Poster abstracts

Poster number 62 submitted by Mary Forget

HIF-1α, but not HIF-2α, Regulates TIE2-Expressing Monocyte Recruitment to PyMT Breast Tumors

Mary Forget (1Division of Pulmonary, Allergy, Critical Care, Sleep Medicine, Department of Internal Medicine; 2 Molecular, Cellular, Developmental Biology Program The Ohio State University, Columbus, Ohio 43210), Timothy Eubank (1Division of Pulmonary, Allergy, Critical Care, Sleep Medicine, Department of Internal Medicine; 2 Molecular, Cellular, Developmental Biology Program The Ohio State University, Columbus, Ohio 43210), Clay Marsh (1Division of Pulmonary, Allergy, Critical Care, Sleep Medicine, Department of Internal Medicine; 2 Molecular, Cellular, Developmental Biology Program The Ohio State University, Columbus, Ohio 43210)

Abstract:
Tie2 is a tyrosine kinase receptor first described on vascular endothelial cells. Activation of the Tie2 receptor by its ligands, Angiopoietin-1 and -2 (Ang-1 and -2) modulate blood vessel growth and function. Hypoxia is known to increase expression of the Tie2 receptor on human endothelial cells and the Hypoxia Inducible Factor proteins (HIFs) have been implicated in the regulation of this process. Recently, it has been shown that approximately seven percent of circulating human monocytes express the Tie2 receptor. Tie2-expressing monocytes (TEMs) are reported to migrate into tumors and regulate angiogenesis and metastasis. Hypoxia has been linked to TEM recruitment but specific regulation of this process has not been defined. In this study, we elucidate the roles of HIF-1α and HIF-2α, specifically, in the expression of the Tie2 receptor on these TEMs and the effect of their absence in PyMT mouse model of breast cancer. To investigate Tie2 receptor expression on monocytes in vitro, human monocytes were incubated for 48 hours at normoxia or hypoxia (0.5% oxygen), labeled with an antibody specific for Tie2 expression, and analyzed by flow cytometry. We found that 27.9% of wild type CD14+ monocytes were Tie2 receptor positive at hypoxia compared to 15.1% at normoxia. To examine the effect of HIF-1α and HIF-2α deficiency on TEMS, we used control, or HIF-1αflox/floxLysMcre or HIF-2αflox/floxLysMcre mice where the HIF protein is deficient in cells from the macrophage compartment. In vivo, we found that TEMs constituted 8% of the total tumor CD11b+ monocytes in the HIF-1αflox/floxLysMcre mice, significantly reduced from the 34% of the total CD11b+ monocytes in tumors from the wild type mice and 36% total CD11b+ monocytes from the HIF-2αflox/floxLysMcre mice. Phenotypically, tumors from the HIF-1αflox/floxLysMcre mice grew slower and displayed less angiogenesis compared to tumors from both wild type mice and HIF-2αflox/floxLysMcre mice as shown by CD31 staining.

Keywords: Monocytes, TEM, Breast Cancer