SummaryStimulation of epidermal growth factor receptor (EGFR) initiates RAS signaling simultaneously with EGFR internalization. Endocytosed EGFR is then either recycled or degraded. EGFR fate is determined in part by the RAS effector RIN1, a guanine nucleotide exchange factor (GEF) for RAB5 GTPases. EGFR degradation was slowed by RIN1 silencing, enhanced by RIN1 overexpression and accelerated by RIN1 localization to the plasma membrane. RIN1 also directly activates ABL tyrosine kinases, which regulate actin remodeling, a function not previously connected to endocytosis. We report that RIN1-RAB5 signaling favors EGFR downregulation over EGFR recycling, whereas RIN1-ABL signaling stabilizes EGFR and inhibits macropinocytosis. RIN1QM , a mutant that blocks ABL activation, caused EGF-stimulated membrane ruffling, actin remodeling, dextran uptake and EGFR degradation. An ABL kinase inhibitor phenocopied these effects in cells overexpressing RIN1. EGFR activation also promotes RIN1 interaction with BIN1, a membrane bending protein. These findings suggest that RIN1 orchestrates RAB5 activation, ABL kinase activation and BIN1 recruitment to determine EGFR fate.

Stimulation of the receptor tyrosine kinase KIT by Stem Cell Factor (SCF) triggers activation of RAS and its downstream effectors. Proper KIT activation is essential for the maturation, survival and proliferation of mast cells. In addition, SCF activation of KIT is critical for recruiting mast cells to sites of infection or injury, where they release a mix of pro-inflammatory substances. RIN3, a RAS effector and RAB5-directed guanine nucleotide exchange factor (GEF), is highly expressed and enriched in human mast cells. SCF treatment of mast cells increased the amount of GTP-bound RAB5, and the degree of RAB5 activation correlated with the expression level of RIN3. At the same time, SCF caused the dissociation of a pre-formed complex of RIN3 with BIN2, a membrane bending protein implicated in endocytosis. Silencing of RIN3 increased the rate of SCF-induced KIT internalization, while persistent RIN3 over-expression led to KIT down regulation. These observations strongly support a role for RIN3 in coordinating the early steps of KIT endocytosis. Importantly, RIN3 also functioned as an inhibitor of mast cell migration toward SCF. Finally, we demonstrate that elevated RIN3 levels sensitize mastocytosis cells to treatment with a KIT tyrosine kinase inhibitor, suggesting the value of a two-pronged inhibitor approach for this difficult to treat malignancy. These findings directly connect KIT activation with a mast cell-specific RAS effector that regulates the cellular response to SCF and provide new insight for the development of more effective mastocytosis treatments.

Pancreatic cancer is an aggressive malignancy with a 5 year survival rate of less than five percent. The predominant immune cells infiltrating the tumor microenvironment are monocytes/macrophages, which are reported to support tumor growth by suppressing host immune responses to the tumor. Recruitment of monocytes to various tissues, including tumors, is dependent upon activation of the chemokine receptor CCR2 by one or more of the chemokines CCL2, CCL8 and CCL13. In preclinical and clinical studies, inhibition of CCR2 in pancreatic cancer has shown to decrease tumor progression by blocking recruitment and accumulation of monocytes/macrophages in the tumor microenvironment. Analysis of human pancreatic tumors revealed elevation of both CCL2 and CSF1, which recruit monocytes, as well as the monocyte marker CD14, in advanced pancreatic cancers. Current immunotherapy using checkpoint inhibitors are effective in some tumors, but lack efficacy in immune insensitive cancers, including pancreatic cancer. Here, we report that the inhibition of CCR2 using a small molecule antagonist potentiates anti-PD-1 immunotherapy in a syngeneic, orthotropic mouse model of pancreatic cancer. Our data reveal that blocking CCR2 decreases tumor burden by blocking monocyte infiltration and creating a microenvironment more favorable for CD8 T cells activity, and provide a mechanistic rationale for investigating the combination of a CCR2 antagonist and an immune checkpoint inhibitor in pancreatic cancer. Citation Format: Christine Janson, Heiyoun Jung, Linda Ertl, Shirley Liu, Ton Dang, Yibin Zeng, Antoni Krasinski, Jeff McMahon, Penglie Zhang, Israel Charo, Rajinder Singh, Thomas J. Schall. Inhibition of CCR2 potentiates checkpoint inhibitor immunotherapy in murine model of pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5655. doi:10.1158/1538-7445.AM2017-5655

Pancreatic cancer is an aggressive malignancy with 5 year survival rate of less than 5 percent. The predominant immune cells infiltrating the tumor microenvironment are monocytes/macrophages, which are reported to support tumor growth by suppressing host immune responses to the tumor. Recruitment of monocytes to various tissues, including tumors, is dependent upon activation of the chemokine receptor CCR2 by one or more of the chemokines CCL2, CCL8 and CCL13. In preclinical and clinical studies, inhibition of CCR2 in pancreatic cancer has shown to decrease tumor progression by blocking recruitment and accumulation of monocytes/macrophages in the tumor microenvironment. Analysis of the TCGA genomic database of human pancreatic tumors revealed elevation of both CCL2 and CSF1, which recruit monocytes, as well as the monocyte marker CD14, in advanced pancreatic cancers. Current immunotherapy using checkpoint inhibitors are effective in some tumors, but lack efficacy in immune insensitive cancers, including pancreatic cancer. Here, we report that the inhibition of CCR2 using small molecule antagonist potentiates anti-PD-1/PD-L1 immunotherapy in a syngeneic, orthotopic mouse model of pancreatic cancer. The KCKO pancreatic cancer cell line, which harbors a K-ras mutation, was implanted into the tail of the pancreas, and a small molecule CCR2 antagonist was administered after a stable tumor mass had formed. Tumor weight correlated well with the per cent of circulating monocytes in the peripheral blood, and the CCR2 antagonist significantly decreased the blood monocyte count. Similar to the human tumor stroma, the KCKO mouse tumors were infiltrated with monocytes and macrophages, and CCR2 antagonist treatment decreased the infiltration of monocyte/ macrophage. PD-L1 expressions are found in the human pancreatic tumor microenvironment, but treatment of patients with anti-PD-1 has not been found to have efficacy. Similarly, anti-PD-1 treatment alone was not effective in the murine KCKO model, but combination treatment with a CCR2 antagonist resulted in significantly smaller tumors. Moreover, this effect was completely reversed by depleting CD8 T cells, suggesting that by blocking monocyte/macrophage recruitment, the CCR2 antagonist relieved suppression of the CD8 T cells. We confirmed this hypothesis by demonstrating that cells from the KCKO tumor microenvironment inhibited CD3/CD28-induced proliferation of CD8 T cells in culture, but that this inhibition was not present when the mice had received the CCR2 antagonist. Taken together, these data reveal that blocking CCR2 decreases tumor burden by blocking monocyte infiltration and creating a microenvironment more favorable for CD8 T cells activity, and provide a mechanistic rationale for investigating the combination of a CCR2 antagonist and an immune checkpoint inhibitor in pancreatic cancer. Citation Format: Heiyoun Jung, Linda Ertl, Christine Janson, Thomas Schall, Israel Charo. Inhibition of CCR2 potentiates the checkpoint inhibitor immunotherapy in pancreatic cancer [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A107.

Replication stress causes DNA damage at fragile sites in the genome. DNA damage at telomeres can initiate breakage-fusion-bridge cycles and chromosome instability, which can result in replicative senescence or tumor formation. Little is known about the extent of replication stress or telomere dysfunction in human embryonic stem cells (hESCs). hESCs are grown in culture with the expectation of being used therapeutically in humans, making it important to minimize the levels of replication stress and telomere dysfunction. Here, the hESC line UCSF4 was cultured in a defined medium with growth factor Activin A, exogenous nucleosides, or DNA polymerase inhibitor aphidicolin. We used quantitative fluorescence in situ hybridization to analyze individual telomeres for dysfunction and observed that it can be increased by aphidicolin or Activin A. In contrast, adding exogenous nucleosides relieved dysfunction, suggesting that telomere dysfunction results from replication stress. Whether these findings can be applied to other hESC lines remains to be determined. However, because the loss of telomeres can lead to chromosome instability and cancer, we conclude that hESCs grown in culture for future therapeutic purposes should be routinely checked for replication stress and telomere dysfunction.