Jingxue Shi

CHCM1/CHCHD6, Novel Mitochondrial Protein Linked to Regulation of Mitofilin and Mitochondrial Cristae Morphology

Background: Functional characterization of a novel mitochondrial protein, CHCM1/CHCHD6, is reported. Results: CHCM1 interacts with Mitofilin, DISC1, and CHCHD3, and its deficiency leads to severe defects in mitochondrial cristae morphology, reduction in cell growth, ATP production, and oxygen consumption. Conclusion: CHCM1/CHCHD6 is a novel player linked to mitochondrial cristae morphology. Significance: Results provide valuable insights into molecular events controlling the structural integrity and biogenesis of mitochondrial cristae. The structural integrity of mitochondrial cristae is crucial for mitochondrial functions; however, the molecular events controlling the structural integrity and biogenesis of mitochondrial cristae remain to be fully elucidated. Here, we report the functional characterization of a novel mitochondrial protein named CHCM1 (coiled coil helix cristae morphology 1)/CHCHD6. CHCM1/CHCHD6 harbors a coiled coil helix-coiled coil helix domain at its C-terminal end and predominantly localizes to mitochondrial inner membrane. CHCM1/CHCHD6 knockdown causes severe defects in mitochondrial cristae morphology. The mitochondrial cristae in CHCM1/CHCHD6-deficient cells become hollow with loss of structural definitions and reduction in electron-dense matrix. CHCM1/CHCHD6 depletion also leads to reductions in cell growth, ATP production, and oxygen consumption. CHCM1/CHCHD6 through its C-terminal end strongly and directly interacts with the mitochondrial inner membrane protein mitofilin, which is known to also control mitochondrial cristae morphology. CHCM1/CHCHD6 also interacts with other mitofilin-associated proteins, including DISC1 and CHCHD3. Knockdown of CHCM1/CHCHD6 reduces mitofilin protein levels; conversely, mitofilin knockdown leads to reduction in CHCM1 levels, suggesting coordinate regulation between these proteins. Our results further indicate that genotoxic anticancer drugs that induce DNA damage down-regulate CHCM1/CHCHD6 expression in multiple human cancer cells, whereas mitochondrial respiratory chain inhibitors do not affect CHCM1/CHCHD6 levels. CHCM1/CHCHD6 knockdown in human cancer cells enhances chemosensitivity to genotoxic anticancer drugs, whereas its overexpression increases resistance. Collectively, our results indicate that CHCM1/CHCHD6 is linked to regulation of mitochondrial cristae morphology, cell growth, ATP production, and oxygen consumption and highlight its potential as a possible target for cancer therapeutics.

Dihydroartemisinin upregulates death receptor 5 expression and cooperates with TRAIL to induce apoptosis in human prostate cancer cells.

Dihydroartemisinin (DHA) is a derivative of artemisinin and is an effective anti-malaria therapeutic used worldwide. In this report, we report that DHA is as a potential anti-cancer drug for prostate cancer. Our data indicate that DHA suppresses the PI3-K/Akt and ERK cell survival pathways and triggers the induction of death receptor DR5 and activation of extrinsic and intrinsic cell death signaling. DHA-mediated DR5 induction appears to occur via increased transcriptional activity of DR5 promoter. Our data also show that, while DHA has strong cytotocixity in tumor cells, it exhibits minimal cytotoxic effects on normal prostate epithelial cells. Our studies also demonstrate that DHA worked cooperatively with death ligand TRAIL. Combination of DHA and TRAIL significantly enhanced cell killing above that noted with a single agent alone. Based on these results, we propose a novel idea of developing DHA alone and/or in combination with TRAIL for the treatment of prostate cancer.

PDRG1, a novel tumor marker for multiple malignancies that is selectively regulated by genotoxic stress

We have previously cloned and characterized a novel p53 and DNA damage-regulated gene named PDRG1. PDRG1 was found to be differentially regulated by ultraviolet (UV) radiation and p53. In this study, we further investigated stress regulation of PDRG1 and found it to be selectively regulated by agents that induce genotoxic stress (DNA damage). Using cancer profiling arrays, we also investigated PDRG1 expression in matching normal and tumor samples representing various malignancies and found its expression to be upregulated in multiple malignancies including cancers of the colon, rectum, ovary, lung, stomach, breast and uterus when compared to their respective matched normal tissues. Western blot and immunohistochemical analyses were also performed on select specimen sets of colon cancers and matching normal tissues and the results also indicated PDRG1 overexpression in tumors relative to normal tissues. To gain insight into the function of PDRG1, we performed PDRG1 knockdown in human colon cancer cells and found its depletion to result in marked slowdown of tumor cell growth. These results suggest that PDGR1 may be linked to cell growth regulation. Yeast two-hybrid screen also led to the identification of PDCD7, CIZ1 and MAP1S as PDRG1-interacting proteins that are involved in apoptosis and cell cycle regulation which further implicate PDRG1 in controlling cell growth regulation. Taken together, our results indicate that PDRG1 expression is increased in multiple human malignancies suggesting it to be a high-value novel tumor marker that could play a role in cancer development and/or progression.

Potential Tumor Suppressive Role of Monoglyceride Lipase in Human Colorectal Cancer

Human monoglyceride lipase (MGL) is a recently identified lipase and very little is known about its regulation and function in cellular regulatory processes, particularly in context to human malignancy. In this study, we investigated the regulation and function of MGL in human cancer(s) and report that MGL expression was either absent or reduced in the majority of primary colorectal cancers. Immunohistochemical studies showed that reduction of MGL expression in the colorectal tumor tissues predominantly occurred in the cancerous epithelial cells. MGL was found to reside in the core surface of a cellular organelle named ‘lipid body’. Furthermore, it was found to interact selectively with a number of phospholipids, including phosphatidic acid and phosphoinositol(3,4,5)P3, phosphoinositol(3,5)P2, phosphoinositol(3,4)P2 and several other phosphoinositides, and among all phosphoinositides analyzed, its interaction with PI(3,4,5)P3 was found to be the strongest. In addition, overexpression of MGL suppressed colony formation in tumor cell lines and knockdown of MGL resulted in increased Akt phosphorylation. Taken together, our results suggest that MGL plays a negative regulatory role in phosphatidylinositol-3 kinase/Akt signaling and tumor cell growth.

DOC45, a Novel DNA Damage–Regulated Nucleocytoplasmic ATPase That Is Overexpressed in Multiple Human Malignancies

In this article, we report the characterization of a novel DNA damage–regulated gene, named DNA damage–regulated overexpressed in cancer 45 (DOC45). Our results indicate that DNA damage–inducing agents, including doxorubicin (adriamycin), etoposide, and ionizing and UV radiation, strongly downregulate DOC45 expression, whereas endoplasmic reticulum stress–inducing agents do not. Our results also indicate that DOC45 is overexpressed in several human malignancies, including cancers of the colon, rectum, ovary, lung, stomach, and uterus. DOC45 harbors conserved nucleotide triphosphate–binding motifs and is capable of ATP hydrolysis, findings that highlight its function as a novel ATPase. Although predominantly cytoplasmic, DOC45 exhibits a characteristic nucleocytoplasmic distribution and, on inhibition of nuclear export, predominantly accumulates in the nucleoli. These results suggest that DOC45 may shuttle between nucleus and cytoplasm to carry out its function. Our results also indicate that DOC45 expression is enhanced during oncogenic Ras-mediated transformation and that its expression is linked to phosphoinositide 3-kinase signaling pathway. Furthermore, short hairpin RNA–mediated knockdown of DOC45 in human colon cancer cells inhibits their proliferation and enhances cellular sensitivity to doxorubicin-induced cell death, suggesting that DOC45 plays an important role in cell proliferation and survival. Collectively, our results indicate that DOC45 is a novel ATPase that is linked to cellular stress response and tumorigenesis, and may also serve as a valuable tumor marker. Mol Cancer Res; 8(1); 57–66

Negative regulation of p53 by Ras superfamily protein RBEL1A

Summary We had previously reported that RBEL1A, a novel Ras-like GTPase, was overexpressed in multiple human malignancies and that its depletion suppressed cell growth. However, the underlying molecular mechanism remained to be elucidated. Here we report that depletion of endogenous RBEL1A results in p53 accumulation due to increased p53 half-life whereas increased expression of RBEL1A reduces p53 levels under unstressed and genotoxic stress conditions. RBEL1A directly interacts with p53 and MDM2, and strongly enhances MDM2-dependent p53 ubiquitylation and degradation. We also found that RBEL1A modulation of p53 ubiquitylation by MDM2 does not depend on its GTPase activity. We have also defined the p53 oligomeric domain and RBEL1A GTPase domain to be the crucial regions for p53–RBEL1A interactions. Importantly, we have found that RBEL1A strongly interferes with p53 transactivation function; thus our results indicate that RBEL1A appears to function as a novel p53 negative regulator that facilitates MDM2-dependent p53 ubiquitylation and degradation.

The promise of paclitaxel-peptide conjugates for MMP-2-targeted drug delivery

Commentary to: Biological evaluation of Paclitaxel-peptide conjugates as a model for MMP2-targeted drug delivery Roppei Yamada, Maya B. Kostova, Ravi Kumar Anchoori, Shili Xu, Nouri Neamati and Saeed R. Khan

Abstract 3841: RBEL1A, a novel GTPase is an important regulator of cell growth and cell survival

We have recently reported the characterization of RBEL1 proteins, a novel subfamily of the Ras/Rab-like GTPases. Our studies demonstrate that RBEL1 proteins have Ras-like GTPase activity and differentially regulate the ERK signaling pathway. Our studies also demonstrate that RBEL1A is overexpressed in the majority of breast cancers and a large segment of colon cancers. Knockdown of RBEL1A negatively affects cell growth and induces apoptosis, suggesting that RBEL1A is critical for regulation of cell growth and survival. To investigate the molecular mechanisms by which RBEL1A mediates its function, we have studied a number of RBEL1A-interacting proteins. Our results indicate that RBEL1A interacts with p53 and negatively regulates p53 function via a proteasome-dependent pathway. We have also examined the molecular interactions between RBEL1A and p53 and our results demonstrate that RBEL1A is an important negative regulator of p53 that affects p53-mediated functions. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3841. doi:10.1158/1538-7445.AM2011-3841