Expression and significance of hypoxia-inducible factor-1 alpha and MDR1/P-glycoprotein in human colon carcinoma tissue and cells

Hypoxia in tumors is generally associated with chemoresistance and radioresistance. However, the correlation between the heterodimeric hypoxia-inducible factor-1 (HIF-1) and the multidrug resistance (MDR1) gene/transporter P-glycoprotein (P-gp) has not been clearly investigated. This study aims at examining the expression levels of HIF-1 alpha and MDR1/P-gp in human colon carcinoma tissues and cell lines (HCT-116, HT-29, LoVo, and SW480) and ascertaining whether HIF-1 alpha plays an important role in tumor multidrug resistance with MDR1/P-gp. The expression and distribution of HIF-1 alpha and P-gp proteins were detected in human colon carcinoma tissues and cell lines by immunohistochemistry and immunocytochemistry using streptavidin/peroxidase (SP) and double-label immunofluorescence methods. HIF-1 alpha and MDR1 mRNA expression levels in cell lines were analyzed using RT-PCR under normoxic and hypoxic conditions, respectively. The immunohistochemical method shows that HIF-1 alpha and P-gp expression were not correlated with gender, age, location, and differentiation degree (P > 0.05). However, the expression of HIF-1 alpha and P-gp at different Dukes' stages and whether involved in lymphatic invasion shows a significant difference (P < 0.05). Correlation analysis displays that HIF-1 alpha protein expression was correlated significantly with P-gp expression (P < 0.01). Double-label immunofluorescence demonstrates that coexpression of HIF-1 alpha and P-gp does exist in human colon carcinoma tissues. The mRNA expression of HIF-1 alpha and MDR1 was detected in the four human colon carcinoma cell lines under both normoxia and hypoxia. Optical density values representing mRNA expression levels of HIF-1 alpha and MDR1 were found to be significantly higher in the same type cells under hypoxic conditions than that under normoxic conditions, respectively (P < 0.01). However, no significant differences of HIF-1 alpha or MDR1 mRNA expression were found among these cell lines, which exposed under the same PaO2 cultural conditions (P > 0.05). And the immunocytochemistry results were corresponding with the analysis of mRNA expression. These results suggest that hypoxia induce the expression of HIF-1 alpha and MDR1/P-gp in colon carcinoma and HIF-1 alpha expression may be associated with the gene MDR1 (P-gp) and interactively involved in the occurrence of tumor multidrug resistance.