The mediators of the DNA damage response (DDR) are highly phosphorylated by kinases that control cell proliferation, but little is known about the role of this regulation. Here we show that cell cycle phosphorylation of the prototypical DDR mediator Saccharomyces cerevisiae Rad9 depends on cyclin-dependent kinase (CDK) complexes. We find that a specific G2/M form of Cdc28 can phosphorylate in vitro the N-terminal region of Rad9 on nine consensus CDK phosphorylation sites. We show that the integrity of CDK consensus sites and the activity of Cdc28 are required for both the activation of the Chk1 checkpoint kinase and its interaction with Rad9. We have identified T125 and T143 as important residues in Rad9 for this Rad9/Chk1 interaction. Phosphorylation of T143 is the most important feature promoting Rad9/Chk1 interaction, while the much more abundant phosphorylation of the neighbouring T125 residue impedes the Rad9/Chk1 interaction. We suggest a novel model for Chk1 activation where Cdc28 regulates the constitutive interaction of Rad9 and Chk1. The Rad9/Chk1 complex is then recruited at sites of DNA damage where activation of Chk1 requires additional DDR–specific protein kinases.

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Glioblastoma Multiforme (GBM) is the most aggressive form of adult brain tumor with a median survival time of twelve months. GBM is highly resistant to conventional therapy which includes surgical resection of the tumor, radiation treatment and chemotherapy. GBM cells are highly motile and invasive resulting in infiltrative tumors with poorly defined borders. GBM tumors are heavily infiltrated with microglia cells which are known to stimulate GBM cell invasion. Our laboratory has previously demonstrated that microglia strongly stimulates GBM invasion both in-vitro and in orthotopic animal models. This interaction was found to be dependent on CSF-1R which is expressed on all tumor infiltrating macrophages/microglia. Blockade of the CSF-1R using compounds such as pexidartinib (PLX3397) can inhibit microglia/macrophage-stimulated GBM invasion in-vitro and in vivo. A variety of chemokines are upregulated in the GBM tumor microenvironment and facilitate “cross-talk” between microglia and GBM cells eliciting a chemotactic response. We have demonstrated that the chemotactic ligand, CCL3, is similarly upregulated in GBM tumors. We postulated that inhibition of CCL3 associated receptors such as C-C receptor 1 (CCR1) might also inhibit GBM invasion, thus, a CCR1 antagonist could prove efficacious for blockade of microglia-induced glioblastoma invasion in vitro. Many potent CCR1 antagonists have been described in the literature. We chose four of these compounds with two distinct structural cores, all with reported IC50’s of less than 200 nM for inhibition of CCR1 binding versus CCL3. We examined the ability of these antagonists to block microglia-stimulated glioblastoma invasion using an in-vitro coculture invasion assay. Using quantitative PCR arrays, we also show that expression of chemokines and chemokine receptor genes is greatly altered in GBM conditioned media-treated microglia. Understanding the pattern of tumor-associated macrophage/microglia chemokine secretion in GBM may present additional targets for chemotherapeutic intervention and enhance immunotherapy. Citation Format: Salvatore J. Coniglio, Poornema Ramasundaram, Neshama Fournier, Danielle S. Hamilton, Gregory Marshall, Keia Smith, Diana Habib, James R. Merritt. The chemokine receptor CCR1 is involved in microglia stimulated glioblastoma invasion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4548.