The activation and recruitment of the small GTPase Rab7 to early endosome is a critical step for early to late endosome maturation, a process that requires the class III phosphatidylinositol 3-kinase (PI3KC3) and GTPase regulators. However, the molecular mechanism underlying Rab7 activation and endosome maturation is still poorly defined. Here we report that Rubicon, a component of the PI3KC3 complex, prevents endosome maturation through differential interactions with Rab7 and UVRAG. UVRAG activates PI3KC3 and C-VPS/HOPS, a guanine nucleotide exchange factor that catalyzes the exchange of GDP for GTP on Rab7. We demonstrate that Rubicon sequesters UVRAG from C-VPS/HOPS. Active GTP-bound Rab7 competes for Rubicon binding and releases UVRAG to associate with C-VPS/HOPS, which in turn promotes further loading of Rab7 with GTP. This feed-forward loop ensures rapid amplification of GTP-bound Rab7 and consequent stimulation of endosome maturation. Hence, Rubicon serves as a previously unknown Rab7 effector to ensure the proper progression of the endocytic pathway.autophagy | endocytosis | epidermal growth factor | autophagosome | Barkor/Atg14(L)

Summary Although oncogene-targeted therapy often elicits profound initial tumor responses in patients, responses are generally incomplete because some tumor cells survive initial therapy as residual disease that enables eventual acquired resistance. The mechanisms underlying tumor cell adaptation and survival during initial therapy are incompletely understood. Here, through the study of EGFR-mutant lung adenocarcinoma we show that NF-κB signaling is rapidly engaged upon initial EGFR inhibitor treatment to promote tumor cell survival and residual disease. EGFR oncogene inhibition induced an EGFR-TRAF2-RIP1-IKK complex that stimulated an NF-κB-mediated transcriptional survival program. The direct NF-κB inhibitor PBS-1086 suppressed this adaptive survival program and increased the magnitude and duration of initial EGFR inhibitor response in multiple NSCLC models, including a patient-derived xenograft. These findings unveil NF-κB activation as a critical adaptive survival mechanism engaged by EGFR oncogene inhibition and provide rationale for EGFR and NF-κB co-inhibition to eliminate residual disease and enhance patient responses.

BackgroundImmune checkpoint inhibitors have transformed the treatment landscape for many cancers, including metastatic melanoma, but have also opened the door for a diverse variety of immune-related adverse effects.Case presentationWe describe the first reported case of presumed neurosarcoidosis as an immune-related adverse effect that developed nearly a year after discontinuation of treatment with combination ipilimumab and nivolumab for recurrent metastatic melanoma. The patient was noted to develop clinical signs consistent with systemic sarcoidosis shortly after the initiation of treatment and underwent a biopsy of hilar lymphadenopathy that confirmed sarcoidosis and after which immunotherapy was discontinued. His melanoma remained stable on surveillance imaging for the next year after which time he developed neurological symptoms and was found to have MRI brain abnormalities without evidence of intracranial metastatic disease, consistent with probable neurosarcoidosis given biopsy-proven systemic sarcoidosis and lack of evidence of CNS infection or malignancy. He underwent treatment with high dose steroids, followed by infliximab, and then methotrexate with both clinical and radiographic improvement within 4 months of starting treatment.ConclusionsImmune-related adverse effects often occur within 3–6 months of receiving immune checkpoint inhibitor therapy, with some reports of late toxicity. This report highlights a case of probable neurosarcoidosis nearly a year after discontinuation of immune checkpoint therapy. The potential for durable responses after discontinuation of therapy also likely underscores a potential for late toxicity. In patients presenting with new or unexplained symptoms after checkpoint inhibitor therapy, the index of suspicion for an immune-related adverse effect should remain high, irrespective of timing.