Jinhai Guo

TMEM166, a novel transmembrane protein, regulates cell autophagy and apoptosis

Programmed cell death can be divided into apoptosis and autophagic cell death. We describe the biological activities of TMEM166 (transmembrane protein 166, also known as FLJ13391), which is a novel lysosome and endoplasmic reticulum-associated membrane protein containing a putative TM domain. Overexpression of TMEM166 markedly inhibited colony formation in HeLa cells. Simultaneously, typical morphological characteristics consistent with autophagy were observed by transmission electron microscopy, including extensive autophagic vacuolization and enclosure of cell organelles by double-membrane structures. Further experiments confirmed that the overexpression of TMEM166 increased the punctate distribution of MDC staining and GFP-LC3 in HeLa cells, as well as the LC3-II/LC3-I proportion. On the other hand, TMEM166-transfected HeLa and 293T cells succumbed to cell death with hallmarks of apoptosis including phosphatidylserine externalization, loss of mitochondrial transmembrane potential, caspase activation and chromatin condensation. Kinetic analysis revealed that the appearance of autophagy-related biochemical parameters preceded the nuclear changes typical of apoptosis in TMEM166-transfected HeLa cells. Suppression of TMEM166 expression by small interference RNA inhibited starvation-induced autophagy in HeLa cells. These findings show for the first time that TMEM166 is a novel regulator involved in both autophagy and apoptosis.

Protein tyrosine phosphatase interacting protein 51 (PTPIP51) is a novel mitochondria protein with an N-terminal mitochondrial targeting sequence and induces apoptosis

Apoptosis is a genetically determined cell suicide program. Mitochondria play a central role in this process and various molecules have been shown to regulate apoptosis in this organelle. In the present study, we firstly identified that protein tyrosine phosphatase interacting protein 51 (PTPIP51) is a novel mitochondrial protein, which may induce apoptosis in HEK293T and HeLa cell lines. PTPIP51 transfection resulted in the externalization of phosphatidylserine (PS), activation of caspase-3, cleavage of PARP, and condensation of nuclear DNA. Further investigation revealed that PTPIP51 over-expression caused a decrease in mitochondrial membrane potential and release of cytochrome c, suggesting that it may be involved in a mitochondria/cytochrome c mediated apoptosis pathway. We also found that a putative TM domain near the N terminus of PTPIP51 is required for its targeting to mitochondria, as evidenced by the finding that deletion of the PTPIP51 TM domain prevented the proteins mitochondiral localization. Furthermore, this deletion significantly influenced the ability of PTPIP51 to induce apoptosis. Taken together, the results of the present study suggest that PTPIP51 is a mitochondrial protein with apoptosis-inducing function and that the N-terminal TM domain is required for both the correct targeting of the protein to mitochondria and its apoptotic functions.

Cell-Based Screening and Validation of Human Novel Genes Associated with Cell Viability

In the present study, a cell-based high-throughput assay is established to identify novel human genes associated with cell viability. The assay relies on the down-regulation of Renilla luciferase (pRL) activity in a 96-well format. In addition, 2-color fluorescence probes were used to distinguish living and dead cells. As the positive control, the authors used the expression vectors encoding Bax, TNFRSF1A, and TAJ, which were widely known to effectively induce programmed cell death. They screened 409 novel genes (including alternative mRNA splicing forms) cloned in their laboratory and found that 39 genes could significantly down-regulate pRL activity. A subsequent fluorescence-based assay revealed that 4 of the 39 genes (PIP5KL1, OLFM1, RNF122, FAM26B) were associated with cell viability. Further function assays validated that the 4 genes were able to induce both necrosis and apoptosis. These results therefore indicate that a rapid and effective screening system has been developed, which should shed light on some functions of novel genes.

Adenovirus vector-mediated expression of TMEM166 inhibits human cancer cell growth by autophagy and apoptosis in vitro and in vivo

TMEM166 is a novel programmed cell death-related molecule. In this report, we constructed a recombinant adenovirus 5-TMEM166 vector (Ad5-TMEM166) and evaluated its expression and anti-tumor activities in vitro and in vivo. Cell viability analysis revealed that the adenovirus-mediated increase of TMEM166 inhibited tumor cell growth in a dose- and time-dependent manner. This inhibitory effect was mediated by both autophagy (via inhibition of mTOR and activation of p70S6K) and apoptosis (via caspase-3 activation), both of which contributed to cell death and suppression of tumorigenicity. Our data indicated that Ad5-TMEM166 may be a novel gene therapy candidate for cancer.

High-throughput cell-based screening reveals a role for ZNF131 as a repressor of ERalpha signaling

BackgroundEstrogen receptor α (ERα) is a transcription factor whose activity is affected by multiple regulatory cofactors. In an effort to identify the human genes involved in the regulation of ERα, we constructed a high-throughput, cell-based, functional screening platform by linking a response element (ERE) with a reporter gene. This allowed the cellular activity of ERα, in cells cotransfected with the candidate gene, to be quantified in the presence or absence of its cognate ligand E2.ResultsFrom a library of 570 human cDNA clones, we identified zinc finger protein 131 (ZNF131) as a repressor of ERα mediated transactivation. ZNF131 is a typical member of the BTB/POZ family of transcription factors, and shows both ubiquitous expression and a high degree of sequence conservation. The luciferase reporter gene assay revealed that ZNF131 inhibits ligand-dependent transactivation by ERα in a dose-dependent manner. Electrophoretic mobility shift assay clearly demonstrated that the interaction between ZNF131 and ERα interrupts or prevents ERα binding to the estrogen response element (ERE). In addition, ZNF131 was able to suppress the expression of pS2, an ERα target gene.ConclusionWe suggest that the functional screening platform we constructed can be applied for high-throughput genomic screening candidate ERα-related genes. This in turn may provide new insights into the underlying molecular mechanisms of ERα regulation in mammalian cells.

Human HS1BP3 induces cell apoptosis and activates AP-1.

In the present study, we characterized the function of HS1-binding protein 3 (HS1BP3), which is mutated in essential tremor and may be involved in lymphocyte activation. We found that HS1BP3 localized to the mitochondria and endoplasmic reticulum partially. Overexpression of HS1BP3 induced apoptosis in HEK293T and HeLa cell lines. When these cell lines were transfected with HS1BP3, they exhibited nuclear DNA condensation, externalization of phosphatidylserine (PS), and cleavage of poly ADP ribose polymerase (PARP). Furthermore, suppression of HS1BP3 or HS1 expression attenuates HS1BP3 induced apoptosis. In addition, HS1BP3 enhanced activator protein 1 (AP-1)-mediated transcription in a dose-dependent manner. Therefore, we conclude that HS1BP3 regulates apoptosis via HS1 and stimulates AP-1-mediated transcription.