Gas6/MerTK signaling is negatively regulated by NF-κB and supports lung carcinogenesis

// Sergey V. Novitskiy 1 , * , Rinat Zaynagetdinov 1 , * , Georgii Vasiukov 1 , Sergey Gutor 1 , Wei Han 1 , Ana Serezani 1 , Anton Matafonov 2 , Linda A. Gleaves 1 , Taylor P. Sherrill 1 , Vasiliy V. Polosukhin 1 and Timothy S. Blackwell 1 , 3 , 4 1 Division of Allergy, Pulmonary and Critical Care Medicine, Department of Medicine, Vanderbilt University, Nashville, TN, 37212, USA 2 Department of Pathology, Microbiology, and Immunology, Vanderbilt University, Nashville, TN, 37212, USA 3 Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN, 37212, USA 4 Department of Veterans Affairs Medical Center, Nashville, TN, 37212, USA * These authors contributed equally to this work Correspondence to: Sergey V. Novitskiy, email: sergey.v.novitskiy@vumc.org Keywords: lung cancer; NF-κB; Mer-TK; macrophage; Kras Received: August 06, 2019     Accepted: November 07, 2019     Published: December 17, 2019 ABSTRACT Growth arrest-specific 6 (Gas6) has been implicated in carcinogenesis through activation of its receptors, particularly MerTK. To investigate whether Gas6 plays a role in resistance to NF-κB inhibitors, which have not proven to be effective agents for lung cancer therapy, we studied lung cancer models induced by urethane injection or expression of mutant Kras (Kras G12D ). We found that Gas6 is primarily produced by macrophages during tumorigenesis and that Gas6 is negatively regulated by NF-κB. Since Gas6 is a vitamin K dependent protein, we used low-dose warfarin to block Gas6 production and showed that this treatment inhibited tumorigenesis in both the urethane and Kras G12D models, most prominently in mice with targeted deletion of IKKβ in myeloid cells (IKKβ ΔMye mice). In addition, MerTK deficient mice had reduced urethane-induced tumorigenesis. Inhibition of the Gas6-MerTK pathway in all these models reduced macrophages and neutrophils in the lungs of tumor-bearing mice. Analysis of mouse lung tumors revealed MerTK staining on tumor cells and in vitro studies showed that Gas6 increased proliferation of human lung cancer cell lines. To assess the therapeutic potential for combination treatment targeting NF-κB and Gas6-MerTK, we injected Lewis Lung Carcinoma cells subcutaneously and treated mice with Bay 11-70852 (NF-κB inhibitor) and/or Foretinib (MerTK inhibitor). While individual treatments were ineffective, combination therapy markedly reduced tumor growth, blocked tumor cell proliferation, reduced tumor-associated macrophages, and increased CD4+ T cells. Together, our studies unmask a role for Gas6-MerTK signaling in lung carcinogenesis and indicate that up-regulation of Gas6 production in macrophages could be a major mechanism of resistance to NF-κB inhibitors.