Adaptation of transgene mRNA translation boosts the anticancer efficacy of oncolytic HSV1.

BACKGROUND: Transgenes deliver therapeutic payloads to improve oncolytic virus immunotherapy. Transgenes encoded within oncolytic viruses are designed to be highly transcribed, but protein synthesis is often negatively affected by viral infection, compromising the amount of therapeutic protein expressed. Studying the oncolytic herpes simplex virus-1 (HSV1), we found standard transgene mRNAs to be suboptimally translated in infected cells. METHODS: Using RNA-Seq reads, we determined the transcription start sites and 5'leaders of HSV1 genes and uncovered the US11 5'leader to confer superior activity in translation reporter assays. We then incorporated this 5'leader into GM-CSF expression cassette in oncolytic HSV1 and compared the translationally adapted oncolytic virus with the conventional, leaderless, virus in vitro and in mice. RESULTS: Inclusion of the US11 5'leader in the GM-CSF transgene incorporated into HSV1 boosted translation in vitro and in vivo. Importantly, treatment with US11 5'leader-GM-CSF oncolytic HSV1 showed superior antitumor immune activity and improved survival in a syngeneic mouse model of colorectal cancer as compared with leaderless-GM-CSF HSV1. CONCLUSIONS: Our study demonstrates the therapeutic value of identifying and integrating platform-specific cis-acting sequences that confer increased protein synthesis on transgene expression.

mTORC1 promotes TOP mRNA translation through site-specific phosphorylation of LARP1.

LARP1 is a key repressor of TOP mRNA translation. It binds the m7Gppp cap moiety and the adjacent 5'TOP motif of TOP mRNAs, thus impeding the assembly of the eIF4F complex on these transcripts. mTORC1 controls TOP mRNA translation via LARP1, but the details of the mechanism are unclear. Herein we elucidate the mechanism by which mTORC1 controls LARP1's translation repression activity. We demonstrate that mTORC1 phosphorylates LARP1 in vitro and in vivo, activities that are efficiently inhibited by rapamycin and torin1. We uncover 26 rapamycin-sensitive phospho-serine and -threonine residues on LARP1 that are distributed in 7 clusters. Our data show that phosphorylation of a cluster of residues located proximally to the m7Gppp cap-binding DM15 region is particularly sensitive to rapamycin and regulates both the RNA-binding and the translation inhibitory activities of LARP1. Our results unravel a new model of translation control in which the La module (LaMod) and DM15 region of LARP1, both of which can directly interact with TOP mRNA, are differentially regulated: the LaMod remains constitutively bound to PABP (irrespective of the activation status of mTORC1), while the C-terminal DM15 'pendular hook' engages the TOP mRNA 5'-end to repress translation, but only in conditions of mTORC1 inhibition.

Interactions between breast cancer cells and bone marrow derived cells in vitro define a role for osteopontin in affecting breast cancer cell migration.

The preferential metastasis of breast cancer cells to bone is a complex set of events including homing and preferential growth which may include unique factors produced by bone cells in the immediate microenvironment. In this study, we evaluated the suitability of bone cells derived from orthoplastic surgeries for use in an in vitro co-culture system representing a model of the bone microenvironment. Using a limiting dilution assay we determined the relative survival and proliferation potentials of breast cancer cell lines co-cultured on bone-derived cells or on Hs68 fibroblasts. The comparison of bone and skin fibroblastic substrata indicates that MCF-7 cells preferentially survive and grow in a bone microenvironment (P < 0.001). Overall, we show that bone-derived cells enhance survival, proliferation, and migration of breast cancer cells, where migration is in part mediated by bone cell-produced osteopontin. Our in vitro co-culture model system provides a robust cost-effective method to study the various factors that mediate cancer/bone-derived cell interactions.

Reovirus oncolysis: the Ras/RalGEF/p38 pathway dictates host cell permissiveness to reovirus infection.

Reovirus is a benign human virus that was recently found to have oncolytic properties and is currently in clinical trials as a potential cancer therapy. We have previously demonstrated that activation of Ras signaling, a common event in cancer, renders cells susceptible to reovirus oncolysis. In this study, we investigate which elements downstream of Ras are important in reovirus infection. By using a panel of NIH 3T3 cells transformed with activated Ras mutated in the effector-binding domain, we found that only the RasV12G37 mutant, which was unable to signal to Raf or phosphatidylinositol 3-kinase but retained signaling capability to guanine nucleotide-exchange factors (GEFs) for the small G protein, Ral (known as RalGEFs), was permissive to reovirus. Expression of the activated mutant of the RalGEF, Rlf, also allowed reovirus replication. Specific inhibition of the Ral pathway by using dominant-negative RalA rendered normally permissive H-Ras cells (cells expressing activated Ras) resistant to reovirus. To further identify elements downstream of RalGEF that promote reovirus infection, we used chemical inhibitors of the downstream signaling elements p38 and JNK. We found that reovirus infection was blocked in the presence of the p38 inhibitor but not the JNK inhibitor. Together, these results implicate a Ras/RalGEF/p38 pathway in the regulation of reovirus replication and oncolysis.