IN VIVO ANALYSIS OF THE ROLE OF GASDERMIN-B (GSDMB) IN CANCER USING NOVEL KNOCK-IN MOUSE MODELS

Background Gasdermin-B gene (GSDMB) is frequently over-expressed in tumors, and its shortest translated variant (isoform 2; GSDMB2) increases aggressive behavior in breast cancer cells. Paradoxically, GSDMB could have either pro-tumor or tumor suppressor properties depending on the biological context. Since GSDMB gene is not present in the mouse genome, deciphering fully the functional roles of GSDMB in cancer requires novel in vivo models. Methods We first generated by gene targeting a conditional knock-in mouse model (R26-STOP-GB2) harboring human GSDMB2 transcript within the ROSA26 locus. We next derived the R26-GB2 model ubiquitously expressing GSDMB2 in multiple tissues (confirmed by western blot and immunohistochemistry) and performed a comprehensive histopathological analysis in multiple tissues from 75 male and female mice up to 18 months of age. Additionally, we produced the double transgenic model R26-GB2/MMTV-PyMT, co-expressing GSDMB2 and the Polyoma-Middle-T oncogene, and assessed breast cancer generation and progression in GSDMB2-homozygous (n=10) and control (n=17) female mice up to 15 weeks of age. Results In the R26-GB2 model, which showed different GSDMB2 cytoplasmic and/or nuclear localization among tissues, we investigated if GSDMB2 expression had intrinsic tumorigenic activity. 41% of mice developed spontaneous lung tumors, but neither the frequency nor the histology of these neoplasias was significantly different from wildtype animals. Strikingly, while 17% control mice developed gastric carcinomas, no GSDMB2-positive mice did. No other tumor types or additional histological alterations were frequently seen in these mice. In the R26-GB2/MMTV-PyMT model, the strong nucleus-cytoplasmic GSDMB2 expression in breast cancer cells did not significantly affect cancer formation (number of tumors, latency, tumor weight, histology or proliferation) or lung metastasis potential compared to controls. Conclusions GSDMB2 expression alone does not have an overall tumorigenic potential in mice, but it might reduce gastric carcinogenesis. Contrary to human cancers, GSDMB2 upregulation does not significantly affect breast cancer generation and progression in mouse models. However, to evidence the GSDMB functions in cancer and other pathologies in vivo may require the presence of specific stimulus or cellular contexts. Our novel mouse strains will serve as the basis for the future development of more precise tissue-specific and context-dependent cancer models.