Inorganic phosphate induces cancer cell mediated angiogenesis dependent on forkhead box protein C2 (FOXC2) regulated osteopontin expression

Abstract

Recent studies in both rodents and humans suggest that elevated serum phosphorus, in the context of normal renal function, potentiates or exacerbates pathologies associates with cardiovascular disease, bone metabolism, and cancer. Our recent microarray studies identified the potent stimulation of pro-angiogenic genes such as Forkhead box protein C2 (FOXC2), osteopontin, and Vegfα, among others in response to elevated inorganic phosphate (Pi). Increased angiogenesis and neovascularization are important events in tumor growth and the progression to malignancy and FOXC2 has recently been identified as a potential transcriptional regulator of these processes. In this study we addressed the possibility that a high Pi environment would increase the angiogenic potential of cancer cells through a mechanism requiring FOXC2. Our studies utilized lung and breast cancer cell lines in combination with the human umbilical vascular endothelial cell (HUVEC) vessel formation model to better understand the mechanism(s) by which a high Pi environment might alter cancer progression. Exposure of cancer cells to elevated Pi stimulated expression of FOXC2 and conditioned medium from the Pi-stimulated cancer cells stimulated migration and tube formation in the HUVEC model. Mechanistically, we define the requirement of FOXC2 for Pi-induced OPN expression and secretion from cancer cells as necessary for the angiogenic response. These studies reveal for the first time that cancer cells grown in a high Pi environment promote migration of endothelial cells and tube formation and in so doing identify a novel potential therapeutic target to reduce tumor progression.

Dysregulation of phosphate metabolism and conditions associated with phosphate toxicity

“…89 Just as tumorigenesis in tomato plants has been positively associated with phosphorus, 90 a cellular environment high in phosphorus in humans has been found to induce tumor neovascularization and angiogenesis, or new blood vessel formation in neoplasms. 91 Dietary phosphorus overload has been found to stimulate tumor growth in lung tissue. 92 Increasing phosphorus levels in cultured breast cancer cells were observed to change cellular behavior and metabolism, thus supporting the role of inorganic phosphate in modulating tumor metabolism and metastasis.…”

Biological effects of inorganic phosphate: potential signal of toxicity

“…In response to Pi treatment, the respective expression levels of forkhead box protein C2 (FOXC2), osteopontin (OPN), and vascular endothelial growth factor alpha (VEGFα) increased (Lin et al, 2014). FOXC2, a transcription factor, is necessary for vascular development (Seo et al, 2006).…”

Elevated FOXC2 Expression Promotes Invasion of HCC Cell Lines and is Associated with Poor Prognosis in Hepatocellular Carcinoma

“…Accumulating evidence has shown that FOXC2 is involved in tumor cell proliferation, invasion, differentiation, and cisplatin-resistance [12-15]. In extrahepatic cholangiocarcinoma, FOXC2 acts as an oncogene by regulating the ability to migrate and invade with concomitant upregulation of N-cadherin, MMP-2 and Ang-2, and high FOXC2 expression is associated with a shorter duration of recurrence-free survival and poor prognosis [13].…”