p19^Arf induces p53-dependent apoptosis during Abelson virus-mediated pre-B cell transformation

The Ink4a/Arf locus encodes p16^Ink4a and p19^Arf and is among the most frequently mutated tumor suppressor loci in human cancer. In mice, many of these effects appear to be mediated by interactions between p19^Arf and the p53 tumor-suppressor protein. Because Tp53 mutations are a common feature of the multistep pre-B cell transformation process mediated by Abelson murine leukemia virus (Ab-MLV), we examined the possibility that proteins encoded by the Ink4a/Arf locus also play a role in Abelson virus transformation. Analyses of primary transformants revealed that both p16^Ink4a and p19^Arf are expressed in many of the cells as they emerge from the apoptotic crisis that characterizes the transformation process. Analyses of primary transformants from Ink4a/Arf null mice revealed that these cells bypassed crisis. Because expression of p19^Arf but not p16^Ink4a induced apoptosis in Ab-MLV-transformed pre-B cells, p19^Arf appears to be responsible for these events. Consistent with the link between p19^Arf and p53, Ink4a/Arf expression correlates with or precedes the emergence of cells expressing mutant p53. These data demonstrate that p19^Arf is an important part of the cellular defense mounted against transforming signals from the AbI oncoprotein and provide direct evidence that the p19^Arf-p53 regulatory loop plays an important role in lymphoma induction.