Regulation of tumor growth and angiogenesis in colorectal cancer

Abstract

Hypoxia in malignant tissues is associated with poor prognosis and treatment options. It is obvious that the grade of malignancy is associated with dedifferentiation of a given tissue. Our aim was to assess the expression of proteins that act as cellular oxygen sensors, which directly regulate the hypoxia-inducible factor 1 (HIF-1) pathway, i.e., prolyl hydroxylase domain proteins (PHD) PHD-1, PHD-2, PHD-3, and its target gene vascular endothelial growth factor (VEGF) in colorectal cancer (CRC). In this study, we cultured a human colon cancer cell line (SW480) and its correspondent lymph-node metastasis cell line (SW620) under normoxic or hypoxic conditions for different time periods. We then measured the HIF-1a expression using Western-Blot, the messenger RNA (mRNA)-expression of the PHDs with real-time polymerase chain reaction (PCR) and the amount of one of the target-genes using an VEGF-ELISA. SW620 shows a clearly elevated HIF-1a expression under normoxic and hypoxic states compared with SW480. Under hypoxic conditions, the amount of VEGF is elevated in both primary and secondary tumor-cell line, but the metastasis-cell line has a significant higher increase. PHD-1 shows no higher expression under hypoxic condition, PHD-2 expression is elevated but only in SW480. PHD-3 levels raised in both of the cell lines, with significant higher rates in SW480. HIF-regulating proteins are highly expressed in CRCs and their metastases. These molecules play an important role in the control of hypoxia-induced genes and may also have a function in the regulation of cellular proliferation and differentiation during tumorigenesis and dedifferentiation of CRCs. Our results emphasize the important role of PHDs not only as an oxygen-sensor, but also as a control-unit for tumor growth, apoptosis, and angiogenesis through HIF-1 pathway.