Roles of Major Facilitator Superfamily Transporters in Phosphate Response in $Drosophila$

Abstract

The major facilitator superfamily (MFS) transporter $Pho84$ and the type III transporter $Pho84$ are responsible for metabolic effects of inorganic phosphate in yeast. While the $Pho84$ ortholog Pit1 was also shown to be involved in phosphate-activated MAPK in mammalian cells, it is currently unknown, whether orthologs of $Pho84$ have a role in phosphate-sensing in metazoan species. We show here that the activation of MAPK by phosphate observed in mammals is conserved in $Drosophila$ cells, and used this assay to characterize the roles of putative phosphate transporters. Surprisingly, while we found that RNAi-mediated knockdown of the fly $Pho84$ ortholog dPit had little effect on the activation of MAPK in $Drosophila$ S2R+ cells by phosphate, two $Pho84$/SLC17A1–9 MFS orthologs (MFS10 and MFS13) specifically inhibited this response. Further, using a $Xenopus$ oocyte assay, we show that MSF13 mediates uptake of [33P]-orthophosphate in a sodium-dependent fashion. Consistent with a role in phosphate physiology, MSF13 is expressed highest in the $Drosophila$ crop, midgut, Malpighian tubule, and hindgut. Altogether, our findings provide the first evidence that $Pho84$ orthologs mediate cellular effects of phosphate in metazoan cells. Finally, while phosphate is essential for $Drosophila$ larval development, loss of MFS13 activity is compatible with viability indicating redundancy at the levels of the transporters.Version of Recor