ADP-ribosylation results from transfer of the
ADP-ribose moiety of
nicotinamide adenine dinucleotide (
NAD) to an acceptor with
ADP-ribose-acceptor content determined by the activities of
ADP-ribosyltransferases, which modify the acceptor, and
ADP-ribose-acceptor
hydrolase (ARH), which cleave the
ADP-ribose-acceptor bond. ARH1 was discovered as an
ADP-ribose(
arginine)
protein hydrolase. Previously, we showed that ARH1-knockout and ARH1 heterozygous mice spontaneously developed
tumors. Further, ARH1-knockout and ARH1 heterozygous mouse embryonic fibroblasts (MEFs) produced
tumors when injected into nude mice. In
tumors arising in ARH1 heterozygous mice and MEFs, we found both loss of heterozygosity (LOH) of the ARH1 gene and ARH1 gene mutations. In the present report, we found that these mutant ARH1 genes encode
proteins with reduced ARH1 enzymatic activity. Moreover, MEFs transformed with ARH1 mutant genes exhibiting different levels of ARH1 activity showed altered rates of proliferation, anchorage-independent colony growth in soft
agar, and
tumorigenesis in nude mice. MEFs transformed with the wild-type (WT) gene, but expressing low levels of
hydrolase activity were also tumorigenic. However, transformation with the WT gene was less likely to yield
tumors than transformation with a mutant gene exhibiting similar
hydrolase activity. Thus, control of
protein-ADP-ribosylation by ARH1 is critical for
tumorigenesis. In the human
cancer database, LOH and mutations of the ARH1 gene were observed. Further, ARH1 gene mutations were located in exons 3 and 4, comparable to exons 2 and 3 of the murine ARH1 gene, which comprise the catalytic site. Thus, human ARH1 gene mutations similar to their murine counterparts may be involved in human
cancers.