CA9 and triple-negative breast carcinoma: To conduct these studies, we first coupled biotin ligase (BirA*) to the C-terminus of full length, wild-type (WT) human CA9 (Figure 1a) and expressed the CAIX-BirA* fusion protein constitutively in WT MDA-MB-231 human triple negative breast cancer cells (MDA-MB-231-CAIX-BirA*).