C‐terminal polycystin‐1 (PC1) peptide stimulates interleukin‐8 expression

Abstract

We have reported that Interleukin-8 (IL-8, a growth and angiogenic factor in cancer cells) as well as its receptors are constitutively expressed by autosomal dominant polycystic kidney disease (ADPKD) cyst cells (cc), suggesting a role of IL-8 in angiogenesis and cyst-cell growth. We hypothesized that PC1 (the gene product of PKD1 whose mutations accounts for most of ADPKD cases) directly regulates IL-8 expression in ADPKD cyst cells. We study the expression of IL-8 and its transcription factors and, since PC1 regulates signaling pathways, including JNK/AP1 activation, we tested whether the C-terminal 200 amino acids of PC1 (P200) activates the IL-8 promoter. Consistent with our previous findings, IL-8 mRNA and protein levels were higher in primary cultures of ADPKD cc than in human proximal tubule (HPT) cells. Total mRNA of the transcriptional factor for IL-8 expression NFκB was similar in ADPKDcc and HPT cells, whereas for nuclear-factor IL-6 was higher in ADPKDcc and for c-Jun was higher in HPT cells. However, by immunohistochemistry, phosphorylated cJun was higher in ADPKD kidneys than that in normal kidney, suggesting activation of AP1. P200 was transiently cotransfected with expression vectors containing either the core promoter of IL-8 or multiple AP1 binding sites in COS-7, HEK293, CHO-k1 and MDCK cells. We found that P200 stimulated both the IL-8 promoter and the promoter containing the AP1 binding sites in all the cells tested except HEK293. Activation was cell-specific, the strongest in CHO-k1 cells. These findings indicate that the C-terminal domain of PKD1 activates IL-8 via AP1, thus establishing the existence of an additional mechanism of ADPKD cyst cell growth. Supported by AHA Grant.