Background: Programmed cell death protein-1 (PD-1) and its ligands, PD-L1 and PD-L2, constitute a central immune checkpoint pathway that regulates T-cell activity and tumor immune escape, while their relationship with STAT signaling remains incompletely understood in ccRCC. Methods: We analyzed 27 paired ccRCC and adjacent non-tumorous human kidney tissue samples. mRNA levels of PD-1, PD-L1, PD-L2, STAT1, and STAT3 were quantified by RT-qPCR. In addition, representative human ccRCC cell lines (CAKI-2 and A-498) were treated with IFN-γ to assess the time-dependent modulation of immune checkpoint molecules and STAT pathway activation. Results: PD-L1 and PD-L2 were significantly upregulated in tumor tissues compared with adjacent normal kidney tissue. Exploratory observation suggests grade dependent increase. Whereas PD-1 was predominantly downregulated, IFN-γ treatment induced a rapid transcriptional upregulation of PD-L1 and PD-L2 in RCC cell lines, with maximal protein accumulation observed at 72 h. STAT1, but not STAT3, exhibited dynamic induction following IFN-γ stimulation, showing temporal association with PD-L1 and PD-L2 upregulation, indicating cell-line-specific regulatory effects. Correlation analyses confirmed a strong correlation between PD-1 and its ligands, whereas STAT1 and STAT3 expression showed no direct association with PD-L1 or PD-L2 levels in cancer samples. Conclusions: Our findings demonstrate that PD-L1 and PD-L2 are frequently upregulated in ccRCC and dynamically regulated by IFN-γ/STAT1-dependent signaling. Our results provide additional insight into the mechanisms of immune escape and underscore the potential of integrated profiling of PD-1 ligands and STAT signaling to guide personalized immunotherapeutic strategies in ccRCC.

Renal cell carcinoma (RCC) is frequently resistant to tyrosine kinase inhibitors (TKIs) such as sunitinib, limiting therapeutic efficacy. ATP-binding cassette (ABC) transporters, including ABCB1, ABCB5, and ABCG2, are important transporters implicated in multidrug resistance, influencing drug efflux and tumor progression. We aimed to evaluate the expression of ABCB1, ABCB5, and ABCG2 in human RCC tissues and human renal cancer cell lines CAKI-2 and A-498, and to investigate their potential association with sunitinib resistance and associated signaling pathways. Twenty paired tumorous and adjacent non-tumorous human kidney tissue samples were analyzed for ABC transporter gene expression using qRT-PCR. RCC cell lines CAKI-2 and A-498, including sunitinib-resistant derivatives, were treated with 40 µM sunitinib. The levels of transporters and key signaling proteins were assessed by Western blot. ABCG2 was consistently higher in tumorous tissues, and ABCB1 and ABCB5 showed grade-dependent increases in tumors. Resistant cells exhibited elevated ABCB1 and dynamic ABCB5 and ABCG2 expression patterns compared to sensitive cells, indicating an association between altered transporter expression and the resistant phenotype. Sunitinib treatment modulated signaling pathways, with differential activation of PI3K/Akt, NF-κB, and MAPK/ERK observed in sensitive versus resistant cells. Our findings suggest that altered ABCB1 and ABCG2 expression may be associated with the development of sunitinib resistance in RCC and may be linked to changes in key survival signaling pathways. These findings provide a basis for future functional studies investigating the role of ABC transporters in sunitinib resistance and may contribute to the development of personalized therapeutic strategies in RCC.