DIVERSE ROLES OF THE FREE-FATTY ACID RECEPTORS FFA1 AND FFA4 IN PAPILLARY RENAL CELL CARCINOMA CELLS

Abstract

Renal cell carcinoma (RCC) is one of the deadliest genitourinary cancers, and the incidence of RCC has risen steadily. 15-20% of all RCC cases include papillary renal cell carcinoma (pRCC), the most frequent non-clear cell carcinoma subtype, which displays distinct molecular, genetic, and histological characteristics compared to the clear cell RCC (ccRCC). Advanced stage pRCC is highly metastatic and exhibits poor prognosis and the worst outcome compared to patients with ccRCC. Most of the clinical and pre-clinical studies on RCC were conducted on ccRCC, considering ccRCC is the most frequent type of RCC subtype. Therefore, traditional, and newly developed therapeutics are less effective, leaving no optimal treatment available for metastatic patients with pRCC. Therefore, it is crucial to identify novel molecular pathways for a better understanding of pRCC carcinogenesis leading to develop better and more effective pRCC-oriented drug targets. Our study demonstrates for the first time that free-fatty acid receptors 1 (FFA1) and FFA4, G-protein coupled receptors (GPCRs) that endogenously activated by long to medium chain fatty acids are upregulated in human pRCC cancerous tissues compared to matched noncancerous tissues. Moreover, FFA1/FFA4 expression increases as the disease approaches higher pathological T stages. We also reveal that FFA1/FFA4 transcripts are expressed in a well-characterized human pRCC cell line ACHN, but not in primary and metastatic ccRCC cell line 7860 and Caki-1, respectively. Using synthetic agonists and antagonists of FFA1 and FFA4, we showed that FFA1 and FFA4 have opposing effects in pRCC cell growth and motile activities, and astonishingly, they both serve as a “double edge sword” in the regulation of pRCC carcinogenesis. FFA1 positively regulates cell proliferation and tumor formation in pRCC and utilizes the c-Src-mediated PI3K/AKT/NF-κB/COX-2 pathway to promote serum-induced cell proliferation in vitro. On contrary, FFA1 negatively regulates the wound-healing process, migration, invasion, and EMT in ACHN cells. We also demonstrate that FFA1 regulates cell invasion in part by blocking EGFR-mediated ERK1/2 signaling; moreover, FFA1 inhibits STAT3 activation to prevent motile activities in pRCC cells. Unlike FFA1, FFA4 inhibits cell proliferation and c-Src phosphorylation in vitro, as well as reduces tumor growth in vivo. On the other hand, FFA4 promotes wound recovery, migration, invasion, and STAT3-induced EMT. FFA4-induced cell invasion is dependent on ERK1/2 pathways and to some extent on EGFR-mediated ERK1/2 signaling. Moreover, FFA4 increases cell invasion through the activation of PI3K/AKT/NF-κB signaling cascades which induces the expression of COX-2 and MMP-9 in pRCC cells. Taken together, we conclude that FFA1 and FFA4 signaling have a significant yet complex function in the regulation of cell proliferation, tumor growth, migration, and invasion in pRCC cells.