KERATIN BIOSYNTHESIS IN NORMAL MOUSE EPITHELIA AND IN SQUAMOUS-CELL CARCINOMAS - MESSENGER RNA-DEPENDENT ALTERATIONS OF THE PRIMARY STRUCTURE OF DISTINCT KERATIN SUBUNITS IN TUMORS

  • 1 January 1983
    • journal article
    • research article
    • Vol. 258  (21) , 3268-3272
Abstract
The keratin polypeptide patterns of 2 murine transplantable squamous cell carcinomas-originally induced by chemical means in the back skin and in the forestomach epithelium-are deficient in high MW keratin subunits (> 60 kDa [kilodaltons]) invariably present in the corresponding normal tissues. In addition, the keratin polypeptide composition within the low MW range showed further alterations with regard to the corresponding keratin subset of normal tissues in that both tumors expressed a 40 kDa protein, and a 56 kDa protein was selectively found in the forestomach tumor. A comparison of the charge properties of normal and tumor keratin polypeptides revealed that the 2 uppermost tumor proteins at 60 and 58 kDa were basic in nature whereas their normal MW counterparts belonged to the acidic subset of the pattern. These tumor proteins also showed mutually identical peptide maps which, however, were considerably different from those of the normal proteins. The remaining tumor keratin subunits at 52, 50, 48, and 45 kDa, common also to the normal tissues, had retained their normal charge properties. In vitro translation of mRNA, isolated from both normal and tumor tissue, revealed that every tumor keratin polypeptide is encoded by its own mRNA. In contrast to normal keratinizing tissues, there is therefore no indication of post-translational protein processing in tumors. The in vitro translation products of tumor RNA had all properties in common with the in vivo proteins, thus indicating that every deviation of the tumor keratin spectrum from the normal state is determined at the mRNA level.