Tumor progression is independent of tumor-associated macrophages in cell lineage-based mouse models of glioblastoma.

Macrophage targeting therapies have had limited clinical success in glioblastoma (GBM). Further understanding the GBM immune microenvironment is critical for refining immunotherapeutic approaches. Here, we use genetically engineered mouse models and orthotopic transplantation-based GBM models with identical driver mutations and unique cells of origin to examine the role of tumor cell lineage in shaping the immune microenvironment and response to tumor-associated macrophage (TAM) depletion therapy. We show that oligodendrocyte progenitor cell lineage-associated GBMs (Type 2) recruit more immune infiltrates and specifically monocyte-derived macrophages than subventricular zone neural stem cell-associated GBMs (Type 1). We then devise a TAM depletion system that offers a uniquely robust and sustained TAM depletion. We find that extensive TAM depletion in these cell lineage-based GBM models affords no survival benefit. Despite the lack of survival benefit of TAM depletion, we show that Type 1 and Type 2 GBMs have unique molecular responses to TAM depletion. In sum, we demonstrate that GBM cell lineage influences TAM ontogeny and abundance and molecular response to TAM depletion.

Stem-like cells drive NF1-associated MPNST functional heterogeneity and tumor progression.

NF1-associated malignant peripheral nerve sheath tumors (MPNSTs) are the major cause of mortality in neurofibromatosis. MPNSTs arise from benign peripheral nerve plexiform neurofibromas that originate in the embryonic neural crest cell lineage. Using reporter transgenes that label early neural crest lineage cells in multiple NF1 MPNST mouse models, we discover and characterize a rare MPNST cell population with stem-cell-like properties, including quiescence, that is essential for tumor initiation and relapse. Following isolation of these cells, we derive a cancer-stem-cell-specific gene expression signature that includes consensus embryonic neural crest genes and identify Nestin as a marker for the MPNST cell of origin. Combined targeting of cancer stem cells along with antimitotic chemotherapy yields effective tumor inhibition and prolongs survival. Enrichment of the cancer stem cell signature in cognate human tumors supports the generality and relevance of cancer stem cells to MPNST therapy development.

Regulation of the error-prone DNA polymerase Polκ by oncogenic signaling and its contribution to drug resistance.

The DNA polymerase Polκ plays a key role in translesion synthesis, an error-prone replication mechanism. Polκ is overexpressed in various tumor types. Here, we found that melanoma and lung and breast cancer cells experiencing stress from oncogene inhibition up-regulated the expression of Polκ and shifted its localization from the cytoplasm to the nucleus. This effect was phenocopied by inhibition of the kinase mTOR, by induction of ER stress, or by glucose deprivation. In unstressed cells, Polκ is continually transported out of the nucleus by exportin-1. Inhibiting exportin-1 or overexpressing Polκ increased the abundance of nuclear-localized Polκ, particularly in response to the BRAFV600E-targeted inhibitor vemurafenib, which decreased the cytotoxicity of the drug in BRAFV600E melanoma cells. These observations were analogous to how Escherichia coli encountering cell stress and nutrient deprivation can up-regulate and activate DinB/pol IV, the bacterial ortholog of Polκ, to induce mutagenesis that enables stress tolerance or escape. However, we found that the increased expression of Polκ was not excessively mutagenic, indicating that noncatalytic or other functions of Polκ could mediate its role in stress responses in mammalian cells. Repressing the expression or nuclear localization of Polκ might prevent drug resistance in some cancer cells.