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.