microenvironment by controlling the balance between cell proliferation and cell motility, but the regulators of this process are largely unknown. Here, we show that an alternatively spliced isoform of syntaphilin (SNPH), a cytoskeletal regulator of mitochondrial movements in neurons, is directed to mitochondria of tumor cells. Mitochondrial SNPH buffers oxidative stress and maintains complex II-dependent bioenergetics, sustaining local tumor growth while restricting mitochondrial redistribution to the cortical cytoskeleton and tumor cell motility. Conversely, introduction of stress stimuli to the microenvironment, including hypoxia, acutely lowered SNPH levels, resulting in bioenergetics defects and increased superoxide production. In turn, this suppressed tumor cell proliferation but increased tumor cell invasion via greater mitochondrial trafficking to the cortical cytoskeleton. Loss of SNPH or expression of an SNPH mutant lacking the mitochondrial localization sequence resulted in increased metastatic dissemination in xenograft or syngeneic tumor models in vivo. Accordingly, tumor cells that acquired the ability to metastasize in vivo constitutively downregulated SNPH and exhibited higher oxidative stress, reduced cell proliferation, and increased cell motility. Therefore, SNPH is a stress-regulated mitochondrial switch of the cell proliferation-motility balance in cancer, and its pathway may represent a therapeutic target

Obesity Is Associated with Altered Tumor Metabolism in Metastatic Melanoma

PURPOSE: Overweight/obese (OW/OB) patients with metastatic melanoma unexpectedly have improved outcomes with immune checkpoint inhibitors (ICI) and BRAF-targeted therapies. The mechanism(s) underlying this association remain unclear, thus we assessed the integrated molecular, metabolic, and immune profile of tumors, as well as gut microbiome features, for associations with patient body mass index (BMI). EXPERIMENTAL DESIGN: Associations between BMI [normal (NL \u3c 25) or OW/OB (BMI ≥ 25)] and tumor or microbiome characteristics were examined in specimens from 782 patients with metastatic melanoma across 7 cohorts. DNA associations were evaluated in The Cancer Genome Atlas cohort. RNA sequencing from 4 cohorts (n = 357) was batch corrected and gene set enrichment analysis (GSEA) by BMI category was performed. Metabolic profiling was conducted in a subset of patients (x = 36) by LC/MS, and in flow-sorted melanoma tumor cells (x = 37) and patient-derived melanoma cell lines (x = 17) using the Seahorse XF assay. Gut microbiome features were examined in an independent cohort (n = 371). RESULTS: DNA mutations and copy number variations were not associated with BMI. GSEA demonstrated that tumors from OW/OB patients were metabolically quiescent, with downregulation of oxidative phosphorylation and multiple other metabolic pathways. Direct metabolite analysis and functional metabolic profiling confirmed decreased central carbon metabolism in OW/OB metastatic melanoma tumors and patient-derived cell lines. The overall structure, diversity, and taxonomy of the fecal microbiome did not differ by BMI. CONCLUSIONS: These findings suggest that the host metabolic phenotype influences melanoma metabolism and provide insight into the improved outcomes observed in OW/OB patients with metastatic melanoma treated with ICIs and targeted therapies

Novel roles of the RB-pathway in human cancers: Modifying disease progression and establishing new therapeutic opportunities

Deregulation of the retinoblastoma (RB) tumor suppressor pathway, a critical negative regulator of cell cycle control and proliferation, is observed in a wide variety of human cancers. Emerging studies have implicated RB protein function not only in cell proliferation but also in other essential cellular processes such as differentiation and chromosomal instability, among others. However, how deregulation of the RB-pathway directly impacts certain critical aspects of tumorigenesis and disease progression still remains an enigma. Herein, using breast cancer models, we have identified novel implications of RB-pathway deregulation that contribute to disease progression. RB loss in cooperation with epidermal growth factor 2 (ErbB2), a prominent oncogene activated in breast cancer, promotes structural and organizational changes in mammary epithelial cells correlating with an epithelial-to-mesenchymal transition gene signature, and ultimately an invasive phenotype in mammary lesions in vivo. Additionally, due to the clear importance of RB in suppressing tumorigenesis in multiple tissue types, we examined the efficacy of using a small molecule CDK4/6 inhibitor (PD-0332991) to activate RB function as a potential therapeutic modality in both early stage breast cancer and advanced liver cancer models. CDK4/6 inhibition was observed to be highly effective at inducing a potent cytostatic response in both model systems. Importantly, we demonstrate that the efficacy of PD-0332991 is dependent on the expression of multiple key players in cell cycle control aside from RB itself, including the other pocket proteins (p107/p130), p16 ink4a and Cyclin D1. Together these studies demonstrate the utility of RB-pathway status as both a predictor for invasive disease and a novel therapeutic target

RB and p53 cooperate to prevent liver tumorigenesis in response to tissue damage.

The tumor suppressors retinoblastoma (RB) and p53 are important regulators of the cell cycle. Although human cancer cells inactivate RB and p53 by many mechanisms, the cooperative roles of these proteins in tumorigenesis are complex and tissue specific. We analyzed the cooperation of RB and p53 in liver development and pathogenesis of hepatocellular carcinoma. Spontaneous and carcinogen-induced (diethylnitrosamine) tumorigenesis were studied in mice with liver-specific deletions of Rb and/or p53 (Rbf/f;albcre+, p53f/f;albcre+ and Rbf/f; p53f/f;albcre+ mice). Genotype, histologic, immunohistochemical, microarray, quantitative polymerase chain reaction, immunoblot, and comparative genomic hybridization analyses were performed using normal and tumor samples. Comparative microarray analyses were performed against publicly available human microarray data sets. Deletion of RB and p53 from livers of mice deregulated the transcriptional programs associated with human disease. These changes were not sufficient for spontaneous tumorigenesis; potent quiescence mechanisms compensated for loss of these tumor suppressors. In response to hepatocarcinogen-induced damage, distinct and cooperative roles of RB and p53 were revealed; their loss affected cell cycle control, checkpoint response, and genome stability. In damaged tissue, combined loss of RB and p53 resulted in early lesion formation, aggressive tumor progression, and gene expression signatures and histologic characteristics of advanced human hepatocellular carcinoma. The effects RB and p53 loss are determined by the tissue environment; cell stresses that promote aggressive disease reveal the functions of these tumor suppressors. Copyright © 2011 AGA Institute. Published by Elsevier Inc. All rights reserved

PI3K therapy reprograms mitochondrial trafficking to fuel tumor cell invasion

Molecular therapies are hallmarks of "personalized" medicine, but how tumors adapt to these agents is not well-understood. Here we show that small-molecule inhibitors of phosphatidylinositol 3-kinase (PI3K) currently in the clinic induce global transcriptional reprogramming in tumors, with activation of growth factor receptors, (re)phosphorylation of Akt and mammalian target of rapamycin (mTOR), and increased tumor cell motility and invasion. This response involves redistribution of energetically active mitochondria to the cortical cytoskeleton, where they support membrane dynamics, turnover of focal adhesion complexes, and random cell motility. Blocking oxidative phosphorylation prevents adaptive mitochondrial trafficking, impairs membrane dynamics, and suppresses tumor cell invasion. Therefore, "spatiotemporal" mitochondrial respiration adaptively induced by PI3K therapy fuels tumor cell invasion, and may provide an important antimetastatic target.ope

ClpXP regulates mitochondrial SDHB folding.

<p>(<b>A</b>) PC3 cells were transfected with control siRNA (Ctrl) or ClpP-directed siRNA and solubilized in the indicated concentrations of detergent (CHAPS), and insoluble fractions were analyzed by western blotting. The position of oxidative phosphorylation complex (C) subunits are indicated. (<b>B</b>) PC3 cells were transfected with control siRNA (Ctrl) or ClpP-directed siRNA and mixed with increasing concentrations of detergent (CHAPS), and insoluble fractions were analyzed by western blotting. Three independent experiments per condition are shown. (<b>C</b>) Densitometric quantification of protein bands in control or ClpP siRNA transfectants, as in (<b>B</b>). Data are the mean ± SEM of four (SDHB) or three (SDHA, COX-IV) independent experiments. (<b>D</b>) PC3 cells transfected with control siRNA (Ctrl) or ClpP-or ClpX-directed siRNA were mixed with the indicated increasing concentrations of CHAPS, and insoluble material was analyzed by western blotting. Raw data for this figure can be found in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002507#pbio.1002507.s001" target="_blank">S1 Data</a>.</p