Cyclooxygenase-2 (COX-2) is linked to worse prognosis in patients with malignant gliomas and other tumor types. Amplification/overexpression of epidermal growth factor receptor (EGFR) is commonly seen in these tumors. We have previously shown that EGFR signaling, through activation of p38-mitogen activated protein kinase (MAPK), protein kinase C-δ (PKC-δ), and Sp1, plays an important role in the regulation of COX-2 expression in glioma cells. Here, we report that the Src kinase also has a role in this signaling cascade upstream of p38-MAPK/PKC-δ. In addition, more detailed analysis revealed the involvement of FOXM1, a member of the forkhead box family of transcriptional activators, in EGF-dependent COX-2 induction. FOXM1 protein levels increase after stimulation with EGF although its role in modulating COX-2 expression does not depend on this increase. While a conventional FOXM1 responsive element resides in a distal region (−2872/−2539 relative to the transcriptional start site) of the COX-2 promoter, this is not required for EGF-dependent induction of COX-2. Instead, FOXM1 is capable of interacting with Sp1 at the Sp1 binding site (−245/−240 relative to the start site) of the COX-2 promoter and appears to act in cooperation with Sp1 to mediate EGF-induced COX-2 expression. Definition of this novel interaction provides us with a clearer understanding of the mechanistic basis for the induction of COX-2 with EGF and guides our evaluation of potential newer therapeutic targets that have relevance in this disease.

Id1 is a helix-loop-helix transcriptional modulator that increases the aggressiveness of malignant glial neoplasms. Since most glioblastomas (GBMs) show increased phosphatidylinositol-3 kinase (PI-3K) signaling, we sought to determine whether this pathway regulates Id1 expression. Higher basal Id1 expression correlates with dysregulated PI-3K signaling in multiple established GBM cell lines. Further characterization of PI-3K-dependent Id1 regulation reveals that chemical or genetic inhibition of PI-3K signaling reduces Id1 protein but not mRNA expression. Overall, PI-3K signaling appears to enhance Id1 translation with no significant effect on its stability. PI-3K signaling is known to regulate protein translation through mTORC1-dependent phosphorylation of 4E-BP1, which reduces its association with and inhibition of the translation initiation factor eIF4E. Interestingly, while inhibition of PI-3K and AKT lowers 4E-BP1 phosphorylation and expression of Id1 in all cases, inhibition of TORC1 with rapamycin does not consistently have a similar effect, suggesting an alternative mechanism for PI-3K-dependent regulation of Id1 translation. We now identify a potential role for the serine–threonine phosphatase PPM1G in translational regulation of Id1 protein expression. PPM1G knockdown by siRNA increase both 4E-BP1 phosphorylation and Id1 expression and PPM1G and 4E-BP1 co-associates in GBM cells. Furthermore, PPM1G is a phosphoprotein and this phosphorylation appears to be regulated by PI-3K activity. Finally, PI-3K inhibition increases PPM1G activity when assessed by an in vitro phosphatase assay. Our findings provide the first evidence that the PI-3K/AKT signaling pathway modulates PPM1G activity resulting in a shift in the balance between hyper- and hypo-phosphorylated 4E-BP1 and translational regulation of Id1 expression.Oncogene advance online publication, 11 April 2016; doi:10.1038/onc.2016.115.

Background A devastating late injury caused by radiation is pulmonary fibrosis. This risk may limit the volume of irradiation and compromise potentially curative therapy. Therefore, development of a therapy to prevent this toxicity can be of great benefit for this patient population. Activation of the chemokine receptor CXCR4 by its ligand stromal cell-derived factor 1 (SDF-1/CXCL12) may be important in the development of radiation-induced pulmonary fibrosis. Here, we tested whether MSX-122, a novel small molecule and partial CXCR4 antagonist, can block development of this fibrotic process. Methodology/Principal Findings The radiation-induced lung fibrosis model used was C57BL/6 mice irradiated to the entire thorax or right hemithorax to 20 Gy. Our parabiotic model involved joining a transgenic C57BL/6 mouse expressing GFP with a wild-type mouse that was subsequently irradiated to assess for migration of GFP+ bone marrow-derived progenitor cells to the irradiated lung. CXCL12 levels in the bronchoalveolar lavage fluid (BALF) and serum after irradiation were determined by ELISA. CXCR4 and CXCL12 mRNA in the irradiated lung was determined by RNase protection assay. Irradiated mice were treated daily with AMD3100, an established CXCR4 antagonist; MSX-122; and their corresponding vehicles to determine impact of drug treatment on fibrosis development. Fibrosis was assessed by serial CTs and histology. After irradiation, CXCL12 levels increased in BALF and serum with a corresponding rise in CXCR4 mRNA within irradiated lungs consistent with recruitment of a CXCR4+ cell population. Using our parabiotic model, we demonstrated recruitment of CXCR4+ bone marrow-derived mesenchymal stem cells, identified based on marker expression, to irradiated lungs. Finally, irradiated mice that received MSX-122 had significant reductions in development of pulmonary fibrosis while AMD3100 did not significantly suppress this fibrotic process. Conclusions/Significance CXCR4 inhibition by drugs such as MSX-122 may alleviate potential radiation-induced lung injury, presenting future therapeutic opportunities for patients requiring chest irradiation.

Increased COX-2 expression directly correlates with glioma grade and is associated with shorter survival in glioblastoma (GBM) patients. COX-2 is also regulated by epidermal growth factor receptor signaling which is important in the pathogenesis of GBMs. However, COX-2 expression has not been previously shown to directly alter malignancy of GBMs. Id1 is a member of the helix-loop-helix (HLH) family of transcriptional repressors that act as dominant-negative inhibitors of basic-HLH factors. This factor has been shown to be regulated by COX-2 in breast carcinoma cells and recent studies suggest that Id1 may also be involved in the genesis/progression of gliomas. We now show that COX-2 increases the aggressiveness of GBM cells. GBM cells with COX-2 overexpression show increased growth of colonies in soft agar. Tumorigenesis in vivo is also increased in both subcutaneous flank and orthotopic intracranial tumor models. COX-2 overexpression induces Id1 expression in two GBM cell lines suggesting a role for Id1 in glioma transformation/tumorigenesis. Furthermore, we find direct evidence of a role for Id1 with significant suppression of in vitro transformation and in vivo tumorigenesis in COX-2-overexpressing GBM cells where Id1 has been knocked down. In fact, Id1 is even more efficient at enhancing transformation/tumorigenesis of GBM cells than COX-2. Finally, GBM cells with COX-2 or Id1 overexpression show greater migration/invasive potential and tumors that arise from these cells also display increased microvessel density, results in line with the increased malignant potential seen in these cells. Thus, COX-2 enhances the malignancy of GBM cells through induction of Id1.

GPRC5A functions as a lung tumour suppressor to prevent spontaneous and environmentally induced lung carcinogenesis; however, the underlying mechanism remains unclear. Here we reveal that GPRC5A at the endoplasmic reticulum (ER) membrane suppresses synthesis of the secreted or membrane-bound proteins including a number of oncogenes, the most important one being Egfr. The ER-located GPRC5A disturbs the assembly of the eIF4F-mediated translation initiation complex on the mRNA cap through directly binding to the eIF4F complex with its two middle extracellular loops. Particularly, suppression of EGFR by GPRC5A contributes significantly to preventing ionizing radiation (IR)-induced lung tumorigenesis. Thus, GPRC5A deletion enhances IR-promoted EGFR expression through an increased translation rate, thereby significantly increasing lung tumour incidence in Gprc5a(-/-) mice. Our findings indicate that under-expressed GPRC5A during lung tumorigenesis enhances any transcriptional stimulation through an active translational status, which can be used to control oncogene expression and potentially the resulting related disease.