Further experiments have shown that p8 mRNA is activated in almost all cells in response to several stresses, including minimal stresses sellckchem such as after rou tine change of the culture medium in the absence of any added substance, indicating that p8 is a ubiquitous protein induced by cellular stress. The p8 gene was cloned in human, rat, mouse, and Xenopus laevis, concep tually translated from the Drosophila Inhibitors,Modulators,Libraries melanogaster genome or deduced from EST libraries. The overall degree of homology with human p8 ranged from 81 to 40%. Secondary structure prediction methods indicated that within the homologous region of the eleven proteins, there is a basic Helix Loop Helix sec ondary structure motif, characteristic of some classes of transcription factors.

Even though a small protein such as p8 would not need a nuclear localization signal to be transported to Inhibitors,Modulators,Libraries the nucleus, a clear NLS can be pre dicted for the eleven proteins comprising a bipartite domain of positively charged aminoacids. In addition, a nuclear/cytoplasmic location has been demonstrated for human p8 upon overexpression of the recombinant pro tein and immunohistochemistry, and for recombinant Xenopus laevis p8 fused to green fluorescent protein. Homology searching in databases did not reveal signifi cant Inhibitors,Modulators,Libraries similarity of p8 with other proteins of known func tion. However, biochemical properties of the mammalian p8 proteins are shared by some high mobility group pro teins, particularly by the HMG I/Y family.

The overall identity of human p8 with human HMG I/Y is only about 35%, but the molecular mass, isoelectric Inhibitors,Modulators,Libraries point, hydrophilicity plot, the resistance to denaturation after heating at 100 C and the charge separation are very similar. The Inhibitors,Modulators,Libraries p8 protein seems to bind DNA weakly, as shown by electrophoretic mobility shift assay, without preference for DNA sequences. Finally, human p8 has also been shown to be a substrate for protein kinase A in vitro and phosphorylated p8 has a higher content of secondary structure and binding to DNA is highly increased. An architectural role in transcription has been proposed for this protein, in analogy with the HMG I/Y proteins, and a recent work seems to confirm this hypothesis. Functions of p8 appear to be multiple and complex. For example, p8 mRNA expression was strongly induced in 3T3 cells upon TGF 1 treatment which in turn enhances the Smad transactivating function responsible for TGF 1 activity. We also found that p8 is involved in cell cycle regulation since p8 deficient embryonic fibroblasts grew more rapidly and incorporated meantime more thymidine and BrdU than p8 expressing cells. Moreover, expres sion of p8 in breast cancer derived cells seems to mediate the inhibition of cell growth induced by 1,25 Dihydroxy vitamin D3.