Phosphate uptake-independent signaling functions of the type III sodium-dependent phosphate transporter, PiT-1, in vascular smooth muscle cells

• Published in: Experimental cell research Vol. 333; no. 1; pp. 39 - 48
• Main Authors: Chavkin, Nicholas W., Chia, Jia Jun, Crouthamel, Matthew H., Giachelli, Cecilia M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 10-04-2015; Elsevier BV
• Subjects: Animals; Biological Transport; Calcification; Cell Differentiation; Cells, Cultured; Cellular biology; ERK phosphorylation; Extracellular Signal-Regulated MAP Kinases - metabolism; Kidney diseases; Mice, Inbred C57BL; Mice, Transgenic; Muscle, Smooth, Vascular - pathology; Myocytes, Smooth Muscle - metabolism; Phosphate; Phosphates - metabolism; PiT-1; Protein Processing, Post-Translational; Signal Transduction; Signaling; SLC20A1; Sodium; Sodium-Phosphate Cotransporter Proteins, Type III - physiology; Vascular Calcification - metabolism; Calcification; Signaling; SLC20A1; ERK phosphorylation; Phosphate; PiT-1
• ISSN: 0014-4827; 1090-2422
• DOI: 10.1016/j.yexcr.2015.02.002

Vascular calcification (VC) is prevalent in chronic kidney disease and elevated serum inorganic phosphate (Pi) is a recognized risk factor. The type III sodium-dependent phosphate transporter, PiT-1, is required for elevated Pi-induced osteochondrogenic differentiation and matrix mineralization in vascular smooth muscle cells (VSMCs). However, the molecular mechanism(s) by which PiT-1 promotes these processes is unclear. In the present study, we confirmed that the Pi concentration required to induce osteochondrogenic differentiation and matrix mineralization of mouse VSMCs was well above that required for maximal Pi uptake, suggesting a signaling function of PiT-1 that was independent of Pi transport. Elevated Pi-induced signaling via ERK1/2 phosphorylation was abrogated in PiT-1 deficient VSMCs, but could be rescued by wild-type (WT) and a Pi transport-deficient PiT-1 mutant. Furthermore, both WT and transport-deficient PiT-1 mutants promoted osteochondrogenic differentiation as measured by decreased SM22α and increased osteopontin mRNA expression. Finally, compared to vector alone, expression of transport-deficient PiT-1 mutants promoted VSMC matrix mineralization, but not to the extent observed with PiT-1 WT. These data suggest that both Pi uptake-dependent and -independent functions of PiT-1 are important for VSMC processes mediating vascular calcification.
•PiT-1 is required for ERK1/2 phosphorylation in response to elevated phosphate.•Phosphate uptake through PiT-1 is not required for ERK1/2 phosphorylation.•Transport-independent PiT-1 function promotes osteochondrogenic phenotype change.•Transport-dependent and -independent PiT-1 functions are required for mineralization.