Evidence of differentiated keratin peptide (K1) in cultured human squamous cell carcinomas: demonstration of generality by three different approaches.

The largest keratin peptide (K1, 68KD) has not been detectable in cultured human squamous cell carcinomas. However, quite recently, the K1 peptide was clarified to be present in two kinds of cultured HSC by using a low salt aqueous solution, rather than the high salt and Triton X-100 employed by many previous researchers (Biochem. Biophys. Res. Commun., 182, 1440-1445, 1992). To determine whether this phenomenon is common or not in cultured HSCs, I further demonstrated the K1 peptide by extracting it with two different buffers and by 2D-PAGE, immunological techniques, and Northern blot analysis, using another kind of HSC. Until now, keratin extraction has been done using high salt/Triton X-100 solution, during which K1 peptide may be removed because it has developed an affinity with the buffer. Many investigators may have therefore overlooked it.