Zacchia and colleagues found that media acidification activates the citrate transporter NaDC-1 through Raf1, ERK1/2 and p90RSK signalling in the opossum kidney proximal tubule cells, suggesting that ERK1/2 and p90RSK may play a role in hypocitraturia and kidney stone formation [48]. Here, MAPK3 is linked to nephrolithiasis.