Hypoxia Inducible Factor-Alpha Promotes Expression of Pro-tumorigenic Semaphorin7A in Mammary Tumor Cells

It is estimated that one in eight women will be diagnosed with breast cancer. Developing an
understanding of the tumor microenvironment is critical for developing treatments for breast cancer
patients. It has been well established that hypoxia, or a lack of oxygen, is fundamental in creating a
microenvironment that enables metastasis via eliciting angiogenic processes. Poorly differentiated blood
vessels can fashion an oxygen-deprived microenvironment that triggers the expression of transcription
factor Hypoxia Inducible Factor alpha HIF-1alpha that in turn can up regulate genes mediating a protumor
effect. Our laboratory has discovered that mammary tumors express Semaphorin7a SEMA7A, a
HIF-1alpha inducible protein. This study’s objective is to delineate the mechanism for hypoxia induction
in mammary cells. Cobalt Chloride CoCl2 was used to mimic hypoxia in mammary tumor cell cultures.
Flow cytometry was used to determine HIF-1alpha activity in the mammary cells. Benign EpH4 mammary
cells expressing low SEMA7A greatly increased its expression after response to hypoxic stimuli as
determined by qPCR and SEMA7A-specific ELISA. Pretreatment of EpH4 cells with a HIF-1alpha
inhibitor Chemotin blocked induction of SEMA7A. Paradoxically, CoCl2 did not raise expression in the
highly metastatic 4T1 cells which experience high levels of SEMA7A. Treatment of 4T1 cells with
Chemotin under normoxic conditions inhibit HIF-1alpha activity and decrease SEMA7A levels.
Determining the role of SEMA7A in the hypoxia axis could further elucidate novel pathways in breast
cancer, suggesting that malignant tumor cells can utilize HIF-1alpha in a hypoxic independent manner.