KLF15: Proteins and Enzymes

The kidney chloride channel proteins CLCNKA and CLCNKB are highly related, although they are located in different areas of the kidney. Using a yeast 1-hybrid screen of a kidney cDNA library with the GA element of the CLCNKA promoter as bait, Uchida et al. (2000) isolated cDNAs encoding MAZ and KLF15, which they termed KKLF. Sequence analysis predicted that the 415-amino acid KLF15 protein, which is 84% identical to the rat Klf15 protein, contains 3 zinc finger motifs at its C terminus, N-terminal serine-rich stretches, and a central proline-rich segment. EMSA analysis confirmed that KLF15 and MAZ interact with the GA element of the CLCNKA promoter and showed that KLF15 binds with higher affinity and is a functional competitor of MAZ. Northern blot analysis revealed highest expression of a 2.5-kb KLF15 transcript in liver, followed by heart, skeletal muscle, and kidney. No expression was found in bone marrow or lymphoid tissues. Western blot analysis showed expression of a 50-kD protein. Immunohistochemical analysis detected nuclear expression of KLF15 in liver sinusoid stellate cells, subcapsular fibroblasts, and portal fibroblasts. KLF15 was also expressed in cardiac and skeletal muscle interstitial cells and in kidney inner medulla, glomeruli, and cortical interstitium. Immunofluorescence microscopy, however, demonstrated no colocalization of KLF15 with CLCNKA.