MARKED REDUCTION OF TYPE-I KERATIN (K14) IN CISPLATIN-RESISTANT HUMANLUNG SQUAMOUS-CARCINOMA CELL-LINES

We have established two cisplatin-resistant human lung squamous-carcin oma cell lines, PC10-B3 and PC10-E5, from their original cell line PC1 0. To discover which proteins are associated with cisplatin resistance , we carried out a two-dimensional gel electrophoresis to analyze diff erences in protein alteration between PC10, PC10-B3 and PC10-E5. A pro tein spot M(r) 50 kDa, pI5.3, was reduced markedly and a spot M(r) 50 kDa, pI4.9 was increased when PC10-B3 and PC10-E5 were compared with P C10. A spot M(r) 58 kDa, pI5.8 newly appeared only in PC10-E5. Cell fr actionation showed that the M(r) 50 kDa, pI5.3 (p50-5.3) and the M(r) 50 kDa, pI4.9 fell within the nuclear fraction, while the M(r) 58 kDa, pI5.8 was found among the cytosol and microsomal fractions. Microsequ encing after in situ digestion of the dramatically reduced spot p50-5. 3 revealed that it was identical to 50 kDa, type I keratin (K14). More over, a retinoic acid-mediated K14 reduction was concomitant with a 4. 0-fold increase in cisplatin resistance in PC10. Our report is the fir st to suggest the possible association of marked K14 reduction and cis platin resistance in PC10-B3 and PC10-E5.