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) motifs, the expression of which increases during cellular senescence. The ectopic expression of hic-5 in nontumorigenic immortalized human fibroblasts, whose expression levels of hic-5 were significantly reduced in comparison with those of mortal cells, decreased colony-forming efficiency. Stable clones expressing high levels of hic-5 mRNA showed higher levels of mRNAs for several extracellular matrix-related proteins, along with the alteration of an alternative splicing as seen in senescent cells and decreased c-fos inducibility. Furthermore, these clones acquired a senescence-like phenotype, such as growth retardation; senescence-like morphology; and increased expression of Cip1/WAF1/sdi1 after 20 to 40 population doublings. On the other hand, antisense RNA expression of hic-5 in human normal diploid fibroblasts delayed the senescence process. HIC-5 was localized in nuclei and had affinity for DNA. Based on these observations, we speculated that HIC-5 affected the expression of senescence-related genes through interacting with DNA and thereby induced the senescence-like phenotypes. To our knowledge, hic-5 is the first single gene that could induce senescence-like phenotypes in a certain type of immortalized human cell and mediate the normal process of senescence.