Overexpression of integrin-associated protein (CD47) in rat kidney treated with a renal carcinogen, ferric nitrilotriacetate.

An iron chelate, ferric nitrilotriacetate (Fe-NTA), induces renal proximal tubular necrosis, a consequence of free radical-associated damage, that ultimately leads to a polycystic change of the renal cortex and a high incidence of renal cell carcinoma (RCC) in rodents. The differential display technique was used to search for inducible genes in the kidney of male Wistar rats treated with Fe-NTA and in the induced RCCs. Six fragments were selected that showed specific quantitative changes in mRNA. Two of them exhibited similar patterns in northern blots as well. One fragment showed a high homology (89%) to murine integrin-associated protein (IAP; CD47). We thus cloned rat IAP cDNA including the entire coding region for use in further analysis. Rat IAP cDNA showed a 21-amino-acid deletion that was also observed in human, but not in mouse. Northern blots revealed that IAP was consistently overexpressed in non-tumorous parts of the kidney (2.4-fold increase, n = 9, P < 0.0001) as compared with matched controls 1 to 2 years after Fe-NTA treatment. IAP overexpression of more than 2.9-fold was found in 25% (2/8) of RCCs studied, and was limited to cases of a high histological grade and lung metastasis. Unexpectedly, IAP expression was higher in the non-tumorous part of the kidney after Fe-NTA treatment (2.8-fold) than in RCC (1.5-fold) in each case (n = 4, P < 0.05). Abundant expression of IAP mRNA in the renal tubular epithelium after Fe-NTA treatment and RCC cells was observed by in situ hybridization. The results suggest that IAP overexpression may be associated with Fe-NTA-induced renal cortical tubular damage and regeneration that lead to a polycystic state, and with tumor progression and metastasis of the induced RCCs.