CXCR4 and breast cancer: Currently, it remains unclear: 1) which downstream genes of HIF-1α in addition to VEGFA, CXCR4 and LOX are regulated by Parkin to mediate Parkin’s function in suppression of metastasis of breast cancer cells; 2) whether Parkin can regulate different steps of cancer progression in addition to metastasis, such as cell survival, metabolic reprogramming and angiogenesis, through regulation of HIF-1α and its downstream genes; 3) whether Parkin can regulate HIF-1α signaling in other types of cancer in addition to breast cancer.