Lipids covalently bound to keratins of mouse mammary epithelial cells

Keratin polypeptides obtained from mouse mammary epithelial cells (MMEC) were found to be modified by covalent attachment of lipids. MMEC in primary culture were incubated in 3H-palmitate and treated with 1.5M KCl/1% Triton X-100 to obtain a cytoskeletal (CS) fraction containing primarily keratin and actin filaments. After exhaustive extraction to remove labeled lipids, the CS proteins were separated by gel electrophoresis, and the labeled 46 kD (K18) and 55 kD (K8) keratin polypeptides were excised, subjected to acid hydrolysis and the chloroform-soluble products were resolved on thin layer chromatography. For both keratins, covalently bound lipid included major peaks which co-chromatographed with fatty acid standards. Also, unlabeled lipid resolving with fatty acid standards was found covalently bound to both keratins. The results are discussed in terms of keratin-lipid-membrane interactions.