Marked reduction of type I keratin (K14) in cisplatin-resistant human lung squamous-carcinoma cell lines

We have established two cisplatin-resistant human lung squamous-carcinoma cell lines, PC10-B3 and PC10-E5, from their original cell line PC10. To discover which proteins are associated with cisplatin resistance, we carried out a two-dimensional gel electrophoresis to analyze differences in protein alteration between PC10, PC10-B3 and PC10-E5. A protein spot M r 50 kDa, p15.3, was reduced markedly and a spot M r 50 kDa, p14.9 was increased when PC10-B3 and PC10-E5 were compared with PC10. A spot M r 58 kDa, pI5.8 newly appeared only in PC10-E5. Cell fractionation 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. Microsequencing after in situ digestion of the dramatically reduced spot p50–5.3 revealed that it was identical to 50 kDa, type I keratin (K14). Moreover, a retinoic acid-mediated K14 reduction was concomitant with a 4.0-fold increase in cisplatin resistance in PC10. Our report is the first to suggest the possible association of marked K14 reduction and cisplatin resistance in PC10-B3 and PC10-E5.