Novel Potential Binding Partners of the C‐terminal Tail of the Sodium Bicarbonate Cotransporter NBCn1

We recently showed that the sodium bicarbonate cotransporter NBCn1 (SLC4A7) is upregulated in human breast carcinomas, in which it is the main pH regulator after acidification. Further, NBCn1 is upregulated after overexpression of the receptor tyrosine kinase ErbB2 in MCF‐7 breast cancer cells. The aim of this work is to identify novel NBCn1 binding partners and address their relevance in breast cancer. We performed GST‐pulldown with the full NBCn1 C‐terminus (NBCn1‐Ct) and GST controls, using lysates from ΔNErbB2‐overexpressing MCF‐7 cells and corresponding vector cells, followed by mass spectrometry. Notably, mitochondrial‐associated proteins were pulled down preferentially in the ΔErbB2+ cells. Other proteins pulled down by NBCn1‐Ct with high specificity included the calcium‐binding proteins S100A13, S100A14 and calmodulin, 14–3‐3 beta, and basigin and Receptor for Activated protein C Kinase 1 (RACK1), both of which are implicated in regulating subcellular localization of other membrane transporters. NBCn1‐Ct also associated directly with several protein kinases and ‐phosphatases including Casein Kinase II, which is predicted to phosphorylate several sites in NBCn1. In conclusion, we identified several potential novel interaction partners of NBCn1‐Ct. Analysis to further validate these findings and address their significance in breast cancer are ongoing.Funding: Danish Cancer Society, Danish Research Council