INDUCTION OF SENESCENCE-LIKE PHENOTYPES BY FORCED EXPRESSION OF HIC-5, WHICH ENCODES A NOVEL LIM MOTIF PROTEIN, IN IMMORTALIZED HUMAN FIBROBLASTS

The hic-5 gene encodes a novel protein with Zn finger-like (LIM) motif s, the expression of which increases during cellular senescence. The e ctopic expression of hic-5 in nontumorigenic immortalized human fibrob lasts, whose expression levels of hic-5 were significantly reduced in comparison with those of mortal cells, decreased colony-forming effici ency. Stable clones expressing high levels of hic-5 mRNA showed higher levels of mRNAs for several extracellular matrix-related proteins, al ong with the alteration of an alternative splicing as seen in senescen t cells and decreased c-fos inducibility. Furthermore, these clones ac quired a senescence-like phenotype, such as growth retardation; senesc ence-like morphology; and increased expression of Cip1/WAF/sdi1 after 20 to 40 population doublings. On the other hand, antisense RNA expres sion of hic-5 in human normal diploid fibroblasts delayed the senescen ce process. HIC-5 was localized in nuclei and had affinity for DNA. Ba sed on these observations, we speculated that HIC-5 affected the expre ssion of senescence-related genes through interacting with DNA and the reby induced the senescence-like phenotypes. To our knowledge, hic-5 i s the first single gene that could induce senescence-like phenotypes i n a certain type of immortalized human cell and mediate the normal pro cess of senescence.