Molecular determinants for apical expression and regulatory membrane retrieval of the type IIa Na/Pi cotransporter

Renal inorganic phosphate (Pi) reabsorption is a key process in Pi homeosta sis. Type IIa Na/Pi cotransporters, Located at the api cal membrane of rena l proximal tubular cells, guarantee the vectorial transport of Pi. Renal Pi reabsorption can be modulated by controlling the number of cotransporters expressed at the apical membrane. Indeed, factors that increase Pi reabsorp tion induce the expression of type Iia cotransporters at the apical membran e, whereas factors that decrease Pi reabsorption lead to their retrieval. T herefore, proper sorting of this type of cotransporters is an essential ste p in Pi homeostasis. The relevance of polarization has been highlighted by the finding that improper sorting of transporters can cause disease. Here w e describe the identification of signals involved in apical expression of n ewly synthesized type IIa cotransporters and in their hormonal-induced endo cytosis.