Micronuclei in Kif18a mutant mice form stable micronuclear envelopes and do not promote tumorigenesis

Micronuclei, whole or fragmented chromosomes spatially separated from the main nucleus, are associated with genomic instability and have been identified as drivers of tumorigenesis. Paradoxically, Kif18a mutant mice produce micronuclei due to asynchronous segregation of unaligned chromosomes in vivo but do not develop spontaneous tumors. We report here that micronuclei in Kif18a mutant mice form stable nuclear envelopes. Challenging Kif18a mutant mice via deletion of the Trp53 gene led to formation of thymic lymphoma with elevated levels of micronuclei. However, loss of Kif18a had modest or no effect on survival of Trp53 homozygotes and heterozygotes, respectively. Micronuclei in cultured KIF18A KO cells form stable nuclear envelopes characterized by increased recruitment of nuclear envelope components and successful expansion of decondensing chromatin compared with those induced by nocodazole washout or radiation. Lagging chromosomes were also positioned closer to the main chromatin masses in KIF18A KO cells. These data suggest that not all micronuclei actively promote tumorigenesis.

Discriminating Spontaneous From Cigarette Smoke and THS 2.2 Aerosol Exposure-Related Proliferative Lung Lesions in A/J Mice by Using Gene Expression and Mutation Spectrum Data

Mice, especially A/J mice, have been widely employed to elucidate the underlying mechanisms of lung tumor formation and progression and to derive human-relevant modes of action. Cigarette smoke (CS) exposure induces tumors in the lungs; but, non-exposed A/J mice will also develop lung tumors spontaneously with age, which raises the question of discriminating CS-related lung tumors from spontaneous ones. However, the challenge is that spontaneous tumors are histologically indistinguishable from the tumors occurring in CS-exposed mice. We conducted an 18-month inhalation study in A/J mice to assess the impact of lifetime exposure to Tobacco Heating System (THS) 2.2 aerosol relative to exposure to 3R4F cigarette smoke (CS) on toxicity and carcinogenicity endpoints. To tackle the above challenge, a 13-gene gene signature was developed based on an independent A/J mouse CS exposure study, following by a one-class classifier development based on the current study. Identifying gene signature in one data set and building classifier in another data set addresses the feature/gene selection bias which is a well-known problem in literature. Applied to data from this study, this gene signature classifier distinguished tumors in CS-exposed animals from spontaneous tumors. Lung tumors from THS 2.2 aerosol-exposed mice were significantly different from those of CS-exposed mice but not from spontaneous tumors. The signature was also applied to human lung adenocarcinoma gene expression data (from The Cancer Genome Atlas) and discriminated cancers in never-smokers from those in ever-smokers, suggesting translatability of our signature genes from mice to humans. A possible application of this gene signature is to discriminate lung cancer patients who may benefit from specific treatments (i.e., EGFR tyrosine kinase inhibitors). Mutational spectra from a subset of samples were also utilized for tumor classification, yielding similar results. “Landscaping” the molecular features of A/J mouse lung tumors highlighted, for the first time, a number of events that are also known to play a role in human lung tumorigenesis, such as Lrp1b mutation and Ros1 overexpression. This study shows that omics and computational tools provide useful means of tumor classification where histopathological evaluation alone may be unsatisfactory to distinguish between age- and exposure-related lung tumors.

Micronuclei arising due to loss of KIF18A form stable micronuclear envelopes and do not promote tumorigenesis

Micronuclei, whole or fragmented chromosomes which are spatially separated from the main nucleus, are strongly associated with genomic instability and have been identified as drivers of tumorigenesis. Paradoxically, Kif18a mutant mice produce micronuclei due to unaligned chromosomes in vivo but do not develop spontaneous tumors, raising questions about whether all micronuclei contribute similarly to genomic instability and cancer. We report here that micronuclei in Kif18a mutant mice form stable nuclear envelopes. Challenging Kif18a mutant mice via deletion of the Trp53 gene led to formation of thymic lymphoma with elevated levels of micronuclei. However, loss of Kif18a had modest or no effect on survival of Trp53 homozygotes and heterozygotes, respectively. To further explore micronuclear envelope stability in KIF18A KO cells, we compared micronuclei induced via different insults in cultured cells. Micronuclei in KIF18A KO cells form stable nuclear envelopes characterized by increased recruitment of core and non-core nuclear envelope components and successful expansion of decondensing chromatin compared to those induced by microtubule drug washout or exposure to radiation. We also observed that lagging chromosomes, which lead to micronucleus formation, were positioned closer to the main chromatin masses, and further from the central spindle, in KIF18A KO cells. Our studies provide in vivo support to models suggesting that micronuclear fate depends on the sub-cellular location of late lagging chromosomes and suggest that not all micronuclei actively promote tumorigenesis.

L1 TGF-beta blocks type I IFN release and tumor rejection in spontaneous mammary tumors

BackgroundActivation of the STimulator of INterferon Genes (STING) by DMXAA (5,6-dimethylxanthenone-4-acetic acid) can induce a strong production of IFNα/β and the rejection of transplanted primary tumors. However, the efficacy of such therapeutic approach for the treatment of spontaneous tumors had still to be evaluated.Material and MethodsWe have tested whether the injection of DMXAA or other STING agonists and TLR4 agonist, could lead to the regression of spontaneous MMTV-PyMT mammary tumors. We also characterized, in time and space, the early signaling events triggered downstream STING and the distribution of infiltrating immune cells in the tumor microenvironment by fluorescence imaging.ResultsWe show that spontaneous MMTV-PyMT mammary tumors are resistant to immunotherapeutic intervention. We demonstrate that TGFβ, abundant in spontaneous tumors, is a key molecule limiting this IFN-induced-tumor regression by DMXAA. Mechanistically, we found that TGFβ blocks the phosphorylation of IRF3 and the ensuing IFNα/β production by tumor infiltrating macrophages. Finally, blocking TGFβ restores the production of IFNα by activated MHCII+ tumor-associated macrophages, and enables tumor regression induced by STING activation.ConclusionsBased on these findings, we propose that the efficacy of many cancer therapies, which are type I IFN-dependent, should be greatly improved by combination with TGFβ blockade.Disclosure InformationN. Bercovici: None. M.V. Guérin: None. F. Regnier: None. J.M. Weiss: None. V. Feuillet: None. L. Vimeux: None. G. Altan-Bonnet: None. E. Donnadieu: None. A. Trautmann: None.

TGFβ blocks IFNα/β release and tumor rejection in spontaneous mammary tumors

Type I interferons (IFN) are being rediscovered as potent anti-tumoral agents. Activation of the STimulator of INterferon Genes (STING) by DMXAA (5,6-dimethylxanthenone-4-acetic acid) can induce strong production of IFNα/β and rejection of transplanted primary tumors. In the present study, we address whether targeting STING with DMXAA also leads to the regression of spontaneous MMTV-PyMT mammary tumors. We show that these tumors are refractory to DMXAA-induced regression. This is due to a blockade in the phosphorylation of IRF3 and the ensuing IFNα/β production. Mechanistically, we identify TGFβ, which is abundant in spontaneous tumors, as a key molecule limiting this IFN-induced tumor regression by DMXAA. Finally, blocking TGFβ restores the production of IFNα by activated MHCII+ tumor-associated macrophages, and enables tumor regression induced by STING activation. On the basis of these findings, we propose that type I IFN-dependent cancer therapies could be greatly improved by combinations including the blockade of TGFβ.

A Comparison of Spontaneous Tumors in Tg.rasH2 Mice in 26-week Carcinogenicity Studies Conducted at a Single Test Facility during 2004 to 2012 and 2013 to 2018

This article presents the historical control data of spontaneous tumors in Tg.rasH2 published in 2013 (2004–2012) and compares and contrasts it to more recent data collected from 2013 to 2018, reporting differences in the average percentage incidences or incidence ranges as well as the incidence of new tumors. In 2013, we published a comprehensive review of spontaneous tumors in Tg.rasH2 mice used in 26-week carcinogenicity studies, which included data from control dose groups from 26 studies and a total of 710 mice per sex. The total database, now including the more recent data, has nearly doubled the number of animals, completing to date a total of 52 studies in males and 51 studies in females for a total of 1,615 male mice and 1,560 female mice, respectively. In this article, we compare the data collected from 2004 to 2012 against the data collected from 2013 to 2018 and the overall tumor incidence change.