IL-33 increases ST2⁺ Tregs and promotes metastatic tumour growth in the lungs in an amphiregulin-dependent manner

ABSTRACT

Regulatory T cells (Tregs) facilitate primary and metastatic tumour growth through the suppression of anti-tumour immunity. Emerging evidence suggests a distinct role for Tregs in mediating tissue repair and barrier integrity in the lungs by IL-33 mediated production of the growth factor amphiregulin (AREG). Dependent on the type of cancer and local microenvironment, AREG may induce tumour cell proliferation, invasion, migration or resistance to apoptosis by signaling through the epidermal growth factor receptor (EGFR). We have found that IL-33 is dramatically increased in and around metastatic tumour foci in the lungs of mice bearing orthotopic murine mammary tumours. We observed that Tregs express significantly more of the IL-33 receptor, ST2, relative to conventional T cells, that ST2⁺ Tregs accumulate in the lungs of metastatic tumour-bearing mice, and that ST2⁺ Tregs produce significantly more AREG than ST2⁻ Tregs. The intranasal administration of recombinant IL-33 increased the proportion of AREG producing ST2⁺ Tregs and enhanced the level of phosphorylated EGFR in the metastatic lungs. While recombinant AREG did not impact mammary tumour cell proliferation in vitro despite inducing a dose-dependent increase in phosphorylated EGFR, intranasal administration of AREG resulted in a ten-fold increase in pulmonary metastatic tumour burden in vivo. Further, the intranasal administration of recombinant IL-33 significantly increased metastatic tumour burden in the lungs in an amphiregulin-dependent manner. These data identify ST2⁺ Tregs as a microenvironmental source of AREG in the lungs of mice with orthotopic metastatic mammary tumours and highlight an important role for AREG in promoting metastatic tumour growth in the lungs.

KEYWORDS:

• Regulatory T cells
• ST2
• IL-33
• amphiregulin
• metastasis
• breast cancer

Acknowledgments

The authors would like to thank Dr. Meegan Larsen, DVM, DVSc from MBed Pathology for expert pathological analysis of mouse lung tissue samples, and Anita Carraro for assistance with slide imaging. Additionally, the authors would like to thank Avery Lam and Dr. Megan Levings for protocols and helpful discussions.

Disclosure statement

The authors declare no conflict of interest or financial disclosures.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This research was funded by the CURE Foundation and the Cancer Research Society [21441; KLB] and the Canadian Institutes of Health Research [MOP-126138 to KLB and MOP-142313 to WWL/KLB]. ECH is funded by a Four Year Doctoral Fellowship and by a Li Tze Fong Memorial Fellowship from the University of British Columbia. BJW is funded by a Canadian Institutes of Health Research (CIHR) Doctoral Research Award. RAC is funded by a Frederick Banting and Charles Best Canada Graduate Scholarship from CIHR. KLB and WWL are Michael Smith Foundation for Health Research Biomedical Research Scholars.