Objective Renal papillary cell carcinoma(RPCC) has been historically regarded as a radio-resistant malignancy. However, the molecular mechanism underlying its radio-resistance is not well understood. Recently,STAT1, a transcription factor downstream of the IFN-signalling pathway, has been implicated in radioresistance. This study is to investigate the role of STAT1 in "radio-resistant RPCC". Methods The expression of STAT, in 137 human RPCC samples compared with 15 normal kidney tissues was examined by micrearray expression profiling using the Affymetrix HGU133 Plus 2.0 GeneChip oligonucleotide arrays. For in-vltro experiments, human RPCC cell line(SKRC-39), human fibroblast(CCL-116) and human Wiim's tumor cell line(CRL-1441) were used. Western blotting was performed to evaluate total and phosporylated STAT1 expression. RPCC cells were irradiated and compared to controls in clonogenic assays. STAT1 inhibition either with fludarabine or siRNA was done and their effects on radiation-induced cell survival were investigated. Results The STAT1 expression data shows that there was a significant increase in human RPCC when compared to normal kidney tissues (t=44.38,P=0.000). Similarly, the expression of STAT1 was higher in the RPCC cell line when compared to firbroblast and Wilm's tumor cell lines. STAT1 expression was inhibited by beth fludarabine and siRNA. Radiosensitivity in RPCC cell lines was enhanced by both fludarabine and siRNA induced STAT1 inhibition. Conclusions This is the first study reporting the over-expression of STAT1 in human RPCC tissues and human RPCC cell line. Radiesensitization of RPCC is observed via inhibition of STAT1 signaling by fludarabine and siRNA techniques. Our data suggests that STAT1, through IFN-signalling pathway , may play a key role in RPCC radioresistance and manipulation of this pathway may enhance the efficacy of radiotherapy.

Objective To study the expression of signal transducer and activator of transcription 1 (STAT1) in human renal clear cell carcinoma (RCC) and the effect of STATI inhibition on the radiosensi-tivity of RCC. Methods The expression of STAT1 in 34 human RCC samples compared with 12 normal kid-ney tissues was examined by immunohistochemistry method. For in vitro experiments, a human RCC cell line, CRL-1932, was used. Western blotting was performed to evaluate the expression of total and phospory-lated STAT1. Fludarabine and siRNA were respectively used to inhibit the expression of STAT1 in CRL-1932 cells. Clonogenic assay and trypan blue staining assay were used to evaluate the radiosensitivity of CRL-1932 cells. Results The expression of both total and phospborylated STAT1 in human RCC samples was signifi-cantly higher when compared to normal kidney tissues. Similarly, the expression of STAT1 was higher in CRL-1932 cells when compared to fibroblast and Wilm's tumor cell lines. STAT1 expression was inhibited by both fludarabine and siRNA. Radiosensitivity of CRL-1932 cells was enhanced by both fludarabine and siRNA induced STAT1 inhibition. Conclusions STAT1 is over-expressed in both human RCC tissue and cell line. Inhibition of STAT1 can enhance the radiosensitivity of RCC cells.