SUSTAINED NONTUMORIGENIC PHENOTYPE CORRELATES WITH A LARGELY STABLE CHROMOSOME CONTENT DURING LONG-TERM CULTURE OF THE HUMAN KERATINOCYTE LINE HACAT

Altered growth and differentiation and a highly abnormal karyotype are generally believed to be indicators for tumorigenic conversion of hum an cells. Inactivation of TP53 is supposedly one possible mechanism fo r accelerated genetic aberrations via reduced control of the genetic i ntegrity. To examine the significance of this functional relationship, we investigated the long-term development of the spontaneously immort alized human skin keratinocyte line HaCaT, carrying UV-specific mutati ons in both alleles of the TP53 tumor suppressor gene. During >300 pas sages, proliferation, clonogenicity, and serum-independent growth pote ntial increased. In addition, HaCaT cells gained anchorage independenc e and at late passages showed reduced differentiation. Karyotypic anal ysis up to passage 225 revealed a high frequency of translocations and deletions, with a particular increase during passages 30 and 50. Neve rtheless, the HaCaT cells remained nontumorigenic when injected subcut aneously, and noninvasive in surface transplants in nude mice. By comp arative genomic hybridization, we confirmed the karyotypically identif ied phase of increased chromosomal aberrations between passages 30 and 50. However, before and thereafter, the CGH profiles of the individua l chromosomes were largely unchanged, demonstrating that those translo cations-also maintained in later passages-did not cause a gross chromo somal imbalance. Thus, our data suggest that multiple changes often co rrelated with a ''transformed phenotype,'' including extensive karyoty pic alterations and mutational inactivation of TP53, are well compatib le with a nontumorigenic phenotype of the HaCaT cells, and that preser ved chromosomal balance may be crucial for this stability during long- term propagation. (C) 1997 Wiley-Liss, Inc.