Labile Heme and Heme Oxygenase-1 Maintain Tumor-Permissive Niche for Endometriosis-Associated Ovarian Cancer

Heme induced progesterone-resistant profiling and promotion of endometriosis in vitro and in vivo

Endometriosis is an estrogen-dependent, progesterone-resistant gynecological disease with an unknown pathogenesis. Compared to women without endometriosis, women with endometriosis have a remarkably high heme level in the peritoneal fluid. To further investigate the pathomechanisms of heme in endometriosis, we aimed to identify the dysregulated expression of heme-trafficking proteins, such as PGRMC1/2 that are also receptors that mediate the non-genomic responses to progesterone, and heme-degrading enzymes between ectopic endometrial stromal cells and their normal counterparts. We found that heme could regulate progesterone receptor-related gene expression. Functional human endometrial stromal cell experiments showed that heme promotes cell proliferation and migration in a heme oxygenase-1-independent manner; moreover, blocking oxidative phosphorylation/ATP generation could abolish these effects of heme in vitro, whereas intraperitoneal hemopexin administration could alleviate heme-triggered ectopic lesions in vivo. Therefore, heme likely mediates the induction of progesterone resistance and simultaneously induces endometriosis via the mitochondrial oxidative phosphorylation pathway.

The dual role and mutual dependence of heme/HO-1/Bach1 axis in the carcinogenic and anti-carcinogenic intersection

INTRODUCTION

In physiological concentrations, heme is nontoxic to the cell and is essential for cell survival and proliferation. Increasing intracellular heme concentrations beyond normal levels, however, will lead to carcinogenesis and facilitate the survival of tumor cells. Simultaneously, heme in an abnormally high quantity is also a potent inducer of tumor cell death, contributing to its ability to generate oxidative stress on the cells by boosting oxidative phosphorylation and suppressing tumors through ferroptosis. During tumorigenesis and progression, therefore, heme works as a double-edged sword. Heme oxygenase 1 (HO-1) is the rate-limiting enzyme in heme catabolism, which converts heme into physiologically active catabolites of carbon monoxide (CO), biliverdin, and ferrous iron (Fe²⁺). HO-1 maintains redox equilibrium in healthy cells and functions as a carcinogenesis inhibitor. It is widely recognized that HO-1 is involved in the adaptive response to cellular stress and the anti-inflammation effect. Notably, its expression level in cancer cells corresponds with tumor growth, aggressiveness, metastasis, and angiogenesis. Besides, heme-binding transcription factor BTB and CNC homology 1 (Bach1) play a critical regulatory role in heme homeostasis, oxidative stress and senescence, cell cycle, angiogenesis, immune cell differentiation, and autoimmune disorders. Moreover, it was found that Bach1 influences cancer cells' metabolism and metastatic capacity. Bach1 controls heme level by adjusting HO-1 expression, establishing a negative feedback loop.

MATERIALS AND METHODS

Herein, the authors review recent studies on heme, HO-1, and Bach1 in cancer. Specifically, they cover the following areas: (1) the carcinogenic and anticarcinogenic aspects of heme; (2) the carcinogenic and anticarcinogenic aspects of HO-1; (3) the carcinogenic and anticarcinogenic aspects of Bach1; (4) the interactions of the heme/HO-1/Bach1 axis involved in tumor progression.

CONCLUSION

This review summarized the literature about the dual role of the heme/HO-1/Bach1 axis and their mutual dependence in the carcinogenesis and anti-carcinogenesis intersection.