A genetic screen for modifiers of Drosophila caspase Dcp-1 reveals caspase involvement in autophagy and novel caspase-related genes.

BACKGROUND: Caspases are cysteine proteases with essential functions in the apoptotic pathway; their proteolytic activity toward various substrates is associated with the morphological changes of cells. Recent reports have described non-apoptotic functions of caspases, including autophagy. In this report, we searched for novel modifiers of the phenotype of Dcp-1 gain-of-function (GF) animals by screening promoter element- inserted Drosophila melanogaster lines (EP lines). RESULTS: We screened approximately 15,000 EP lines and identified 72 Dcp-1-interacting genes that were classified into 10 groups based on their functions and pathways: 4 apoptosis signaling genes, 10 autophagy genes, 5 insulin/IGF and TOR signaling pathway genes, 6 MAP kinase and JNK signaling pathway genes, 4 ecdysone signaling genes, 6 ubiquitination genes, 11 various developmental signaling genes, 12 transcription factors, 3 translation factors, and 11 other unclassified genes including 5 functionally undefined genes. Among them, insulin/IGF and TOR signaling pathway, MAP kinase and JNK signaling pathway, and ecdysone signaling are known to be involved in autophagy. Together with the identification of autophagy genes, the results of our screen suggest that autophagy counteracts Dcp-1-induced apoptosis. Consistent with this idea, we show that expression of eGFP-Atg5 rescued the eye phenotype caused by Dcp-1 GF. Paradoxically, we found that over-expression of full-length Dcp-1 induced autophagy, as Atg8b-GFP, an indicator of autophagy, was increased in the eye imaginal discs and in the S2 cell line. Taken together, these data suggest that autophagy suppresses Dcp-1-mediated apoptotic cell death, whereas Dcp-1 positively regulates autophagy, possibly through feedback regulation. CONCLUSIONS: We identified a number of Dcp-1 modifiers that genetically interact with Dcp-1-induced cell death. Our results showing that Dcp-1 and autophagy-related genes influence each other will aid future investigations of the complicated relationships between apoptosis and autophagy.

Altered expression of phosphatase of regenerating liver gene family in non-small cell lung cancer.

Protein tyrosine phophatases (PTPs) are implicated in the tumorigenesis and metastasis of human cancer. The phosphatase of regenerating liver (PRL) gene family, a subgroup of PTPs is also linked to these processes. In many solid cancers, high levels of PRL-3 expression are related with metastasis and poor prognosis. However, the expression patterns of PRL-1 and -2 have not been explored in lung cancer yet. Thus, we investigated the expression levels of PRL-1, -2 and -3 in the tissues of primary lung cancer patients. The protein expression levels of PRL-2, but not PRL-1 and -3 were increased in cancer tissues. However, there was no correlation between mRNA and protein expression levels of the PRLs. Reporter assays showed that PRLs suppressed the activity of the p21 promoter but promoted AP-1 activity. Furthermore, transfection of PRLs showed significantly increased cell proliferation. Therefore, these results suggest that PRL-2 plays an important role in lung cancer and can be a biomarker of lung cancer, substituting for the function of other PRLs.

Downregulation of p53 by phosphatase of regenerating liver 3 is mediated by MDM2 and PIRH2.

AIMS: The phosphatase of regenerating liver (PRL) family is related to tumorigenesis and metastasis in various cancer types. Its overexpression increases cell motility and proliferation via the downregulation of p21 expression. In a previous study, we reported that PRL-1 downregulates p53 and is a target gene of p53. In this study, we investigated whether a member of the PRL family, PRL-3, could regulate p53 like PRL-1 in cancer cells. MAIN METHODS: To elucidate the role of PRL-3 in regulating p53 in cancer cells, we used a cell culture system to measure protein level, transcriptional level, apoptosis or localization. KEY FINDINGS: We determined that PRL-3 overexpression reduced the activity of the p21 and p53 reporters. Additionally, the levels of endogenous and exogenous p53 protein were reduced in cells transiently expressing PRL-3, whereas the ablation of PRL-3 by siRNA increased levels of the p53 protein. The downregulation of p53 by PRL-3 inhibited p53-mediated apoptosis. However, the phosphatase-dead mutant C104S, prenylated-site mutant C170S, and C104S/C170S PRL-3 evidenced minimal effects on the downregulation of p53 protein as compared with wild-type PRL-3. Further examinations revealed that PRL-3 expression reduced the stability of p53 by inducing the transcription of p53 induced protein with a RING-H2 domain (PIRH2) through early growth response (EGR) and by increasing the phosphorylation of mouse double minute 2 (MDM2), and then both negatively regulated p53. SIGNIFICANCE: These findings demonstrated that PRL-3, like PRL-1, can negatively regulate p53 via the activation of PIRH2 and MDM2 in cancer cells.