Casein kinase II is associated with neurofibrillary tangles but is not an intrinsic component of paired helical filaments.

Neurofibrillary tangles (NFT) are pathological cytoskeletal structures composed of paired helical filaments (PHF), and are found in neurons of patients afflicted with many neurodegenerative disorders, including Alzheimer's disease (AD). We previously found that an antiserum against casein kinase II (CK-II) stained NFT intensely in the brain tissue of AD patients. In the current study, we found that the anti-CK-II antiserum stains NFT and neuronal inclusions in many other neurodegenerative diseases as well, including Guam-Parkinson dementia complex, chromosome 18 deletion syndrome, progressive supranuclear palsy, Kufs' disease, and Pick's disease. This antiserum reacted, in crude brain homogenates, with both a doublet of Mr 43,000 and a Mr 27,000 Da protein which could correspond to the alpha, alpha', and beta chains of CK-II. The staining of these bands was adsorbed by preincubating anti-CK-II antiserum with purified CK-II. Preincubation of brain sections with purified CK-II strongly intensified the immunostaining of NFT with anti-CK-II, suggesting that NFT may bind CK-II. In the AD brain homogenates, the particulate CK-II levels are increased whereas the cytosolic levels are decreased without a change in total CK-II levels, consistent with the idea that CK-II binds to the particulate PHF, a major constituent of NFT. In accord with these findings, purified PHF bound CK-II, but purified PHF did not contain CK-II as its component. These results suggest that CK-II might be an extraneously deposited component of NFT. Thus, the altered CK-II compartmentalization might have significant consequences in the pathogenesis of AD.